Journal of the Society of Amateur Radio Astronomers January- February 2015
RADIO
ASTRONOMY Journal of the Society of Amateur Radio Astronomers
January- February 2015
1 Radio Waves President’s Page 3 Editor’s Note 4
News Ken Redcap SARA President 2015 SARA Western Regional Conference Western Conference Abstracts 6 Kathryn Hagen Mark Your Calendar 10 Editor Call for Nomination 11 Whitham D. Reeve SARA Annual Conference at NRAO 11 Contributing Editor Call for Papers: 2015 SARA Annual Conference 12
Christian Monstein New Website Sections Introduced; Further Enhancements to Come 12 Contributing Editor
Stan Nelson Feature Articles Contributing Editor Slooh Broadcasts with Radio Meteor Audio‐ Stan Nelson 14 The Big Bang is Bunk‐ Grote Rebe r 16 Lee Scheppmann Technical Editor PstRotator Antenna Rotator Software Application for Radio Astronomy ‐ Whit Reeve 23 Radio Astronomy is published bimonthly as the Cassiopeia: A Scintillation Observed by Radio JOVE Participants ‐Dave official journal of the Society of Amateur Radio Astronomers. Duplication of uncopyrighted Typinski et al 31 material for educational purposes is permitted Leap Second to be Added in 2015!‐‐Whit Reeve 37 but credit shall be given to SARA and to the specific author. Copyrighted materials may not RASDRviewer Pulsar Feature Description ‐ Paul L. Oxley 39 be copied without written permission from the Radio‐Frequency Interference (RFI) From Extra‐High‐Voltage (EHV) copyright owner. Transmission Lines‐Patrick C. Crane 45
Radio Astronomy is available for download only Callisto‐Pi: Callisto Spectrograms from Rasperry Pi‐‐Whit Reeve 79 by SARA members from the SARA web site and First Light of TLM‐18 Antenna 85 may not be posted anywhere else. Book Review—Radio Propagation 86
It is the mission of the Society of Amateur Radio Astronomers (SARA) to: Facilitate the flow of Membership information pertinent to the field of Radio As‐ tronomy among our members; Promote New Members 88 members to mentor newcomers to our hobby Membership Dues and Promotions 88 and share the excitement of radio astronomy with other interested persons and organizations; Promote individual and multi station observing Administrative programs; Encourage programs that enhance the Officers, directors and additional SARA contacts 90 technical abilities of our members to monitor cosmic radio signals, as well as to share and analyze such signals; Encourage educational Resources programs within SARA and educational outreach Great Projects to Get Started in Radio Astronomy 91 initiatives. Founded in 1981, the Society of Amateur Radio Astronomers, Inc. is a Education Links 93 membership supported, non‐profit [501(c) (3)], Online Resources 95 educational and scientific corporation.
Copyright © 2015 by the Society of Amateur For Sale, Trade, Wanted Radio Astronomers, Inc. All rights reserved. SARA Polo Shirts 96
For Sale 96 Photograph: Control room, 40‐Meter Telescope, Owens Valley Radio Observatory
2 ‐Radio Waves
President’s Page
SARA had a booth at the 2015 HAMcation event in Orlando, FL. Many thanks go out to Melinda and Tom and Lynn Crowley for their help in supporting this effort. We got to meet a number of RA enthusiasts and talked a great deal on Software Defined Radio (SDR), SuperSID and Radio Jove just to name a few topics. Just as HAMvention doubled in size for SARA this year HAMcation could do the same in May.
There is still time to register for the 2015 Western Conference to be held at Standford University in Palo Alto, California March 20 to 22. More information is in this Journal as well as on‐line at http://www.radio‐ astronomy.org/meetings.
It may seem a long way off, but we need to be thinking about officers and directors nominations. If you are interested in serving as secretary, treasurer, director or director‐at‐large, let me know. Also, take a minute to look at the responsibilities and duties of these positions at http://www.radio‐astronomy.org/pdf/operating‐procedures.pdf.
The Annual Eastern Conference is set for June 21 to June 24, 2015 at the National Radio Astronomy Observatory in Green Bank, West Virginia. More details are available on‐line at http://www.radio‐astronomy.org/meetings and in upcoming Journals.
May your noise figure be low, Ken Redcap KR5ARA
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Editor’s Notes
We are always looking for basic radio astronomy articles, radio astronomy tutorials, theoretical articles, application and construction articles, news pertinent to radio astronomy, profiles and interviews with amateur and professional radio astronomers, book reviews, puzzles (including word challenges, riddles, and crossword puzzles), anecdotes, expository on “bad astronomy,” articles on radio astronomy observations, suggestions for reprint of articles from past journals, book reviews and other publications, and announcements of radio astronomy star parties, meetings, and outreach activities.
If you would like to write an article for Radio Astronomy, please follow the Author’s Guide on the SARA web site: http://www.radio‐astronomy.org/publicat/RA‐JSARA_Author’s_ Guide.pdf. You can also open a template to write your article http://www.radio‐astronomy.org/publicat/RA‐JSARA_Article_Template.doc
Let us know if you have questions; we are glad to assist authors with their articles and papers and will not hesitate to work with you. You may contact your editors any time via email here: editor@radio‐astronomy.org.
I will acknowledge that I have received your submission within two days. If I don’t, assume I didn’t receive it and please try again.
Please consider submitting your radio astronomy observations for publication: any object, any wavelength.
Strip charts, spectrograms, magnetograms, meteor scatter records, space radar records, photographs;
examples of radio frequency interference (RFI) are also welcome.
Guidelines for submitting observations may be found here: http://www.radio‐astronomy.org/publicat/RA‐
JSARA_Observation_Submission_Guide.pdf
Tentative Radio Astronomy due dates and distribution schedule
Issue Articles Radio Waves Review Distribution
Jan – Feb February 12 February 20 February 23 February 28
Mar – Apr April 12 April 20 April 25 April 30 May – Jun June 12 June 20 June 25 June 30 Jul – Aug August 12 August 20 August 25 August 31
Sep – Oct October 12 October 20 October 25 October 31 Nov – Dec December 12 December 15 December 20 December 31
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News
2015 SARA Western Regional Conference
Palo Alto, California, USA on 20 ‐ 22 March 2015
The 2015 SARA Western Regional Conference will be held at Stanford University in Palo Alto, California on Friday, Saturday and Sunday, 20 ‐ 22 March 2015. The meeting will include a visit the Kavli Institute for Particle Astrophysics and Cosmology (KIPAC).
Presentations and proceedings: In addition to presentations by SARA members, we plan to have speakers from the Stanford University faculty, SETI Institute, Allen Telescope Array and possibly KIPAC. Papers and presentations on radio astronomy hardware, software, education, research strategies, philosophy, and observing efforts and methods are welcome. Formal proceedings will be published for this conference. If presenters want to submit a paper or a copy of their presentation, we will make them available to attendees on CD.
Basic schedule: Our first day will include a visit to the KIPAC facilities at Stanford Linear Accelerator Center (SLAC). The next two days' meetings will take place on the Stanford University campus and will include presentations by members and guest speakers.
Getting there: Fly into San Jose or San Francisco airports and rent a car to drive to Palo Alto.
Registration: Registration for the 2015 Western Regional Conference is just US$55.00. This includes breakfast and lunch on Saturday and Sunday. Payment can be made through PayPal, www.paypal.com by sending payment to treasurer@radio‐astronomy.org. Please include in comments that the payment is for the 2015 Western Regional Conference. You also can mail a check payable to SARA, 2189 Redwood Ave, Washington, IA 52353, USA. Please include an e‐mail address so a confirmation can be sent to you when we receive your payment.
Hotel reservations: Marriott Courtyard Palo Alto Los Altos Marriott hotel(s) offering SARA a special group rate: Courtyard Palo Alto Los Altos for 129.00 USD per night, Last day to book by: 3/5/15 http://www.marriott.com/meeting-event-hotels/group-corporate- travel/groupCorp.mi?resLinkData=SARA^paocy%60sarsara|sarsarb%60129.00%60USD%60false%603 /19/15%603/23/15%603/5/15&app=resvlink&stop_mobi=yes
What to wear: Our conference settings are casual.
Saturday night dinner: We will make a group dinner reservation at a local restaurant for Saturday night.
Additional Information: Additional details will be published online at www.radio‐astronomy.org/meetings and in the SARA journal, Radio Astronomy, as we get closer to the conference date. Please contact conference coordinators David Westman and Keith Payea if you have any questions or if you would like to help with the conference: westernconference@radio‐astronomy.org.
5 Western Conference 2015 Abstract
Author: Tom Hagen Title: Portable VLF Receiver for Making Calibrated Magnetic Field Strength Measurements
Abstract: This presentation is about the author's continuing efforts to get calibrated measurements of the field strengths of the various VLF stations used by the SuperSID program as reference sources to detect sudden ionospheric disturbances (SID’s). Presently, the amplitude of data coming in from the various SuperSID stations around the world is uncalibrated. When a SID is detected, there is a measurable change in relative signal strength, but actual field strengths are unknown. If a portable VLF receiver and loop antenna setup could be developed that is calibrated, then such a setup could be shipped to different sites for calibrated field strength measurements. Users could even build their own receiver and loop antenna from standard plans. A small loop design and two receiver designs are discussed. Estimated sensitivities of each receiver design are calculated. Calculations are verified with laboratory tests.
Author: Curt Kinghorn
Abstract: One of the following: 1. Converting drift scan lines from one of my radio telescopes to a full‐fledged sky map/image. This is proving more challenging than I initially thought but the final product is also proving to be more rewarding in that the results looks more like what the sky would look like if I were looking at in through "radio‐eyes." 2. Inserting a time delay in one leg of an interferometer to get "steering" without having to move the antenna (sort of analogous to phased‐array radar)! 3. Comparing the results of my 611 MHz radio telescope using an ICOM R7000 receiver with that same system only with a FunCube Dongle Software Defined Radio receiver. (So far, the ICOM is the undisputed champion but I am hoping to improve the performance of the SDR system!) 4. Converting a commercial satellite antenna positioner (used by commercial TV station remote units to send their remote signals to the "home" station) to (much more precisely!) aim the antenna for either my 611 MHz or my 12.2 ‐ 12.7 GHz radio telescope antennas.
Author: Whitham D. Reeve, Anchorage, Alaska USA, SARA Member Title: Sudden Frequency Deviations Due to Solar Flares
Abstract: This paper describes the interesting phenomena of Sudden Frequency Deviations (SFD), which are changes in the received frequency of a fixed carrier caused by rapid changes in Earth’s ionosphere from a solar flare. For purposes of this study I recorded WWV and WWVH time service signals received at Anchorage, Alaska USA between early June and end of December 2014. Part I describes the concepts of sudden frequency deviations in terms of solar flares and ionospheric propagation, and Part II describes the instrumentation and observations during the study period.
WWV and WWVH transmit continuous radio frequency carriers with very high accuracy and stability on 2.5, 5, 10 and 15 MHz. WWV also transmits on 20 MHz and in April 2014 restarted transmitting on 25 MHz. The transmitted carrier frequencies are accurate to a few parts in 1013 (about 0.000 000 000 000 3 Hz), but the short‐ term accuracy is degraded to a few parts in 109 during normal propagation to distant receivers. Sudden frequency deviations lasting a minute or more due to solar flares can be two or three orders of magnitude worse.
Two ionospheric conditions are attributed to sudden frequency deviations, both caused by the x‐ray and extreme ultra‐violet (EUV) energy released by a solar flare and reaching Earth a little more than 8 minutes later. First, a slab of ionosphere below the reflection region undergoes a rapid change in refraction index and, second,
6 the ionosphere’s reflection region undergoes a rapid vertical movement. Both conditions change the propagation path length and introduce a Doppler shift in the radio wave. Either one or both can cause a sudden frequency deviation. It is interesting to note that sudden frequency deviations are correlated with solar flares but due to the variability in the spectral content of flares at x‐ray and EUV wavelengths, only a fraction of all flares cause an SFD.
The method of detecting sudden frequency deviations described here is quite sensitive (the weakest x‐ray flare detected in the study period was C1.8) and the technique may be helpful in verifying sudden ionospheric disturbances (SID) at very low frequencies. SFDs were studied extensively in the 1960s but there appears to have been little work since then.
Author: Dean Knight Title: A Student’s Hands‐on Introduction to Radio and Radio‐astronomy
Abstract: The engaging introduction to radio electronics for students can involve the construction, modification and testing of a tunable (VHF/UHF) solar radio telescope of a tweeked Jove dual‐dipole design, incorporating a simple 1 transistor circuit, common household materials and Radio‐SkyPipe. Students are able to easily experiment (and establish controls) with the parameters of a radio telescope, thus allowing them to explore the effects of these modifications on both the observed frequency and amplitude of the processed incoming radio signal.
Author: Ken Redcap (KR5ARA) Title: 611 MHz Total Power Radio Telescope ‐ Part 0x03 (Software)
Abstract: Part 0x02 of this presentation was given at the SARA 2014 East Conference. Parts 0x01 and 0x02 dealt with the hardware (antennas (< $100 each), USB dongle (< $30), etc.) being used for this ongoing project. Part 0x03 will focus on the programs available on the website SDRSharp.Com and how to make modifications. Other topics will include Visual Studio (Microsoft) used to build the application SDRSharp and an introduction to the new hardware (AIRSPY ($200)) available on the same website that is compatible with SDRSharp. This project is a work in progress and is my first effort on a radio telescope to detect energy in this frequency range. The telescope is being set up at the McMath Hulbert Solar Observatory (MHO) in Lake Angelus, MI. All electronic components and antennas required were purchased from Amazon except for the low noise amplifier. All freeware software components were derived from sites with various versions of SDR# like SDRSharp.Com. Inspiration for the project comes from Kurt Kinghorn's presentation at the 2013 SARA Western Conference on low cost radio telescopes using off‐the‐shelf TV receive antennas and an article in the August, 2013 SARA Journal about a low cost HI receiver.
Author: Ray Fobes (W1OTH) Title: The Dipole Array Radio telescope (DART)
Abstract: The radio astronomy observatory at Embry‐Riddle Aeronautical University, Prescott is in the process of designing and installing a cross‐dipole phased array radio telescope. The principal purposes of this telescope are to provide students with a research grade radio telescope for enhancing their space physics and astronomy curriculum as well as performing long term pulsar timing in support of programs like LIGO.
Based on the low frequency demonstrator of the original Mileura Widefield Array (now at the Murchison Widefield Array) we will be building a three tile, 110 – 300 MHz phased array telescope with direct sampled rf and signal processing in the digital domain. 30 MHz of bandwith can be directly sampled from each of the tiles simultaneously. Each tile will have up to 10 m2 collecting area with maximum gain in the 200‐250 MHz region, ideal for pulsar monitoring. Rapid all sky pointing above 30 deg in both polarizations will be available.
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In addition to characterizing the radio sky and tracking pulsar timing the telescope will also be available for long term solar research including the heliopause as well as passive and active ionospheric studies.
This presentation will describe the design and construction of the DART telescope.
Author: Tushar Sharma, Dhruv Bhaskar ,Ramzi Darraji, Fadhel Ghannouchi Electrical and Computer Engineering Department, University of Calgary, Canada Title: Radio Jove Instrumentation and Education Outreach
Abstract: This paper looks into the effect of varying parameters on different antenna designs with an aim to achieve an optimized antenna design that can be used with the Radio Jove kit. As a team of amateur radio astronomers, we have simulated the response of different antennae on Numerical Electromagnetic Code – 2 which uses the method of moments solution of the electric field integral equation and the magnetic field integral equation for closed, conducting surfaces. By varying the geometries (height above ground, diameter of loops, lengths of dipoles, tuning capacitors etc.) of antenna structures, we have observed how different parameters affect gain, directivity, V.S.W.R. and thus the cumulative efficiency of antennae. It is quite apparent that many minute factors play a key role in determining antenna performance. All the antenna designs have been optimized for a frequency of 20.1 MHz, which is the operating frequency of the Radio Jove setup. The Radio JOVE kit makes use of a dipole antenna which is relatively huge in size (because of the operating frequency of 20.1 MHz). Another aim of our research is to reduce the overall antenna size while maintaining performance. Simulation results have proved that a loop antenna poses as a potential substitute, as it can be constructed fairly easily and for a low cost.
While experimental results are under way, we present the data collected from simulations in this paper. This data will provide an insight into the different factors affecting antenna response and can potentially lead to an optimized, easy – to – use Radio JOVE kit. With setting up of Astronomical Teacher training Institute in Alberta, Canada we have introduced different programs including STAR , Summer Grant with IEEE MTT chapter, Winter Grant and Student‐Mentor .With collaboration with IEEE to support student activities in field of Radio Science and engineering future goals are setting up of amateur observatories in school across Alberta.
Author: Jack Welch, UC Berkeley Graduate School Title: Low Noise Feeds for the Allen Telescope Array
Abstract: The goals for the Allen Telescope Array (ATA) antennas are low background noise and wide bandwidth. To achieve the low background pick‐up from the ground, the antenna optics uses an offset Gregorian secondary. To achieve the wide bandwidth, a log‐periodic antenna is used for the feed. The log‐periodic feed is tapered with its shortest operating wavelength give by the dimension of its small end, and its longest wavelength given by size of the large end. For the ATA. The range is 0.9 GHz to 15 GHz; four octaves. At any particular frequency in that range, the active portion of the feed is relatively small. One awkward feature for the log‐periodic is that all wavelengths are received from the direction of the small end, and the input terminals for the low noise amplifier must be at the small end. The receiver box must be fitted within the large end of the log‐periodic structure with coaxial cables extended to the tip. To avoid losses in these cables and in the feed, the entire structure is cooled to 70K. The input amplifier produces very little noise at that temperature. Achieving the low physical temperature requires that the feed and receiver be enclosed in a transparent bottle. The low background of the Gregorian optics and the cooled amplifier and feed combine to deliver very low system temperatures for the array. The forty‐two antennas of the ATA are currently being outfitted with these new receiver systems, thanks to a generous donation from Franklin Antonio.
Author: Jon Richards, SETI Institute
8 Title: The Signal Search at the Allen Telescope Array
Abstract: This presentation will provide an overview the Allen Telescope Array (ATA), located in Northern California. The ATA is the instrument the SETI Institute's Center for SETI Research uses to search for extraterrestrial radio signals. The ATA has 42 radio dishes, each 20 feet in diameter able to detect signals between 1GHz and 10GHz. Jon will cover how the SETI signal search program works, what hardware is used, how the signals are detected, as well as review the current state of the effort. There will also be a discussion of the beginning efforts to use commercial software defined radio devices to aid in several aspects of operations.
Author: Leif Svalgaard Title: "Radio, Ionosphere, Magnetism, and Sunspots"
Abstract: When Marconi in 1902 demonstrated radio communication across the Atlantic Ocean at a distance of 2000 miles it became clear that an electric 'mirror' existed high in the atmosphere to guide the radio waves around the curvature of the Earth. Kennelly and Heaviside independently suggested that a layer of ionized gas, the 'ionosphere' at an altitude of 60‐100 miles was responsible for the effect, but it was only more than two decades later that the existence of such a layer was firmly established by the British scientist Appelton for which he received the 1947 Nobel Prize in Physics. Physicists long resisted the idea of the reflecting layer because it would require total internal reflection, which in turn would require that the speed of light in the ionosphere would be greater than in the atmosphere below it. It was an example of where the more physics you knew, the surer you were that it couldn't happen. However, there are two velocities of light to consider: the phase velocity and the group velocity. The phase velocity for radio waves in the ionosphere is indeed greater than the Special Relativity speed limit making total internal reflection possible, enabling the ionosphere to reflect radio waves. Within a conducting layer electric currents can flow. The existence of such currents was postulated as early as 1882 by Balfour Stewart to explain a the diurnal variation [discovered in 1722] of the Earth's magnetic field as due to the magnetic effect of electric currents flowing in the high atmosphere, such currents arising from electromotive forces generated by periodic (daily) movements of an electrically conducting layer across the Earth’s permanent magnetic field. Today, we know that solar Extreme Ultraviolet radiation is responsible for ionizing the air and that therefore the ionospheric conductivity varies with the solar cycle [e.g. as expressed by the number of sunspots]; so, observations of the Sun are vital in monitoring and predicting radio communications for Amateurs and Professional alike. Conversely, centuries‐long monitoring of variations of the Earth's magnetic field can be used to determine long‐term variations of solar activity. The talk weaves these various threads from multiple scientific and engineering disciplines together to show the unity of scientific endeavor and its importance for our technological civilization.
Author: Maria Spasojevic, Stanford University Title: Quantifying the Role of Wave‐Particle Interactions in Controlling the Dynamics of the Earth's Radiation Belt
Abstract: The Earth's radiation belts are comprised of highly energetic ions and electrons that are trapped in Earth encircling orbits as a result of the dipolar configuration of the geomagnetic field. The electron flux in the outer radiation belt is particularly dynamic and can vary by several orders of magnitude in the timescale of hours to days. This intense and highly variable radiation poses a significant risk to satellites and astronauts in space. There have been significant advances in the past decade in understanding which physical processes are important in controlling the dynamics of the belts during solar‐driven geomagnetic disturbances. What remains to be quantified is where, when, and under what conditions, specific processes are active and to what degree they individually contribute to the overall balance of acceleration and loss. Increasing attention has been paid to the role of wave‐particle interactions in accelerating electrons up to very high energies. This talk will focus on a particular plasma wave known as whistler‐mode chorus emissions. There is evidence that chorus‐driven acceleration plays a major and possibly dominant role in the reformation of the outer belt in the aftermath of
9 geomagnetic storms. However, a significant confounding factor is that wave‐particle interactions involving chorus can also result in significant losses of electrons due to scattering. We will highlight recent advances in quantifying the role of chorus in radiation belt dynamics.
Author: Philip Scherrer, Prof Physics, Stanford University Title: Viewing the Sun, Inside and Out, with SDO"
Abstract: The Solar Dynamics Observatory (SDO) has been gathering data since its launch (5 years ago). SDO's goals include learning if solar activity is predictable and if so, how to do it. SDO carries three experiments, the Extreme ultraviolet Variability Experiment (EVE), the Atmospheric Imaging Assembly (AIA), and the Helioseismic and Magnetic Imager (HMI). EVE measures Sun‐as‐a‐star spectra in the extreme ultraviolet to monitor wavelengths that are important for space weather impacts on the Earth. AIA obtains images in 7 EUV, 2 UV, and 1 visible bands to study processes in the low corona. HMI measures photospheric motions to enable helioseismology and photospheric magnetic fields to enable connecting the interior to the corona. In this talk I will give a brief overview of SDO and the HMI and AIA data products. I will describe some of the recent findings from HMI concerning the solar interior and evolving magnetic activity in more detail.
Mark Your Calendar
March 20‐22, 2015 SARA Western Conference at Stanford University, Palo Alto, California http://www.radio‐astronomy.org/node/177
April 24 ‐ 25, 2015 Southeastern VHF Society Conference in Morehead, Kentucky www.svhfs.org Subjects will include weak signals VHF to microwave communications. Antennas, Transmitters, Receivers, and SDR methods are typically included. Many receiver and antenna techniques also apply to radio astronomy.
May 6, 2015‐ Nobel Prize recipient Dr. Joseph Taylor, K1JT, will speak at Gloucester County Amateur Radio Club in Williamstown, NJ. The informal session starts at 19:00 and the formal meeting at 19:30. More information on the club can be seen at www.w2mmd.org.
May 15‐17, 2015 Hamvention Dayton, Ohio http://www.hamvention.org/index.php
June 21‐24, 2015 SARA Annual Conference at National Radio Astronomy Observatory in Green Bank, West Virginia www.radio‐astronomy.org/meetings
Do you have an event to share with SARA members? Send information to editor@radio‐astronomy.org to be included in the next issue.
10 Call for Nominations
As required by Section 3 of SARA By‐Laws (see below), this is the official call for nominations for SARA officers and board members. If you are interested in running for office and would like to know more about the positions, please contact a board member or SARA President Ken Redcap (president@radio‐astronomy.org). The requirement to be on the board is to attend the board meetings at the annual meeting and to actively participate in board‐related activities. If you are unable to attend the annual meetings, then the director at large position may be for you. This position is a full board position except that attending the annual meeting is not required.
The following positions will be up for election in June 2015: Secretary, Treasurer, two Director at Large and two regular Directors. If you would like to run for one of the available SARA officer or board positions please send a note to Secretary Bruce Randall (secretary@radio‐astronomy.org) copying President Ken Redcap. Interested persons should review the duties and responsibilities by reading the Operating Procedures found at http://www.radio‐astronomy.org/pdf/operating‐procedures.pdf
Contact information also is listed in the Administrative Info tab on the SARA website (www.radio‐astronomy.org) and in the Administrative section of the SARA journal.
Text from the By‐Laws: SECTION 3: Elections of Directors and Officers will be accomplished by the President placing an initial call for nominations in "The Journal" no less than ninety (90) days prior to the regular scheduled meeting. Two (2) nominations from different members will be required to nominate a member for an office.
No less than thirty (30) days prior to this meeting (in a newsletter issued prior to the meeting), the President will place a notice of the results of the nominations in "The Journal", along with a ballot for the members to use to vote for the nominee of their choice. This ballot will be forwarded to the Secretary for collection and counting at the regular meeting.
SARA Annual Conference at NRAO
2015 Annual Conference Keynote Speaker
Duncan Lorimer from West Virginia University Department of Physics and Astronomy has agreed to be the Keynote Speaker at the 2015 Annual SARA Conference to be held June 20 to 24 at the National Radio Astronomy Observatory (NRAO) in Green Bank, WV. The following excerpt is from WVU website:
I’m an astronomer interested in compact objects (black holes, neutron stars and white dwarfs) which I study using radio pulsars: rapidly spinning, highly magnetized neutron stars. Pulsars are great fun to study and have lead to a lot of exciting adventures over the years. A nice behind‐the‐scenes article describing how this work is carried out can be found here .
11 I arrived at WVU in May 2006 from the Jodrell Bank Pulsar Group where I worked as a Royal Society Research Fellow. Before that I was at Arecibo Observatory (1998‐2001) and at the MPIfR in Bonn (1995‐1998). My research revolves around surveys for radio pulsars and what they tell us about the population of neutron stars. This work is carried out with many collaborators and uses some of the classic radio telescopes around the world. Of particular interest are young, energetic pulsars and binary systems where the orbiting companion is a white dwarf, a main sequence star, another neutron star, and (perhaps soon!) a stellar‐mass black hole.
Call for Papers: 2015 SARA Annual Conference
The Society of Amateur Radio Astronomers (SARA) solicits papers for presentation at its 2015 Annual Conference to be held 21 June ‐ 24 June 2015. Sunday 21 June, will start with an introduction to Radio Astronomy at the Science Center classroom, followed by learning to operate the forty foot radio telescope (1,420 MHz (21 cm). Presentations by SARA members and guests are scheduled on Monday and Tuesday. A High Tech tour of the NRAO facility will be conducted on Tuesday 23 June.
Papers are welcome on subjects directly related to radio astronomy including hardware, software, education and tutorials, research strategies, observations and data collection and philosophy. SARA members and supporters wishing to present a paper should email a letter of intent, including a proposed title and abstract to the conference coordinator at vicepres@radio‐astronomy.org no later than 6 April 2015. Draft of papers are due 20 April and final versions of the papers due no later than 4 May. Be sure to include your full name, affiliation, postal address, and email address, and indicate your willingness to attend the conference to present your paper. Submitters will receive an email response, typically within one week. Guidelines for presenter papers are located at:http://radio‐astronomy.org/pdf/guidelines‐submitting‐papers.pdf
Formal printed Proceedings will be published for this conference and all presentations can be made available on CD
New Website Sections Introduced; Further Enhancements to Come
By Stephen Tzikas
The latest addition to the SARA website is a new tab on the header bar called SARA Sections, in addition to the tabs already there for: Home; Education; Administrative Info; Forum; Projects; Links; Photo Gallery; The SARA Store; and RASDR. The tab for the SARA Sections will bring the visitor to an Introduction page, under which will be six SARA Sections. The purpose of these sections is to create a more intuitive website experience when visitors view the SARA webpage. This will help to enhance the website with a similar feature seen with other national astronomy organizations like that of AAVSO and ALPO. These organizations use sections to organize astronomical research/interest along terms that are more familiar to the public and which offer background and context to everything else on their
12 website. The new sections do not alter any existing content and are envisioned as an ongoing project with further refinements. These refinements will include linking the sections to the Table of Contents for the SARA Journal; linking to the topics in the SARA Listserv; adding more information to the section pages; and information on observing awards. Another phased enhancement will include bringing updates, background, and context to existing SARA links primarily found on the SARA Projects webpage.
One of the potential attractions of having SARA sections is strategic planning. The creation of section strategic plans would help to identify long‐term SARA goals, which would allow potential volunteers to come forward to work on such project goals.
Another attraction of SARA sections is the creation of long‐term databases of member observations that can be available to professional astronomers. SARA does this to some extent now when members submit data to other organizations like Sanford with SuperSID, but having our own unique SARA database could be a new welcomed source of data and standard methodologies to the professional community. SARA databases related to the sectional observations/interests can be created, organized, managed, and stored long‐term based on this "library" structure. SARA would have to determine what is of interest to professional radio astronomers by a variety of methods, such as outreach, survey, the SARA Journal, and working sessions at annual conferences. Once the interest areas of importance are identified, a standard format for data collection would be required. When such a structure is in place, it becomes an attraction for members and non‐members to submit data. SARA could blaze the trail for this. A first step might be to pilot a project database to evaluate the feasibility for establishing a long‐ term database that could be expanded. Member sample data could be compiled to help other observers determine if they are getting a good signal and/or usable data. Additionally, there can be opportunities to collect new types of data using professional equipment via a SARA coordinated effort. For example, the coordination of radio occultation events has not been fully explored. Since radio occultation occurrences are few, having a standard methodology in place before they happen, and pooling the data could be of use to others.
Now that each SARA section is created and posted, we hope we can find section coordinators and members who will be responsible for further enhancements and answering emails from individuals who have an interest in the section and want to join it as their focus within SARA. If you have an interest in becoming a section coordinator please contact me at [email protected]. If more than one person is interested in the same section, the possibilities exist for assistant coordinators and sub‐ section coordinators.
Some days the best part about my job is the chair spins…
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Feature Articles
Slooh Broadcasts with Radio Meteor Audio
By Stan Nelson
Recently, I was contacted by Eric Edelman at Slooh.com about potentially using audio detected by radio using the forward scatter mode. During significant meteor showers, Slooh broadcasts video from observatories located in the Canary Islands, Chile, and Prescott, Arizona. They wanted to add the meteor audio stream that is supported by www.SpaceWeatherRadio.com. The audio feed originates in Roswell, New Mexico and is fed to www.streamguys.com 24x7. They can stream audio for up to 1000 listeners. SARA supported the audio feed with a grant last year. As of January 1st, 2015, the following meteor showers have used the audio as an add-on feature during broadcasts by Slooh:
Orionid Meteor Shower - October 21, 2014. Leonid Meteor Shower - November 17, 2014. Geminid Meteor Shower - December 13, 2014.
Ursid Meteor Shower – December 22, 2014.
Figure 1 is a screen clip from the typical Slooh broadcast during the Orionids.
Figure 1 ~ used by permission - courtesy Slooh.
Tweets from listeners are posted below the video as they arrive. Most are amazed we can ‘hear’ meteors. The concept is explained during segments of the Slooh broadcasts.
Eric used Dave Horne’s Spectrogram to visualize the audio detected by my ICOM R-8500 in the USB mode while tuned to Channel 2 TV (54.24 MHz) video carriers. The receiver is tuned to produce audio from about 300 to 2000 Hz. The blue chart above shows a narrow portion of the audio spectrum. Note the meteor trail in the camera at Prescott. It occurred at the same time as the large Doppler shift seen in
14 the audio in the right side of the spectrum chart. The meteor most likely passed south of Roswell, New Mexico heading west towards Arizona. The TV stations detected are in Mexico. Slooh posts a schedule of broadcasts on their web site at www.Slooh.com. The broadcast’s meteor audio support by SARA is mentioned during various times throughout their broadcast.
Stan Nelson is a native of Niagara Falls, New York. He settled in Roswell, New Mexico in 1968 with his wife and three children. He has been a licensed amateur radio operator since 1961 and currently holds an Amateur Extra Class license as KB5VL. He acquired a 1st Class Radio‐Telephone‐Operators license in 1962 while in the U. S. Air Force. He became involved in the land mobile radio business in Texas. He moved to NewMexico to work for Transwestern Pipeline Company and managed their communications systems for 34 years. He retired in 2002. He became involved in astronomy in the 1970s and served as Roswell’sastronomy club president and provided support to our local planetarium for over ten years. In the last fifteen years he runs an active meteor burst monitoring station which feeds www.SpaceWeatherRadio.com with live audio on a 24x7 basis. He has added numerous related frequencies and activities to monitor additional meteor burst and maintains a site at www.RoswellMeteor.com to share meteor detection data. Stan recently joined S.A.R.A. and attended the recent Western Region conference in Socorro, New Mexico. After that meeting he acquired an e‐Callisto station and TMA from Whit Reeve and is now a regular contributor to the program. Three years ago he was invited to write a feature article on his meteor activity for Monitoring Time. Monitoring Times then invited him to write a quarterly column on radio astronomy which has appeared regularly since December 2010. The magazine is now web‐ based and called Spectrum Monitor.
Credit and copyright: Nick Downes
15 The Big Bang Is Bunk
"The world's firstradio 2Jtt'Ml'lnnnlll' argues that th� ,/e�l$t��c:� of an intergalactic "I'lhealjum atcounls for, • 'AA'CAn,.1'f spectralshifts • need to resort .' ,"religion.•
HaHon Alp by Grote Reber he whole business of Big Bang Creationism is very and an observerof those waves were in relative motion, the shaky and based upon dubious assumptions. The un wavelength at the observer would change. When they are T derlying questions have become lost in the sands of approaching, the wavelength would shorten; when they time and are no longer taught, even in astronomy schools. are separating, the wavelength would lengthen. lately, Big Bang Creationists have far overplayed their hand, This was confirmed experimentally for sound by the Dutch making themselves look like fools. However, because the scientist Buys Ballot in 1845. He' used whistles on steam old-line scientific trade journals are also dominated by re locomotives, the fastest device available in that day. Sev actionary fuddy-duddies, there is not much opportunity for enty-three years later, at age six, I independently discov readers to examine the underlying issues. Accordingly, it is ered the same phenomenon, also using whistles on railway appropriate that these matters be brought forward in a pop locomotives. In retrospect, I had a very clear idea of how it ular scientific magazine. Everyone can examine them at was, but no idea of what it was, much less why. It created a leisure, and I'll be pleased to receive direct comments from schism between mother and small son; mother was no readers. * physicist. (Such is a good storyin its own right. ) Where did this Big Bang idea come from? Three examples of the Doppler phenomenon are shown In 1842, Johann Christian Doppler, a Viennese mathe for the case of light waves (Figure 3). In (a), the double stars matical physicist, predicted that if a source of radiating waves have a substantial range of orbital period from days to years, a randomness independent of the distance from the source to the observer. On the average, the double stars at large Does the extremely thin, hot gas between galaxies-the distance are not rotating any faster or slower than similar intergalactic medium-account for increases in redshiftob pairs nearby. In (b), the rotation of the Sun will be the same served in increasingly distant galaxies? The two galaxies whether viewed from Mercury, Earth, Pluto, Alpha Centau shown here are NGC 5296 and 5297. ri, or the Andromeda Nebula. In (c), the Earth tags along
16 21st CENTURY March-April 1989 43 with motion of the Sun in respect to other stars. Each star and are independent of distance from the observer. The has its own specific motion, and this randomness averages Doppler phenomenon has been used since the last quarter out. The distant stars are not approaching or receding from of the 19th century to study double stars, motions of the the observer any faster or slower than nearby stars. Sun, and rotation of celestial objects. There are always equal In these and other examples, the Doppler phenomenon and opposite redshifts and blueshifts separated by null. The consists of equal and opposite spectral shifts-toward the shifts are very small, from a few to a few tens of kilometers red when recession lengthens the observed wavelength, per second, and are independent of distance. and toward the blue when approach shortens it. These shifts During the 18th century, the French astronomer Charles are separated by a null-a point at which there is no shift- Messier compiled a list of these objects, and the numbers he assigned to galaxies (noted as M1, M2, and so on) are still in use today. The first spectra of galaxies-or white nebulae as they were then called-were made by Vesto How the Big Bang Slipher at the lick Observatorynear San Jose, California, in 1912 (Slipher 1914). By 1925, the list of such spectra had Got Its Start grown to 41 objects. The unexpected finding was that spec tra of white nebulae showed only redshifts. These were 0.2 The Big Bang theory ofthe universe arises from one to 0.6 percent, far larger than any other celestial object. The of the possible solutions to the field equation in Ein nature of these fuzzy patches was a matter of conjecture. stein's theory of general relativity. Einstein's own so George Ellery Hale, director of the Mount Wilson lution specified a universe neither expanding nor Observatory in California, organized a debate on this sub contracting. Sir Arthur Eddington, the British astron ject before the National Academy of Sciences in April 1920, omer who promoted Einstein's theory, was also an but lack of evidence prevented any conclusion. During 1928, advocate for a solution that required the universe to Milton Humason at Mount Wilson undertook a program of expand or contract. measuring the spectra of white nebulae. Again only red After the initial mathematical work on relativity the shifts were found. By 1935 the list ran to more than 150 ory had been done, the Big Bang theory itself was nebulae. Some produced redshifts of 13 to 14 percent, invented by a Belgian priest, Georges lemaitre, im equivalent of a symbolic velocity of about 40,000 km/sec. proved upon by an avowed atheist, George Gamow, During this time, Edwin Hubble, another staff astrono and is now all but universally accepted by those who mer at the Mount Wilson Observatory, was searching for hold advanced degrees in astronomy and the physical Cepheid variable stars, stars that continually dim and sciences, despite its obvious absurdity. brighten with a period from a few hours to weeks. The lemaitre posited a primeval egg about 30 times the longer the period of a Cepheid variable star, the greater is volume of the Sun, containing everything that was to its absolute luminosity. Thus, when the period and appar form the universe. The universe "began'� when the ent luminosity are known, the distance may be secured egg exploded for unexplained reasons. The universe from the ratio of absolute to apparent luminosities. In late has been expanding ever since, according to the the 1924, Hubble discovered Cepheids in the Andromeda Ne ory, and will either continue to expand and cool for bula (M31), which demonstrated that M31 is at a vast dis ever, or else its expansion will eventually be overtak tance, far outside our own Milky Way. The white nebulae en by self-gravitation. In the latter case, itwill collapse are separate stellar systems comparable in size to our own upon itself again. galaxy. This discovery was sufficiently newsworthy to rate a Gamow argued that the egg was made of neutrons story on page 6 of the New York Times, Nov. 23, 1924. and their decay products-a mixture of neutrons, Close collaboration disclosed that the redshifts mea protons, electrons, and radiation-being too hot for sured by Humason were approximately proportional to dis helium nuclei to form. When the bang occurred, the tance as measured by Hubble. According to Hubble, "Hu mess cooled, allowing the formation of helium nu mason assembled spectra of nebulae and I attempted to clei. The relative abundance of hydrogen and helium estimate distances-Humason's adventures were spectac estimated for the universe-11 to 1-is found to be ular" (Hubble 1953). Humason is a name to remember. that expected from Gamow's theory. The theory also pre�icts that the explosion should Redshifts and Irrationality have left behind a universal background radiation. From the very beginning, it was clear the spectral shifts Since a background microwave radiation at 2.7 K has were not the Doppler phenomenon for two reasons: First, undeniably been found, Big Bangers claim that this as astronomers 50 to 60 years ago realized, there were no must be the predicted radiation. blueshifts; second, the shifts were proportional to dis Hubble's law was seized upon by the advocates of tance. As Humason writes in 1931, "It is not at all certain the Big Bang cosmology as supposed proof that the uni large redshifts observed in the spectra are to be interpreted verse is expanding. Some scientists who reject the as Doppler effect. " Hubble in 1937 calls it a "sheer assump Big Bang nonetheless think the evidence for the ex tion" (p. 54). R.H. Baker states in 1930, "The significance of .. pansion of the universe is strong. these remarkable 'apparent' velocities is left open for the -David Cherry present." Fritz Zwicky in 1957 writes, "1 refer here to the origin and to the supposed expansion of the universe... "
44 17 March-April 1989 21st CENTURY (p. 27). Hale in 1931 states that "Other physical causes may netic poles that meet this requirement. The very best place explain a large part of the shift of the spectral lines." Even for observing will be where the band is at the-lowest geo as late as 1962, Otto Struve has misgivings: "But are we sure graphic latitude, giving access to the sky as close as possible that nothing ever happens to a ray of light even if it travels to the celestial equator and then up to the celestial pole. over distances of 10 billion light years?" These places are (in the north) Georgian Bay in south During the 1930s, the cause of redshifts was still an open eastern Ontario, Canada, and (in the south) southern Tas question. Big Bang cosmology had not yet become en mania, Australia. The former looks out on the northern sky shrined as a creed of religious dogma, as some cosmolo and the periphery of the Milky Way, a relatively uninterest gists even admit. For example Peter Goldreich, an enthu ing region. The latter looks out on the southern sky includ siastic Big Bang supporter, writes in 1976, "Although cos ing the galactic center, the Magellanic Clouds, and so on. mologists like to think of their subject as a science, it has This, and adventure in a foreign country made me choose much in common with religion." During recent years, Big the southern one as a start. Bang cosmology has become a form of creationism, with its I arrived in Sydney, Australia, aboard the Orion on Nov. creation date being 5 billion to 20 billion years ago, depend 1, 1954. During 1955-1960, I made preliminary observations ing on the preference of the devotee. to get the feel of things. Cosmic static was getting through In spite of all the evidence against it, the assumption was the ionosphere and was of unprecedented strength. All this made that the spectral shifts were Doppler shifts. Intelli was very encouraging. Accordingly, I decided to set up gent, rational, educated people do not make irrational as properly with an antenna system that could be called a sumptions; there must be some reason for this peculiar hectometer radio telescope, for observations at a wave mental aberration. There is: It is an earlier background length of 100 meters. During 1961 and 1962, I constructed assumption, rarely mentioned, or even implied, that inter an elaborate array consisting of 192 dipoles placed atop 128 galactic space is empty, a void. Once that assumption is wooden poles 80 feet long set 10 feet into the ground. The made, it removes any possibility of light interacting with an overall size was 3,520 feet in diameter, providing a pick-up intergalactic medium. There is nothing left except relative area of 223 acres. The beam could be adjusted to any posi motion. tion in the north-zenith-south plane from south celestial Now, this background assumption is very bad and indi pole to celestial equator. East-west scanning was provided cates a lack of knowledge of elementary physics. Suppose, by rotation of the Earth. At 2,085 kilohertz (khz) the beam once upon a time, intergalactic space was an empty void. was 7.10 in diameter at zenith. I made observations contin Material would immediately begin expanding into it. The uously from Feb. 4, 1963, through May 10, 1967 (Reber 1968, only way this process could be stopped would be for every 1977, 1986). thing to have zero kinetic energy at absolute zero. Clearly, At meter wavelengths and shorter, the radio sky is much this is not reality; however, the assumption was made. Again, like the optical night sky. There is a dark background with rational people do not make ridiculous assumptions; there small sources sprinkled over it. The Milky Way shows up as must be some reason. In this case, the reason is simply that a bright band across the background. I rather expected because astronomers could not find any intergalactic ma something similar to this at hectometer waves; however, terial, none must exist. the situation was completely different and quite unexpect There were dissenters from this ignorant conceit. Ac ed. At 2,085 khz the sky is similar to the daytime optical sky. cording to Hubble, liThe fact that we have not been able to It has a high intensity with maximum intensity at the galactic detect any matter in internebular space does not necessar poles. There are assorted low-intensity patches, like opti ily exclude its existence, even in considerable quantity" cally thick clouds scattered along the Milky Way, which (1937, p. 20). And Zwicky has some acid comments about absorb the background radiation. The lowest intensity is at people who think intergalactic space is empty (1957, p. 25). the galactic center. These clouds are probably low-temper It is clear that I have had little use for Big Bang Creation ature plasma, rather similar to the ionosphere here on Earth. ism, looking upon it as ignorant humbug and voodoo. The high-intensity background lies definitely outside the However, I urge readers not to be too hard on astronomers; Milky Way as shown by absorption patches. Also, assorted they are ordinary people immersed in their own special known radio sources such as in Centaurus, Fornax, Pictor, interests, conceits, and prejudices. and so forth, could be found. Accordingly, the background is at some great distance. The Small Magellanic Cloud My Entry into the Fray seemed to have a small absorption dip. This suggests the How did I get mixed up in all this? Purely by accident presence of low-temperature plasma in the Large Magellan through the back door. ic Cloud similar to the Milky Way. These observations agree By the early 1950s, radio astronomy had become respect with optical findings. Further investigation suggested the able and even popular. The trend was to look for emission background becomes opaque just beyond the source Pic of ever shorter wavelengths, and the science seemed to be tor at 330 megaparsec, or a billion light-years. in good hands. I decided to try for observations at longer wavelengths. Since these long waves must get through the Sourceof High-Intensity Background ionosphere, the best locations for observing will be where What is the source of the background radiowaves mea the electron density is lowest. Examination of a vast amount sured at 144meters? A reasonable guess is that intergalactic of ionospheric data disclosed that there are two bands of space IS filled with free electrons and protons. About one about 350 latitude radius centered on north and south mag- pair per 100cubic centimeters will be adequate. The kinetic 18 21st CENTURY March-April 1989 45 G'rote Reber: Pioneer of Radio Astronomy Grote Reber, a radio engineer and ham radio enthu siast, became interested in radiowaves from space in Antenna 1932, when Karl Jansky at Bell Laboratories first discov Parabolic ered their existence. reflector Reber wrote to leading astronomers, offering them his expertise in radio electronics so that radiowaves from space could be systematically studied. No astronomer would take up his offer; they could not imagine any astrophysical mechanism by which such radio signals could be generated. Perhaps it was just an experimental error or even a hoax, some astronomers told him. At the same time, most radio engineers were indifferent to the problem. As a result, Reber became, on his own, the first-and for 10 years the world's only-radio astrono mer. Reber began by designing a parabolic dish to gather the radiowaves and a radio receiver �o put at the dish's
, Alter John 0, Kraus .... _----- focal point (Figure 1 shows a basic radio telescope de sign). When he solicited bids for construction, Reber Figure 1 found the cost far beyond his reach, so he built it himself HOW A RADIO TELESCOPE WORKS in his yard in Wheaton, Illinois, on weekends. He wag The simplest radio telescope is a parabolic dish and not the first to employ such a device. John Kraus, then an antenna, in combination with a radio receiver. Ra at the University of Michigan, was also following Jansky's diowaves are reflected by the dish, whose parabolic work, and Kraus used a searchlight reflector in 1933 in shape focuses them on a single point above the center an attempt to detect radiowaves from the Sun at 15 mm of the dish, where the antenna is placed. The receiver wavelength. Kraus's experiment was unsuccessful, how-' can be tuned to the wavelength the observerchooses. ever, for want of sufficient sensitivity in the receiver. To produce a radio brightness map of part of the sky Reber was determined to map the spatial distribution for a given wavelength, the dish must cover the area of radio signals on the sky, while also discovering how it by scanning it, in the same way that the eye covers a varied by wavelength. The reflector antenna design al page by readingit line by line. lowed for the reception of different wavelengths by Modern radio telescopes use computers to reas merely changing the receiver at the focus. To get the semble the information into a two-dimensional map maximum resolution, the parabolic dish should be as or picture. big as possible, while the wavelength should be as short as possible. If Planck's law of thermal emission applied,
· 30 20 10 o ��=3�----��-T��------��------� -10 -20 -30
150 120 90 60 30 o 330 300 270 240 210 180 150
Figure 2 REBER'S 1944 MAP OF THE GALACTIC CENTER Reber made the first radio maps of the Milky Way-the equatorial plane of our galaxy. This is his 1944 contour map of the strength of radio emission in the galactic plane at a wavelength of 1.87 meters. The contours are denoted in units of watts per square meter per circular degree per megacycle of bandwith. The peak intensity, enclosed in the contour for 10 units (at center), is the galactic center in the constellation Sagittarius. Source: Reber, "Cosmic Static," AstrophysicalJoumal Nov, 1944, p, 279,
46 19 March-April 1989 21sf CENTURY ..
energy of electrons is equal to an apparent temperature of 3.5 x 1()6 degrees. (The nomenclature is bad because the electron will have a different temperature at every wave length.) The electrons lose.their energy by encounters with protons, which I call free-free transition. Others refer to it as bremsstrahlung or braking radiation (Figure 4). The chances of a close encounter with considerable loss of en ergy is small. Conversely, the chance of a distant encounter with trivial loss of energy is large. Thus, the spectral distri bution will have an inverse intensity-frequency relation. Such is the observed case. The universe has been around a long time. If the free electrons are continuously losing energy by free-free tran sitions, their kinetic energy must be replenished from somewhere. This worried me, and then I had an idea: Per haps the light photons traveling through intergalactic space somehow lose a bit of their energy to electrons. The desi red mechanism is a Compton transition. Each time a photon approaches an electron, the photon transfers some of its
(a) � BIue �.��__ _ i Center Observer Reber poses with his firstradio telescope. Originally built Null of';ass in 1937 in his yard in Wheaton, III., its home today is the Red National Radio Astronomy Observatory at Green Bank, B W. Va., where this picture was taken in 1988. (b) Blue the shorter wavelengths would also be stronger. NUll At a cost of $1,300,Reber built a 31-foot-diameter radio aCen�uri PI� � Me�ry S telescope during the summer of 1937. In the initial ob Red servations, he sought radio emissions from the Sun, (c) Moon, planets, and the brightest stars-first at 9.1 cm (3,300 megacycles) and then at 33 cm (910 megacycles) but none was a source of radio emission. Then in 1939, he moved to 1.87 m (160 megacycles) and at last detected radio emission from sources that were concentrated in Figure3 the Milky Way. When the Earth's rotation caused his THE DOPPLER PHENOMENON scope to pass across the Milky Way, Reber would read In (a), two starsare in orbit about a common center of off the intensity of the radiowaves on a microammeter mass. The spectrum of star A, while it is approaching at 1-minute intervals. the observer, is shifted toward the blue. Meanwhile Because of interference from passing automobiles, the spectrum of star B, while it is receding from the Reber had to confine his observingto the period of min observer, is shifted toward the red. At the moment imum traffic-from midnight to 6 AM. He slept between when there is no receding or approaching motion supper and midnight each night, observed until 6 AM, with respect to the observer, the spectra will not be and then droye toworkatthe Stewart-Warner Company, shifted. where he designed radio receivers. In (b), the spectrum of light reaching the observer Reber reported his first findings in a paper he submit from an approaching limb of the Sun will be blueshift ted to the Astrophysical Journalin 1940.The editor could ed, while the spectrum from a receding limb will be find no reviewer who would defend the paper, and redshifted. The shifts will be the same, regardless of therefore, according to the rules of scientific publishing, whether the observeris sited on Mercury, Earth,Alpha he could have rejected it. Instead, he decided to publish Centauri, or anywhere else. a possibly erroneous paper rather than risk rejecting The motion of the observer rather than the motion what might be groundbreaking work. of the object is illustrated in (c). The small proper Reber not only produced the first radio maps of the motion of the Sun with respect to the starsof its neigh galactic plane (Figure 2), but also correctly identified the borhood is shown. The observeron the Sun or any of mechanism of radio emission as encounters between its planets participates in this motion, seeing blue free electrons and positive hydrogen ions in interstellar shifted spectra for all stars in the forward direction, space. and redshiftedspectra for all starsin the aftdi rection.
20 21st CENTURY March-April 1989 47 energy to the electron and is slightly deflected in its path, a situation shown in Figure 5. The energy loss will be propor tional to the number of encounters, and these in turn are proportional to distance. The energy of a photon is
E = hc/'JI.,where h is Planck's constant, c is the velocity of light, and 'JI. is wavelength. Since h and c are fixed, 'JI. must increase as E decreases. Accordingly, the shift llA/'JI. will be proportional to distance. This is exactly what the optical observations tell us. Clearly, the spectral shifts have noth ing to do with relative motion. Hubble comments, "light may lose energy during its journey through space, but if so, we do not yet know how the energy loss can be explained" (1937, p. 30). The size of the scatter radius in Figure 5 will be on the order of 0.01 arc second at 330 megaparsec, and increases ' with distance. This may well account for the increasingly fuzzy pictures we obtain of increasingly distant objects. Figure4 Another matter is worthy of consideration. As light pho BRAKING RADIATION AND THE tons travel through the maze of electrons in intergalactic INTERGALACTIC BACKGROUND space, some will lose more than average energy and some What Is the sourceof intergalactic backgroundradia will lose less than average. Accordingly, if we start with all tion that becomes "bright" at long wavelengths? In photons having equal energy, a monochromatic line in a teractions between free protons and free electrons, spectrum will broaden as distance increases. But nothing is called bremsstrahlung or braking radiation, would known about this subject. produce the observed background. When a free elec tron passes close to a free proton, the electron emits What Hubble Really Said electrbmagnetic energy. The closer the encounter, Edwin Hubble is usually portrayed, as a promoter of the the shorter the wavelength of the emitted energy. expanding universe, but evidence indicates quite the op-
9
Endview
Source Obeerver Geometric path
Sideview
FigureS 10 DO COMPTON TRANSITIONS EXpLAIN REDSHIFTSt If the free electrons in intergalactic space are continuously losing energy through braking radiation (Figure 4), their energy must be replenished somehow. Perhaps the light photons traveling through space are the source, transferring energy in what is known as the Compton transition. When a photon approaches an electron, the photon transfers energy to it and the photon is slightly deflected in its path. The photon's energy loss will be proportional to the number of encounters; hence, the greater the distance of the source, the greater the energy loss or redshift. Less energetic photons are those with longer (redder) wave-, lengths, and more energetic ones are those with shorter(bluer) wavelengths. Shown here is the line-of-sight path (end view and side view) of a photon undergoing 10 encounters with electrons in intergalactic space, and the net or geometric path of the same photon.
48 21 March-April 1989 21st CENTURY posite. I met him only once for a few minutes one morning �n��__ ------__ in January 1952. I was on my way to Hawaii and located him R.H. Baker, 1930. Astronomy, Urbana, III.: University of Illinois Press. 1st ed., in his office in Pasadena, Calif. My mission was to check up 1930, p. 497; also 3rd ed., 1947, p. 284. on my mother: Could Hubble remember the name of his P. GokIreich, 1976. Focus on the Stars, New York: Shakespeare Head Press, seventh and eighth grade teacher in Wheaton, Illinois? p. 217. G.E. Hale, 1931. Signalsfrom Stars,the New York:Scribners, p. 130. "Yes," he said, "it was Miss Grote. " Apparently my mother E. Hubble, 1937. TheObservational Approach to Cosmology, Oxford University made an impression on him. (I cannot remember the names Press. � 1953."The Law of Redshifts,·Monthly Notices of theRoyal Astronom of my teachers in those grades. ) icalSociety, 113:659. At that time I had no interest in cosmology. However, M. Humason, 1931. "Apparent Velocity-shifts in the Spectraof Faint Nebulae," being a guest, I thought it appropriate to talk about some Astrophysica/,Joumal, 74:35-42. G. Reber, 1968. "Cosmic Static at 144 Meters Wavelength," Journal of the thing interesting to him, Hubble seemed only mildly inter Frank/in Institute, 285:1-12. ested and appeared to feel that everything possible to say _____, 1977. "Endless Boundless Stable Universe," Universityof Tasmania (Hobart)Occ asional Paper No. 9. had already been said many times over. Furthermore, if ____, 1986. "Intergalectic Plasma,· IEEE Transactions on Plasma Physics, future progress were to be made, it would require some P5-14:678-682 (Dec.1986). new and different kind of evidence. Pursuing existing tech V.M. Slipher, 1914. "The Radial Velocity of the Andromeda Nebula," Lowell Observatory Bulletin No. 58. niques would merely lead farther down a dead-end road. I H.S. Shelton, 1953-54. "The Red Shift in Spectra of Distant Nebulae,· Observ asked him what kind of new and different observations atory, April 1953, p. 84; Aug. 1953, p. 159; Dec. 1953, p. 243; Aug. 1954, should be made, but he had no suggestion to offer (Reber p. 169. See p. 171 of last item. O. Struve, 1962. TheUniverse, Cambridge, Mass.: MIT Press, p. 151. 1977, p. 5). F. Zwicky, 1957. MorphologicalAstronomy, Berlin: Springer-Verlag, p. 27. Some years later I stumbled onto a letter Robert A. Milli ��------kan wrote to the astronomer H.S. Shelton on May 15, 1952.
Millikan, who measured the charge of the electron, was a • Readers may write to Grote Reber in care of 21st Century or at General close associate of Hubble. Millikan says: "Dr. Hubble never Delivery,Bothwell, Tasmania, Australia 7030. committed himself to the theory of the expanding uni verse.... Personally I should agree with you that this hy pothesis [Compton collisions] is more simple and less irra tional for all of us. " Now let us see what Hubble says himself:
The disturbing features are all introduced by the recession factor, by the assumption that redshifts are velocity shifts. The departure from linear law of red shifts, the departure from uniform distribution, the curvature necessary to restore homogeneity, the ex cess material demanded by the curvature; each of these is merely the recession factor in another form. These elements identify a unique model among the array of possible expanding worlds, and, in this model, the re striction in time-scale, the limitation of the spatial di mensions, the amount of unobservedmaterial, is each equivalent to the recession factor. On the other hand, if the recession .factor is dropped, if redshifts are not primarily velocity shifts, the picture is simple and plausible. There is no evidence of expan sion and no restriction of time-scale, no trace of spatial curvatureand no limitations of spatial dimensions (1937, p. 63). Figure6 Hubble concludes, "We seem to face, as once before in REDSHIFTED SPECTRA OF GALAXIES the days of Copernicus, a choice between a small finite AT INCREASING DISTANCES universe, and a universe indefinitely large plus a new prin The calcium Hand K emission lines of a galaxy, indi ciple of nature" (p. 66). cated by the vertical arrow in (a), are recognizable in I submit that Hubble was looking for this principle of tired each of the spectra--but are shifted increasingly to ward the red light. A hundred years from now, people will look back on as the galaxy's distance increases (see . the Big Bang Creationists and their antics with laughter, horizontal arrows). The spectrum of galaxy NGC 221 much as we laugh at those who argued over how many at 2.6 megaparsecs (Mpc) distance is shown in (a). angels can dance on the head of a pin! Galaxy NGC 4473 at 28. 8 Mpc is shown in (b)i and a galaxy in the Gemini cluster at 287.5 Mpc is shown in Astronomer Grote Reber, 77, observes and writes in Tas (c). One megaparsecis 3. 26 millionlight years. mania. 22 21st CENTURY March-April 1989 49 PstRotator ~ Antenna Rotator Software Application for Radio Astronomy Whitham D. Reeve
1. Introduction
This article describes the PstRotator application software {PstR}. PstRotator is a Note: Links in braces { } and Windows program used to control antenna rotators (also called rotors) in azimuth references in brackets [ ] are and elevation or just azimuth (figure 1). PstRotatorAz is an almost identical program located in section 9. for users with an azimuth‐only rotator; it has a slightly more compact user interface. PstR costs about US$20 and has built‐in celestial tracking features and interfaces of interest to radio astronomers.
Figure 1 ~ PstRotator (upper) and PstRotatorAz (lower) main user interfaces. Most functions and features are designed for amateur radio but both programs have functions specifically incorporated for radio astronomy. A compact window can be selected (shown later). The main differences between PstRotator and PstRotatorAZ are 2‐axis (azimuth and elevation) versus 1‐axis (azimuth only) control and relay control functions (see text).
2. Antenna rotator control
The basic components used to mechanically point an antenna are a motor for each axis, a position sensor for each axis, mounting arrangements and a controller (figure 2). One motor is required for an azimuth‐only rotator and two for azimuth and elevation. For a given model, the controller usually is matched to the rotator. The controller provides power to the rotators and has a position indicator and momentary switches or buttons to control the azimuth motor (horizontal rotation) and elevation motor (vertical rotation). Most rotators have limit switches or a mechanical stop to prevent over‐rotation. The motors may be ac or dc depending on the model.
23 Azimuth/Elevation Elevation Motor Rotator System Shaft
AZ EL Azimuth/Elevation Controller 279.0 53.5 AC Input LT RTPWR DN UP
Azimuth Motor Multi-Conductor Cables
Azimuth-Only
Rotator System Shaft
Azimuth Controller PWR AC Input LT RT
Azimuth Motor
Multi-Conductor Cable
Figure 2 ~ Manually controlled rotator system block diagrams. Some models use ac and others use dc motors. The multi‐conductor cables between the controller and rotator motor usually have 4 to 6 conductors, some for position indication and others to power the motor. (Images © 2015 W. Reeve)
To control inexpensive rotator systems with a PC, it is usually necessary to modify the rotator controller to include a communications interface such as serial (EIA‐232), USB or Ethernet (figure 3). In most cases, the modified controller retains its original manual control features. Some vendors have a separate (external) EIA‐232 interface accessory for this purpose. In my case, I modified stock controllers with a 3rd party interface as described later. More expensive rotator systems usually have a built‐in communication interface and no modifications are required. After the PstRotator software is installed on the PC, it sends movement commands through the controller communications interface to operate relays that simulate switch or button operation.
24 Azimuth-Only
Rotator System Shaft
Azimuth Controller PWR AC Input LT RT
Azimuth Motor
Multi-Conductor Cable Controller Interface
USB or Serial PC running Ethernet PstRotator or Local Area PstRotatorAz Network
Figure 3 ~ PC‐controlled azimuth‐only rotator system block diagram; a rotator system for azimuth and elevation is similar. The controller interface may be added as an internal modification to the controller or external as shown here. The controller interface is connected to the PC through serial, USB or Ethernet, depending on its capabilities. PstRotator is capable of remotely controlling a rotator over the internet or through a local area network. (Image © 2015 W. Reeve)
3. PstRotator evolution
When I first installed PstRotator, I was very surprised by several things – ease of setup, ease of use, reliability and accessibility of the software developer, Codrut Buda. Prior to using PstRotator I had tried several other rotator control programs and none of them worked well or had any measurable level of software support. With PstRotator I finally had software that worked and was well supported. It did not take me long to realize the high support level, so I decided to ask Codrut for some celestial tracking features including Sun tracking for solar radio. I was surprised when these features were added within a couple weeks of my request.
Although PstRotator originally was designed for amateur radio applications, it clearly has evolved to support radio astronomy. It now includes built‐in tracking for Sun, Moon and all planets as well as pointing to any celestial coordinates by specifying right ascension and declination. In addition, Codrut interfaced PstRotator to Jim Sky’s Radio‐Eyes {RE} program so that any celestial object can be tracked. PstRotator can be setup to work with Radio‐Eyes in two different modes, one simple and one using the more complex Radio‐Eyes Telescope Control Point Program (TCPP). I have extensively tested the simple mode, but discussion of the Radio‐Eyes interworking will have to wait until I have time for further investigation of the TCPP.
Over time, at user request, Codrut added control over LAN and internet (using TCP/IP), satellite tracking and interworking with just about every radio amateur logging program and rotator under the Sun. Also added to PstRotatorAz is local or remote control of several types of relay modules figure 4). The relay control feature is not yet implemented in PstRotator as of this writing (January 2015). I simultaneously run several different installations (instances) of PstRotator. Some operate a Yaesu {Yaesu} rotator through an EIA‐232 interface using a USB‐Serial adapter and some through my local area network (LAN) using an Ethernet‐serial port server. PstRotator co‐exists with itself and all other programs that I have ever tried running at the same time.
25
Figure 4 ~ PstRotatorAz can be used to remotely or locally control relays used for power control or other station control functions. The relay units shown here are KMTronic units compared to an HP calculator. The KMTronic units have 8 relays, each with Form C contacts (Normally Open, Normally Closed and Common). PstRotataor does not yet have the relay control feature. (Image left © 2015 W. Reeve)
The PstRotator user interface has changed a little over the years as features were added. To reduce the clutter of unused features, Codrut added a compact view (figure 5). The user also can customize the “skins” and color schemes. From an operational standpoint, it is only necessary to setup PstRotator for the user’s location, type of rotor controller interface (protocol) and communications method and then specify the type of tracking. The user must specify geographical coordinates so that Sun, Moon and planet tracking will work as expected.
Figure 5 ~ PstRotator user interface compact view. Only the azimuth and elevation are shown.
There are several ways to control a rotor from the PstRotator user interface. These include entering the desired azimuth and elevation into boxes on the main window or clicking on the displayed compass. For terrestrial radio communications, there are several mapping options available and the user only has to click on a map location and the rotor is commanded to point at the appropriate great circle path (both long and short paths are supported).
4. Software upgrades
Upgrades are free and the user may install as many instances of the program on as many PCs as desired without additional license fees. Support for PstRotator is through the PstRotator Yahoo group {Yahoo}, and Codrut regularly publishes a “To Do” list of feature requests from users. Some new features require a couple weeks but most often a couple days. When I started writing this article in early 2014, PstRotator was updated to allow automatic turning of the antenna into the wind or any other preset azimuth when the wind reaches a preset speed threshold. This feature queries the Weather Underground website {WX} to determine wind speeds. If the user has a weather station that sends data to Weather Underground, then that can be selected or the user can select a nearby weather station. This is a useful feature for unattended operation to reduce the chance of wind damage to an antenna. Of course, internet access is required for the weather feature to work.
PstRotator is progressively developed – new features are released immediately. Sometimes this leads to almost daily updates. However, updates are as simple as clicking Check for Updates in the Help menu. This
26 automatically updates all instances of PstRotator that have been setup using the Multiple Instances feature. Updates are manually initiated by the user and all previous settings are retained so there are no surprises. If there are bugs in PstRotator, I am not aware of them after about six years of use. Occasionally, a new feature has a minor problem but these usually are fixed within 24 hours of a trouble report.
5. Rotor controller interfaces
Most of my rotatable antennas use an azimuth‐only rotator. I modified the factory controllers with the Easy Rotor Control (ERC) controller interface designed and sold by Rene Schmidt {ERC}. The ERC was another nice revelation in reliability and product support. The ERC is a small printed circuit board (PCB) with a microcontroller and several relays (figure 6) that can be installed in many of the Yaesu controllers. Because the Yaesu controller power supply is isolated from the metal chassis and ground and the ERC is not, I also installed a small 12 Vdc power supply and transformer for the ERC, making a simple self‐contained installation.
Figure 6 ~ Easy Rotor Control printed circuit boards. The model ERC (left) and ERC‐3D (right) are installed in Yaesu controllers at my observatory. Since my installation, the vendor has upgraded the two models to ERC version 4 and ERC‐M, respectively. The ERC board dimensions are approximately 79 x 54 x 20 mm. (Images © 2014 Ing.‐Buero Alba de Schmidt, www.schmidt‐alba.de, used with permission)
I have installed the ERC in Yaesu G450‐A and G800‐SA enclosures (figure 7). I also have a Yaesu G5500 controller used for azimuth and elevation. For this I used the ERC‐3D, which is similar to the ERC but is external and has two control channels and an optional digital display. The ERC‐3D is no longer available and has been replaced by the ERC‐M, which provides azimuth‐only, azimuth and elevation or dual‐azimuth functions. I also use the SPID Alfa RAS rotator {SPID} but it has a built‐in communications interface.
6. PstRotator Setup
When setting up PstRotator it is necessary to select the correct communications protocol. There are fewer rotor control protocols than rotor types – for example, a popular protocol is the Yaesu GS‐232, and it is used by many non‐Yaesu rotor controller interfaces. The PstRotator setup menu lists controllers by name so the user does not need to know the actual protocol, only the controller type.
27 Figure 7 ~ G450‐A controllers (upper‐right and lower‐left) and G800‐SA controller, all modified with internal ERC modules and in active service. Only the G800‐SA is shown tracking the Sun. Also seen in this picture is the 5‐port Ethernet switch that handles LAN traffic for the equipment. (Images © 2015 W. Reeve)
During setup it also is necessary to specify the communication method and associated port. For example, a PC serial port may be used and it is necessary to specify the associated COM port number. For TCP/IP it is necessary to specify the IP port number (or use the default port). The various settings are grouped under the Communications menu (figure 8).
Figure 8 ~ Communications setup dropdown menu reveals the various communication methods supported by PstRotator.
PstRotator can be setup in Server and Client modes to allow remote control over a LAN or the internet. For the client/server configuration, PstRotator is setup on one PC to run as the server (the PC to which the rotor controller is connected) and on another PC as a client. The client then controls the rotor through the remote server PC. Instead of a PC, the remote server can be a terminal server or Ethernet‐serial port server such as the B&B Electronics VLinx ESP900‐series Ethernet Serial Servers. This is the configuration I use in Anchorage to control an HF log periodic antenna rotor over a wireless LAN.
7. Celestial Object Tracking
My installations use only a fraction of PstRotator’s capabilities. The ones I use are all related to celestial tracking, so the remainder of this review will describe only my applications. As mentioned earlier, PstRotator can track the Sun, Moon and all planets and it also works with Radio‐Eyes. For its built‐in tracking to work properly, PstRtotator needs an accurate time‐of‐day clock and the station’s geographical coordinates. There are many programs available to synchronize a PC’s clock (for a description of some programs, see [Reeve]). Station latitude and longitude are easy to obtain using Google Earth or online calculators.
In my Anchorage observatory, I mainly use PstRotator to track the Sun. During mid‐summer, the tracking spans true azimuths from about 34° to 325° and elevations up to 52° (figure 9). During mid‐winter the Sun is tracked from as little as about 145° to 213° true azimuth with a maximum elevation of 6° around the winter solstice. PstRotator’s built‐in Sun tracking is enabled by selecting Sun on the Tracking menu and then selecting the Tracking Mode radio button on the main window. PstRotator can remember the tracking mode and will resume tracking if it is restarted.
28 Maximum daylight rotation range of Figure 9 ~ Reeve station solar tracking Sun during summer: 291° geometry throughout the year showing Maximum elevation: 52° June 20 the variability in azimuth and elevation at 325º 34º northern latitude. (Images © 2015 W. Reeve)
As the Sun moves across the sky, PstRotator commands the rotor to move accordingly. The Sun Tracking setup menu includes a setting to start tracking at a Sun elevation of –9° to Reeve Observatory +45° with respect to the horizon. For Station Coordinates: Summer arc 61.19925N : 149.95655W HF observations I usually start tracking –5° (before sunrise) and stop –5° (after sunset). This has helped me
Beam Pattern of capture several solar HF radio bursts Sun-tracking after sunset during summer (the Sun 8-element Log Periodic Antenna does not drop lower than about 5° below the northern horizon at Anchorage during mid‐summer). Minimum daylight rotation range of 213º Sun during winter: 68° 145º Maximum elevation: 5° Most of the time I use PstRotator’s December 20 Parking feature to park the antenna Winter arc at 90° azimuth so that after sunset the antenna automatically rotates back around to the east, making it ready for the next sunrise.
The resolution of the rotor movement can be specified. I have both PstRotator and the associated ERC controller set to 1° resolution. The resolutions can be different but the lowest one determines the system resolution. With this setting PstRotator sends a rotate command every 1° when tracking the Sun resulting in antenna movement approximately every 4 minutes or so. PstRotator is capable of tracking to within 0.1° but this is of little use if the rotor and its controller do not support such fine resolution (the resolution of the Yaesu rotators is around 5°) or the antenna has a wide beamwidth. Earth‐Moon‐Earth (EME) communications and satellite tracking use very high directivity antennas and high resolution rotator systems, so very fine resolution is needed for those setups. However, I use log periodic antennas with 50~60° beamwidths in my solar radio installations, so even 1° resolution setting is technically farfetched.
Although I use PstRotator to automatically track the Sun every day, I often interrupt this schedule for Jupiter radio observations. However, I use a different strategy. Instead of tracking Jupiter, I use a fixed azimuth. Because of high RFI levels at my Anchorage observatory, I usually determine Jupiter’s azimuth range for a predicted pass (enhanced Io‐A, Io‐B or Io‐C) using Radio‐Jupiter Pro3 prediction software and then manually rotate the antenna to an azimuth near the middle of the pass but offset as needed to minimize the RFI. In other words, I try to point a null in the antenna pattern toward the RFI source while keeping Jupiter in the main beam. Of course, there are many times when I cannot find a compromise azimuth that both reduces RFI and has Jupiter in the main beam but this strategy has improved my success, especially during summer when RFI levels are lower.
29 8. Conclusions
PstRotator and PstRotatorAz are application programs used to control almost any type of antenna rotator through a serial, USB or Ethernet interface. Unlike other rotator control programs, PstR and PstRAz are very reliable and have numerous useful functions directly related to radio astronomy.
9. References and web links
[Reeve] Reeve, W., Maintain Your Time, Radio Astronomy, Society of Amateur Radio Astronomers, May‐June 2012
{ERC} Easy Rotor Controller: http://easy‐rotor‐control.com/ {PstR} PstRotator and PstRotatorAz: http://www.qsl.net/yo3dmu/index_Page346.htm (RE} Radio‐Eyes: http://www.radiosky.com/softwarehome.html {SPID} SPID Alfa rotator: http://www.spid.alpha.pl/english/01.php {WX} Weather Underground: http://www.wunderground.com/ {Yaesu} Yaesu rotator: http://www.yaesu.com/?cmd=DisplayProducts&DivisionID=65&ProdCatID=104 {Yahoo} PstRotator Yahoo group: http://groups.yahoo.com/neo/groups/PstRotator/info
Author: Whitham Reeve is a contributing editor for the SARA journal, Radio Astronomy. He worked as an engineer and engineering firm owner/operator in the airline and telecommunications industries for more than 40 years and has lived in Anchorage, Alaska his entire life.
30 Cassiopeia: A Scintillation Observed by Radio Jove Participants Dave Typinski, AJ4CO Observatory Thomas Ashcraft, Heliotown Observatory Wes Greenman, LGM Radio Alachua
November, 2014
In December 2013, Dave Typinski recorded a spectrogram with some ghostly sweeping features in it. Discussion with the Radio Jove Spectrograph Users Group (SUG) suggested that since there was a CME impact at the time, the weird spectrogram was probably a result of a geomagnetic disturbance.[1] In October 2014, Typinski again noticed more of these features appearing almost every other night in his spectrograms. More discussion within the SUG ensued, whereupon the emissions were oh‐so cleverly dubbed “weird night time events” or WNE’s. Thomas Ashcraft started noticing WNE’s in his spectrograms, as did Wes Greenman. We all scratched our heads. There were no coronal mass ejection (CME) impacts, but the Sun was rather active. “What are these things?” we all wondered.
Figure 1 – The spectrogram that started it all, a WNE observed in December 2013. Horizontal bands are radio stations, the bright angled trace is a radar sweep. Cas A scintillation is seen as a series of nearly vertical wispy, somewhat curved and angled sweeping features. The antenna array was steered to zenith at this time.
Ashcraft suggested that maybe we were seeing Cassiopeia A or Cygnus A scintillation. He noted the similarity of the WNE’s to scintillation events observed by the KAIRA research instrument in Finland.[2] At the same time, Dr. Francisco Reyes was working out the transit time, flux density, and locations of Cas A and Cyg A and provided strip charts of Virgo A beam transits he made in 1991‐93 using the large 26 MHz array at the University of Florida Radio Observatory. These showed that sometimes the scintillation was strong and other times it was nearly absent. Dr Reyes also noted that since Cyg A transits a bit earlier than our observed WNE’s, Cas A scintillation was the best candidate for the observed WNE’s. He suggested that Typinski steer his 8‐element array toward Cas A, which was done on October 30. Lo and behold, the wispy, sweeping features appeared much stronger (Fig. 2 below) and looked very similar to the KAIRA spectrograms. The mystery was solved: the weird nighttime events were scintillation of Cas A’s emission. To our knowledge, this is the first time the dynamic spectra of Cas A scintillation in the HF band has been intentionally observed by an amateur radio astronomer.
31
Figure 2 – Cas A scintillation observed by Dave Typinski (High Springs, Florida) on 30 Oct 2014 with an 8‐element terminated folded dipole (TFD) array, the dual polarization radio spectrograph (DPS), and two Jove receivers. The antenna beam was steered to 0° azimuth and 60° elevation. Cas A transited at 0221 UTC (represented by red arrows). 20 MHz half power beam width (HPBW) is 15° NS and 35° EW; directivity for emissions with random polarization (such as Cas A) is approximately 14 dBi. Top: Spectrogram with time on the horizontal axis, frequency in MHz on the vertical axis (this spectrogram has 300 frequency channels), and signal power represented by color. Scintillation is seen as nearly vertical sweeping lines. The horizontal streaking is interference from radio stations. Middle: Single frequency (~20.1 MHz) strip chart with time on the horizontal axis and antenna temperature on the vertical axis. Bottom left: Radio Eyes plot at observing time. Bottom right: Radio Jupiter Pro sky view at observing time. Ovals represent the array’s 20 MHz HPBW.
32
Figure 3 – Cas A scintillation observed by Wes Greenman (Alachua, Florida) on 01 Nov 2014 with the dual dipole Carr array (1½‐inch diameter aluminium tubing element arms cut for 20.7 MHz with 25‐foot element spacing) and the FSX‐1 radio spectrograph. Beam was steered to 0° azimuth and 60° elevation and the array directivity was about 8 dBi.
Figure 4 – Cas A scintillation observed by Thomas Ashcraft (Lamy, New Mexico) on 07 Nov 2014 with a Radio Jove dual dipole array and the FSX‐4 radio spectrograph. Beam was steered to zenith and the array directivity was about 8 dBi.
Cas A scintillation explains why we have not observed such phenomena at other times of the year. It is visible only when Cas A is in the antenna beam, far enough from the Sun to avoid daytime band noise, and not so far into the night that the ionosphere has smoothed out to a large extent. We suspect there is perhaps a two or three month window where observation of Cas A scintillation is possible for the 8‐element terminated folded dipole (TFD)array. We also suspect a possibility of observing scintillation in the emission from Cygnus A. Observational checks of these ideas will have to wait until next year when Cas A and Cyg A are in the proper positions relative to the Sun.
Cassiopeia A is a supernova remnant roughly 11,000 light years away (about 3.4 kiloparsecs). Discovered by amateur radio astronomer Grote Reber in 1947, it has a 20 MHz flux density of 65,000 Janskys, similar in strength to weak Jovian emission, and is the strongest radio source outside our solar system.[3]
33
Figure 5 – Cassiopeia A in three frequency bands. Infrared data from the Spitzer Space Telescope are colored red; visible data from the Hubble Space Telescope are yellow; and X‐ray data from the Chandra X‐ray Observatory are green and blue. The central neutron star is the tiny turquoise dot at center of the shell of gas. Image and text credit JPL‐Caltech.[4]
Cas A is located at right ascension 23h 23m and +59° declination. To find the proper beam elevation, we have:
Source elevation at 0° azimuth (northward) = 90° – source declination + observer latitude
Typinski’s latitude is 30° N, so his array’s beam was steered northward to 60° elevation. A few degrees either way for small arrays with their relatively large half power beam widths (HPBW’s) makes no practical difference, so we went to the nearest 5° elevation increment.
Since Cas A is a point source, it is very difficult to detect in the HF band with modest antenna arrays despite its high flux density. The strip chart in Figure 2 shows the variations for this particular observation are only 1 dB or so above the galactic background with an 8‐element array. While the scintillation observed with Wes Greenman’s Carr array steered to 60° N elevation (Fig. 3) shows up fairly well, the scintillation observed with Ashcraft’s dual dipole Jove array steered to zenith (Fig. 4) is just barely distinguishable in the spectrogram. Quiet observing conditions help greatly, especially when using small arrays. Even so, single‐frequency (Jove receiver, strip chart) observers using a dual dipole array would have great difficulty seeing and recognizing scintillation in Cas A emission.
In fact, if the scintillation did not exist, we would not have been able to recognize Cas A emission even with the 8‐element TFD array. It would be difficult unto impossible to see a bell‐shaped curve in a strip chart as Cas A moved through the antenna beam. To find out how long a radio source takes to cross an antenna’s beam, we have:
beam width in degrees Beam transit time in hours = 15°/hour × cos() declination
For the TFD array’s 35° east‐west HPBW, Cas A crosses the beam in about 4 hours 30 minutes. For the roughly 70° east‐west HPBW of the Jove dual dipole array, the time is 9 hours. These long transit times make it nearly impossible to separate Cas A’s emission from the diurnal variation in galactic background. Scintillation,
34 however, acts on a much shorter time scale – on the order of a few minutes – making it discernable in a strip chart or spectrogram.
Radio scintillation is just like the twinkling of a star in the optical spectrum as starlight is refracted by density variations in the Earth’s atmosphere. One cause of radio scintillation is spatial and temporal dynamic variation of the charge density within Earth’s ionosphere. There may be other causes as the emission passes through the interstellar and interplanetary mediums (ISM and IPM). We restrict the following discussion to the terrestrial ionosphere; however, similar phenomena may be occurring to some degree in the ISM and/or IPM, possibly with different intensities and on different time scales.
The ionosphere is anything but flat and smooth; it is more like lumpy oatmeal. Charge density variations (lumps in the oatmeal) move around within the ionosphere and can act like lenses for radio waves, intermittently focusing more of Cas A’s radio emission on the aperture of a ground‐based HF radio telescope, briefly increasing the power received by the antenna. We believe this is what causes the nearly vertical sweeping streaks in the spectrograms in Figures 1 through 4. As the ionospheric disturbances move around, once in a while the lens effect sweeps past Cas A from the observer’s viewpoint, briefly increasing the received signal strength. The streaks in the spectrogram are not perfectly vertical because ionospheric effects are frequency dependent – at any given time, a good ionospheric lens for Cas A at one frequency may not be so good at another frequency.
A disturbed ionosphere can cause the observed scintillation. High solar activity or a CME impact will stir up the ionosphere. However, sometimes when the Sun is active, Cas A scintillation is not observed. The fine structure and variability of the ionosphere with solar activity is very much a field of current research. Instruments like the LWA and LOFAR are observing ionospheric scintillation in the emission from distant sources like quasars. Cas A scintillation is one probe of the ionosphere’s dynamics.
[1] http://www.radiojove.org/SUG/
[2] http://kaira.sgo.fi/2012/10/ionospheric‐scintillation‐with‐kaira.html
[3] Baars, et al., The Absolute Spectrum of Cas A, A&A (1977)
[4] http://www.spitzer.caltech.edu/images/1445‐ssc2005‐14c‐Cassiopeia‐A‐Death‐Becomes‐Her
35
Dave Typinski is a professional businessman and amateur scientist who has been tinkering with things electrical and mechanical since he was old enough to hold a soldering iron and a Crescent wrench. He is an active member of the Radio Jove project, operating AJ4CO Observatory in High Springs, Florida.
Thomas Ashcraft operates a radio and optical observatory in north central New Mexico. His primary observing targets are transient luminous events (sprites), Jupiter, fireballs, and the Sun.
Wes Greenman is a retired engineer from the University of Florida Astronomy Department. He notes, "We were involved with Jupiter research for much of that time. The Radio Jove program enables me to continue this research. Besides, it's fun."
36 Leap Second to be Added in 2015! Whitham D. Reeve
Introduction: Leap seconds are inevitable because of the way time is defined worldwide, but that has not stopped the news media from getting hysterical about it [USA Today]. The last leap second was introduced 30 June 2012 and the next one will be 30 June 2015. I wrote about the 2012 event in [Reeve‐1] and have repeated some of the information from that article below. I also explored some of the problems and solutions associated with keeping proper time in amateur radio astronomy in [Reeve‐2, Reeve‐3].
Leap seconds are used only when needed as determined from measurements. A leap second is added or subtracted every so often to keep Universal Time (UT, in particular, UT1) and Coordinated Universal Time (UTC), synchronized within less than ±0.9 second. The UT time scale is based on Earth’s rotation rate, which changes slightly over time, sometimes it speeds up but most often it slows down, and the leap second compensates for this variation.
Embedded in UT is the mean astronomical second, which is defined as 1/86 400 of the mean solar day. It is determined by precise measurements. On the other hand, UTC, which is the legal basis for timekeeping and the time reference used in most countries, is an atomic time scale based on the emissions frequency of cesium atoms when certain electrons change state. Embedded in UTC is the definition of the second, which is 9 192 631 770 periods of the radiation emitted from cesium 133 when it is under specified environmental conditions (a frequency of about 9.193 GHz).
2015 Leap Second: The International Earth Rotation and Reference Systems Service (IERS) issues Bulletin C every six months to announce either a time step in UTC (leap second) or to confirm that there will be no time step at the next preferred date. The preferred time and dates for leap second insertion or deletion are midnight 30 June and 31 December but 31 March and 30 September also may be used if necessary to stay within the 0.9 second difference requirement mentioned above. IERS published Bulletin C49 on 5 January 2015 announcing a positive leap second in June 2015 with the following sequence of the UTC second markers (see also figure 1):
2015 June 30 23h 59m 59s 2015 June 30 23h 59m 60s 2015 July 1 0h 0m 0s
30 June 2015 30 June 2015 01 July 2015 23:59:59 23:59:60 00:00:00
Fig. 1 ~ A leap second will be inserted to retard UTC at the end of June 2015. The clock shown here is conceptual and based on the UTC time scale, so the leap second will be added at different local times depending on the user’s time zone. It is unlikely that any real clock will show the digits “60” in the seconds field as shown here. (Image © 2015 W. Reeve)
All leap seconds to date have been positive. Thus, the difference between International Atomic Time (TAI) and UTC has increased over time. With the next leap second, the difference will be
From 2012 July 1, 0h UTC, to 2015 July 1, 0h UTC: UTC – TAI = –35 s From 2015 July 1, 0h UTC, until further notice: UTC – TAI = –36 s
37 Conclusions: Exactly three years after the insertion of a leap second at midnight on 30 June 2012 another leap second will be added to the list. In keeping with the tradition promoted by an alarmist news media, many time users worldwide will be restocking their underground shelters with canned chili, bottled water and flashlight batteries. Meanwhile, the Sun will continue to rise in the east and set in the west as it has since the beginning of time as we know it.
References: [Reeve‐1] Reeve, W., Is Time Broken (Or, Will It Be Y2K All Over Again), Radio Astronomy, July‐August 2012 [Reeve‐2] Reeve, W., Time Differences in Charted Solar Observations at High Frequencies, Radio Astronomy, July‐August 2012 [Reeve‐3] Reeve, W., Maintain Your Time, Radio Astronomy, May‐June 2012 [USA Today] Griffin, A., Computer chaos feared over 2015's leap second (http://www.usatoday.com/story/tech/2015/01/08/computer‐chaos‐feares/21433363/) [IERS] Bulletin C49, International Earth Rotation and Reference Systems Service, 5 January 2015 (http://hpiers.obspm.fr/iers/bul/bulc/bulletinc.dat)
Above‐ Keynote Speaker Jill Tarter answers questions from the audience at the 2009 SARA Annual Conference at Green Bank, West Virginia. Ms. Tarter’s husband Jack Welch will be presenting a paper at the 2015 Western Conference at Stanford University in Palo Alto, California.
38 RASDRviewer PULSAR FEATURE DESCRIPTION Paul L. Oxley
ABSTRACT – This document describes the proposed process for capturing a pulse from a Pulsar. The objective of the process is to be able to display and record the pulse profile1 during the period when the Pulsar is within the beam width of the antenna. The process works in near real time on a high end Windows PC. The process uses In phase and Quadrature (I & Q) samples that are presented to a Fast Fourier Transform (FFT). The FFT output is entered into an accumulation matrix of time verses frequency bins. The accumulated values are coherently integrated to improve the Signal to Noise Ratio (S/N). The Time difference between each FFT is varied to allow the selection of the appropriate slope (ΔT/ΔF) that will cancel the dispersion present in the Pulsar data. For the Dispersion Process, the user needs only to supply a range of expected dispersion values and a Signal to Noise Ratio criteria that defines a usable signal.
Further processing is accomplished using a lower frequency clock rate to identify both the fundamental frequency of the pulse and its phase. The low frequency clock is locked to this phase to allow further coherent integration (Folding). For the low frequency processing the user supplies a range of expected pulse rates.
Although this procedure is developed for implementation in the RASDRviewer software, it is generally applicable in those situations where software control of the sample rate and samples per frame are both available.
INTRODUCTION –The author is developing a new Pulsar capture/analysis feature for the existing RASDRviewer software 2 which is the companion to a small single chip receiver of interesting radio astronomy spectrum. The receiver is named the Radio Astronomy Software Defined Receiver (RASDR)3. The bandwidth of the receiver can be software configured in steps up to 28 MHz. The sample rate of the receiver can be software configured over the range of 1.5 Million Samples per Second (MS/S) to 32 MS/S. The receiver uses a Cypress FX3 chip to provide a USB 2 or USB3.0 interface to the user’s Personal Windows Computer where the RASDRviewer software resides. The receiver covers a range of frequencies from 300 MHz to nearly 3 GHz.
Pulsar experiments are of interest in the portions of this range where a good signal to noise ratio can be obtained. Particular interest is in the frequencies where the regulatory bodies have reserved spectrum for Radio Astronomy including 322 to 328.65 MHz, 406.1 to 410 MHz, 608 to 614 MHz and 1420 to 1427 MHz. Several Amateurs have built dish antenna systems that are sized for studying the 1420 MHz range. These antennas likely can be modified for the lower frequencies by the application of a suitable feed. The RASDRviewer software operates on a near real time basis to produce representations of the received signal in a nearly continuous manner to produce Fast Fourier Transforms (FFTs) of the incoming data. Blocks of continuous data samples are gathered into frames and presented to the FFT-W
1 See Lorimar, D.R. and Kramer, M., HANDBOOK OF PULSAR ASTRONOMY, Copyright 2005, Page 8 for a description of a Pulse Profile. 2 Paul L Oxley, et al, RASDRviewer – RASDR2 Control and Analysis Software, SARA Proceedings of the 2014 Annual Conference, Copyright 2014 SARA. 3 See various publications in the SARA Journal and Proceedings.
39 software. During the period of time that the FFT is being produced, the incoming data stream is ignored. Once the FFT process completes, the process repeats on the next frame.
The RASDR receiver contains a Temperature Compensated Crystal Oscillator (TCXO) which controls the timing of the sampling of the data and the Phase Locked Loop (PLL) oscillators that are used for down conversion of the signal. The TCXO can be phase locked to an external 10 MHz frequency reference such as a GPS receiver which improves the frequency accuracy. In phase (I) and Quadrature (Q) samples are produced by the receiver chip. The I and Q samples are placed in a First In First Out (FIFO) buffer on the FX3 chip. The FX3 chip gathers these I and Q samples into packets for transmission via the USB interface.
TIMING – Timing is obtained by counting the packets that arrive from the USB interface. Each packet contains a number of Bytes that is determined by the PC’s configuration. It can be either 512 or 1024 Bytes per packet. The Sample data that arrives in the USB3 FIFO buffer is precisely timed by the TCXO on the RASDR boards. Since the number of bytes and the sample data rate is known, the packet arrival rate is known. The following table shows some typical calculations of the packet rate and packet duration. USB Interface & Packet Counter Sample Rate 10 32 10 32 MS/S Packet Size (Set by Machine) 512 512 1024 1024 Bytes/Packet Bytes/Sample 4 4 4 4 Samples / Packet 128 128 256 256 Packet Rate 78,100 250,000 39,100 125,000 Packets/Sec Packet Duration 12.80 4.00 25.60 8.00 uS/Packet
The first and third columns in the table shows the maximums for a USB2 interface. The second and fourth columns are the maximum for a USB3.0 interface.
The packet duration numbers are used in the calculation of the number of packets necessary to time both the High Frequency (Dispersion Equalization) and the Low Frequency (Pulse Recovery) portions of the process. Using the second column as an example, if a time slot width of 12 milliseconds is needed for timing, it would require a count of 3000 packets.
ACCUMULATION OF SAMPLES INTO FRAMES – The data from the packets are assembled into frames of user specified N = 2X length (X = 1, 2, 3, etc.). An FFT is performed on each frame which generates (N) complex (I & Q) frequency bins on each frame. The assembly process is repeated until N frames are available to complete an N X N matrix of FFT bins. . The spacing of the frames is set to accommodate the times necessary for a given Dispersion Measure (DM) value. The N X N matrix is stored in a circular buffer for further processing.
SETTING DISPERSION MEASURE (DM) VALUES FOR TESTING – The DM value is changed by selecting a packet count value and sample rate that will produce a slope (ΔT/ΔF) in the matrix for the selected N bins. The following formula is used to convert a DM to a slope:
40 3 4 ΔT/ΔF = 8.297616 DM /FCtr Where ΔF is in MHz, ΔT is in υS and FCtr is in GHz
COHERENT INTEGRATION OF THE MATRIX – The frame generation process is repeated to accumulate additional data for integration to improve its Signal to Noise (S/N) ratio. The integration process uses complex calculations to retain the quadrature relationship of the data in each FFT bin. A Signal to Noise (S/N) test is performed to determine when the data is adequate for further processing by succeeding program steps. The test involves the comparison of the peak values of a frequency bin to the mean of all frequency bins. When the peak value exceeds the mean by X dB, the S/N is deemed adequate. X is a user specified variable that will be determined by experience running the system. The test is continuously repeated for several successive frames to insure that a valid S/N is available.
DE-DISPERSION PROCESS - The de-dispersion involves the collection of data from the FFT frames that correspond to the amount of delay correction needed for each FFT frequency bin. The de-dispersed data can be viewed as a representation of the original pulse generated by the Pulsar where all frequencies were pulsed simultaneously.
The FFT matrix is used by the De-Dispersion process to perform a cancellation of the delay distortion. Each of the lines in the matrix contains data from a different point in time. The process picks one bin from each line to form the de-dispersed data.
The separation in time between each line is based on the Dispersion Measure (DM) currently being tested. Initially, the DM is set to the lowest value within a range of values supplied by the user. The DM is incremented until at least two of the lines contain a bin which meets the criteria for a valid S/N ratio. Each time that the DM being tested is changed, the accumulators in the matrix are reset to avoid having mixed data from multiple DM values.
Figure 1 Determining Slope of the Dispersion Once two or more values are valid, a slope ΔT/ΔF is calculated. An example of the slope calculation is shown in Figure 1. The slope is used to set a new DM test value, the accumulators reset and retested after an integration period.
4Derived from Lorimer, D.R. and Kramer, M, Handbook of Pulsar Astronomy, Copyright 2005, Appendix A2.4
41
Figure 2 Dispersive Lock Condition Once all of the lines contain one bin with valid S/N ratios, the De-Dispersion process is locked. This condition is shown in Figure 2.
During the Dispersion Lock state, no further changes are allowed in the Sample Rate, Frame Length and Frame Timing. This is necessary to allow the continuing cancelling of the dispersion for the low frequency processing.
The Matrix is continuously displayed for the duration of the De-Dispersion process. It optionally can be recorded to disk. Once the De-Dispersion process is locked, the dispersion matrix display is held at its last value. This is necessary since the matrix accumulators will be reset for each change of the Low Frequency Time Slot Width (W).
LOW FREQUENCY (PULSE) PROCESS –The low frequency data is stored in an accumulator 1 X M array. The accumulation of the data occurs during the period of time between the start and end of the Time Slot. A mean value of all frequency bins present in the de-dispersed data is added to the accumulator for each frame that is processed. At the end of the time slot, the accumulated value in the array is held for additional processing the next time that that time slot is processed. This is a continuous integration process. The accumulation process moves on to the next time slot until all M time slots have received data. The accumulators for the mean calculations are reset to zero whenever a user request is received, or a parameter such as the time slot width (W) is changed.
OBTAINING A GOOD S/N RATIO – To obtain a good S/N, it is necessary to allow the continuous integration to operate long enough to lower the random noise from the mean value in each time slot. To determine when sufficient time has lapsed, a calculation is made of the mean of M sequential time slots. The mean of each of the M time slots is compared to the mean of all time slots. When more than one of the M time slots is above the mean of all time slots by a user defined margin of X dB, the S/N is declared as sufficient for further processing. For this step to be successful, the width W of each time slot and the number of time slots M must be set to values that will show the differences between a time slot with a high level pulse present and others without the pulse present.
OBTAINING THE FUNDAMENTAL FREQUENCY OF THE PULSE – The user specifies a range of expected pulse rates to test. In some cases, the user may know more precisely what pulse rate to
42 expect from previous observations or a published catalog. In those cases, the search time can be greatly reduced. To search for the fundamental frequency of the pulse, the highest pulse rate R is tested first. A value of W is calculated from the following formula: W = 1/2R
This establishes the condition where alternate time slots will contain the pulse peak with the other time slot containing the valley for the condition when the pulse rate fundamental frequency is detected. For this processing, the number of time slots M should be set to have multiple time slots processed simultaneously. For convenience in processing, the number of time slots M will be set to 9. TS 0 TS1 TS0 TS1 TS0 TS1 TS0 TS1 TS0 High Low High Low High Low High Low High Figure 3 – The alternate Time Slot condition for fundamental frequency lock
The pulse rate R is decremented from the maximum until the alternate time slot condition is met. This condition is shown in Figure 3. The accumulators are all reset with each change in R. It should be noted that for each change in R, the processing must wait for the necessary integration time for a good S/N. Since the value of M was set to 9, the exit test for the fundamental frequency decrement process is 5 highs and 4 lows, or 5 lows and 4 highs. This can be done with a matrix where the even numbered and odd numbered time slots are compared for the alternate pattern. If the ratio is different than a 5/4 ratio, either an increment or decrement of R and W is indicated.
LOCKING THE PHASE OF THE SYSTEM TO THE PULSE RATE – As described above, the packet rate is a constant for a given setup. Using the second column of the table, the rate was 4 microseconds per packet. This is many times shorter than the values of W used for the fundamental frequency of the pulse. Thus a range of packet counts can be used to change the phase of the time slots without changing the frequency. .
TS1 TS2 TS3 TS4 TS5 TS6 TS7 TS8 TS9 High Low High Low High Low High Low High Figure 4 – The condition for Odd Half Cycle Lock
To obtain a phase lock, the 9 time slot matrix above can be used. If the 5 high values are in the odd numbered time slots, this is defined as an odd half cycle lock. This will be used in the system. Thus the first step in locking the phase is to change the packet count to a point where an odd half cycle lock occurs. Since an unlocked phase would result in the beating of the pulsar pulse with the time slot clock, if displayed, the pulse would walk across the screen and appear in different time slots. To stop this walking, the count of packets is changed. Between changes, it is necessary to perform a reset of the accumulators and wait for a good S/N. Further work is needed to speed up the process of finding the lock point. This likely will involve dividing the range of counts into sub ranges and determining the rate of walking of the slots and its direction.
When the system is locked, the walking will halt. In addition, the low frequency integration in the accumulators will be operating as a coherent integrator since the phase of the system is matched to the phase of the pulsar.
DISPLAYING AND RECORDING THE PULSE PROFILE – Once the fundamental frequency and phase is locked, the display and recorded values can be increased to provide analysis of the shape of the pulse and nearby features in time. This can be done by increasing M without changing the W count.
43 However, for a wider display, it may be desirable to allow the user to create a display that shows both the fundamental and harmonics. This can be done by keeping W at integer divisor values and setting M appropriately for the display.
CONCLUSION – It appears feasible to develop a system that will meet the objective of capturing a Pulsar pulse during the time when it is present in an antenna beam width. If the antenna is capable of tracking the target pulsar, it is highly likely to be effective. If the drift scan method is used, further testing after the system coding is needed to prove the concept.
FURTHER WORK – The next step is to develop the C/C++ logic and Graphical User Interface (GUI) code necessary to carry out the process. Further knowledge will be gained from this step. Speed of processing is the primary area of concern. It likely will require a PC with multiple cores and the use of planned threads in the process. It also may be necessary to limit some of the parameters used in the system such as the frame size to accommodate the process.
Once the process is coded, it will be tested on antennas with and without tracking.
Paul Oxley is a retired AT&T Microwave Engineer.
44 Radio-Frequency Interference (RFI) From Extra-High- Voltage (EHV) Transmission Lines
Patrick C. Crane 22 March 2010
1. Introduction
The subject of radio-frequency interference (RFI) generated by high-voltage transmission lines has long been of both academic and commercial interest because of concerns about static on AM radio. Today audible noise is of greater concern because many states, counties, and municipalities have noise ordinances and transmission lines are designed to reduce audible noise, while people now expect static on AM radio (Chartier 2009). The subject is of interest today because of the proliferation around the world of low-frequency radio telescopes – including the Low Frequency Array (LOFAR), the Giant Metrewave Radio Telescope (GMRT), the Murchison Widefield Array (MWA), and the Long Wavelength Array (LWA), which is particular interest to the author.
The present discussion will concern high-voltage alternating-current (HVAC) transmission lines; high-voltage direct-current (HVDC) transmission lines will be addressed in Appendix A.
As described by Pakala and Chartier (1971) power lines are divided into two classes with respect to radio noise: (1) lines with voltages below 70 kV and (2) lines with voltages above 110 kV. Lines in the first class in general exhibit only gap-type discharges and lines in the second class principally exhibit corona discharge. Gap-type discharges are essentially a maintenance issue; corona discharges are a design issue.
Extra-high-voltage (EHV) transmission lines have operating voltages of 345 kV or greater. The possibility of interference from such a transmission line first impinged significantly upon radio astronomy (in the United States, at least) in 1984 when the El Paso Electric Company proposed building a 345-kV transmission line from Red Hill, NM to Deming, NM which would run east along US60 to its junction with NM78 (now NM52) and then south along NM78. This route would have crossed both the north and east arms about two miles from the center of the Very Large Array (VLA) radio telescope. In response, the Bureau of Land Management (BLM) hired Vernon L. Chartier of the Bonneville Power Administration (BPA) as a consultant to study the problem and recommend minimum separation distances for the VLA and for the Very Long Baseline Array (VLBA) radio telescope, construction of which began in 1985. Mr. Chartier was well qualified for the task as the Chief High Voltage Phenomena Engineer of BPA’s Division of Laboratories with many years of research in the field. He is still active and when I contacted him ([email protected]), he provided more recent references. Among them is the EPRI Red Book (2008) which is published by the Electric Power Research Institute, Inc. (EPRI); Mr. Chartier sent me the small number of relevant pages because the Red Book sells for $5000. The EPRI is an independent nonprofit
45 organization that conducts research and development relating to the generation, delivery and use of electricity for the benefit of the public. The Red Book (2008) recognizes the BPA method because
The most complete empirical method for predicting EMI above 30 MHz is the method developed by the Bonneville Power Administration (Chartier 1983). The BPA method was first developed to predict TVI from overhead lines during rain, but the method has been expanded so that EMI above 30 MHz can be calculated at any frequency, at any distance from the line, at any antenna height, for any bandwidth, and for any detector.
Furthermore, it is “the one method that is useful for EMI predictions between 30 and 1000 MHz” and “the most complete empirical method for predicting EMI above 30 MHz.”
The BPA model also has been recognized by the International Council on Large Electric Systems (CIGRE, 1996), which is one of the leading worldwide organizations on electric power systems.
2. What Is Corona?
Hubbell Power Systems, Inc. (2004) has produced a clear and concise report on corona with the title “What Is Corona?” which is available on the World Wide Web. This report defines corona in the following terms:
Corona is a luminous discharge due to ionization of the air surrounding a conductor around which exists a voltage gradient exceeding a certain critical value,
based upon IEEE Std 539-1990 (IEEE Corona and Field Effects Subcommittee, 1991) as applied to transmission-line conductors. Or in more physical terms:
The corona discharges observed at the surface of a conductor are due to the formation of electron avalanches which occur when the intensity of the electric field at the surface of a conductor exceeds a certain critical value.
Furthermore,
Any defect on the conductor[,] which projects however slightly above the nominal conductor surface, increases the field intensity in its immediate vicinity...Water drops on the conductor surface provide a multiplicity of projections from which corona discharges can originate...A weathered ACSR conductor generally has a multiplicity of tiny surface defects which project above the nominal surface of the conductor.
The presence of corona manifests itself primarily in three ways:
46 1. “Visual corona” – violet-colored light coming from the regions of electrical overstress. Daytime corona cameras and ultraviolet cameras both are used to inspect transmission lines for corona.
2. “Audible corona” – a hissing or frying sound when corona is present.
3. Radio noise – apparently this is the most serious manifestation from the point-of-view of the power company (for radio astronomers, too) because its effects have the longest range.
The phenomena associated with corona have been described quantitatively by Chartier (1983): radio noise (RI) over the frequency range 0.1-20 MHz (i.e., AM radio, ham radio); television interference (TVI) over the frequency range 10-1000 MHz, which includes VHF and UHF television and FM radio and, coincidentally, is measured in the radio-astronomy allocation 73.0-74.6 MHz because of the absence of interference; audible noise (AN); and ozone (concentration C). The total power loss per meter of conductor is identified as the corona losses (CL).
The presence of more surface defects produces higher levels of corona and related phenomena. Indulkar (2004) discusses the effects of such surface irregularities on the threshold voltage for the onset of corona. He reports that this voltage is directly proportional to an irregularity factor, m0 (0 1 for smooth, polished, solid, cylindrical conductors; 0.93-0.98 for weathered, solid, cylindrical conductors; 0.87-0.90 for weathered conductors with more than seven strands; and 0.80-0.87 for weathered conductors with up to seven strands. Finally, the Introduction states that corona from EHV transmission lines is primarily a design problem. While that is true – from the point-of-view of a radio astronomer, corona can be a maintenance issue because of such problems as degraded or damaged insulators; contamination with coastal salt, industrial vapors and dust, cement dust, road salt, tire dust and vehicle emissions; agricultural dusts and fertilizers; improper design and/or installation; and loose hardware. 3. Television Interference (TVI) As stated above the method developed by the Bonneville Power Administration (BPA) is the most complete empirical method for predicting radio-frequency interference (RFI) above 30 MHz. The BPA calculation of TVI/phase for a CISPR quasi-peak detector from corona discharge is given by Equation 9.6-4 in EPRI (2008): TVI/phase = 10 + TVIV(E) + TVIS(d) + TVIf + TVIA+ TVID(L), (1) where 47 TVI/phase = electric field (dBμV/m), measured during steady rain with an IEC/CISPRQuasi-Peak (QP) detector with a 1-ms charge time constant, a 550-ms discharge time constant, and 6-dB bandwidth of 120 kHz, for a single phase, E = conductor surface voltage gradient (kV/cm), d = subconductor diameter (cm), f = frequency (MHz), A = altitude above sea level (km), L = distance between antenna and phase (m). Individual terms will be discussed in the following sections. 3.1. Conductor Surface Voltage Gradient TVIV(E) = 120*log(E/16.3), (2) where E = conductor surface voltage gradient (kV/cm). The conductor surface voltage gradient is the single most important factor in determining the corona performance of a high-voltage transmission line. This is indicated by the multiplicative factor of 120 in front of the appropriate (second) term in Equation (1); the multiplicative factors for other terms are 40, 20, and 1. If E changes by a factor of ±2, the TVI will change by ±36 dB. It is so important, also, because its value is entirely a design issue. Therefore, the calculation of its value has long and widely been the subject of investigation. A survey of methods used for such calculations (as of 1979) was published by the IEEE Corona and Field Effects Subcommittee (1979). Seventeen techniques were applied to multiple extra-high-voltage (EHV, ≥345 kV) transmission-line configurations. Empirical techniques were found to agree with exact solutions to within a few percent, so that when applied in the field the overall uncertainty was less than ten percent. A further uncertainty may arise from the definition of the conductor surface voltage gradient; the three definitions used in the survey include the average bundle gradient (A), the average maximum bundle gradient (AM), and the maximum bundle gradient (MB). As a practical matter, Table I of the paper provides parameters for EHV transmission lines with operating voltages of 345 kV, 500 kV, 765 kV, 1100 kV, and 2000 kV (AC) and ±375 kV and ±1000 kV (DC). The computed gradients are listed in Table II. Participant No. 4 is Vernon L. Chartier and he reports only the results of an AM calculation. By 1979, such calculations had migrated to the digital computer and had expanded in capability and complexity. One can see an earlier version of the BPA calculation, suitable for manual calculation, in Pakala and Taylor (1968). I have implemented in IDL (Appendix B) the 1991 version of the Fortran code used by V. L. Chartier (Participant No. 4) for the 1979 paper and obtained exactly his results. 48 Table 1 presents the conductor surface voltage gradients reported by Participant No. 4 (IEEE Corona and Field Effects Subcommittee 1979). The numbers of phases, ground wires, and subconductors are listed to illustrate the variety of configurations included; information on horizontal and vertical offsets, diameters, and separations are in the report. It should be noted that the report presents only the two highest values of the conductor surface voltage gradients (suitable to obtain peak or quasi-peak values of static) while radio astronomers are interested in rms total power which potentially includes significant contributions from all phases and even grounds. Table 1. Conductor Surface Voltage Gradients (1979) For Participant No. 41 Line Operating Phases Ground Sub- Highest 2nd Config. Voltage Wires Conductors (kV/cm) Highest No. (kV) (kV/cm) 1 345 3 0 1 15.51 14.67 2 345 3 0 2 15.66 14.49 3a 345 6 2 2 15.50 15.20 3b 345 6 0 2 15.58 15.18 4a 500 3 2 2 16.73 16.63 4b 500 3 0 2 16.71 16.30 5 500 3 0 3 16.93 15.80 6a 765 3 2 4 21.07 19.59 6b 764 3 0 4 21.07 19.38 7 1100 3 0 8 16.55 14.98 8 2000 3 0 16 14.19 12.93 92 ±375 2 0 2 19.21 19.21 102 ±1000 2 0 8 20.47 20.47 1V.L. Chartier (BPA) 2DC The results presented in Table 1 also illustrate the effect of differences in design on the value of the conductor surface voltage gradient. Line Configuration No. 8 has an operating voltage almost three times that of Line Configuration No. 6 (2000 kV vs. 765 kV), yet its voltage gradients are about 1/3 smaller. One significant difference in design is that the subconductor bundles for Line Configuration No. 8 include sixteen subconductors instead of four. Another factor to keep in mind when evaluating the conductor surface voltage gradient is that conductor cables sag. The degree of sag depends upon the outside temperature and, especially, upon the heat generated by the electrical load. In exceptional circumstances overheated electrical cables have been known to sag so much that they touched the ground. In the case of a conductor anchored at a height H at each of two towers and which sags by an amount S at its center, the average height h is given by 49 h = H – ⅔ S. (3) This is the value that should be used to calculate the conductor surface voltage gradient. 3.2. Subconductor Diameter TVIS(d) = 40*log(d/3.04), (4) where d = subconductor diameter (cm). The subconductor diameter affects the TVI in two ways, which tend to offset each other. The first is indirectly through its effects on the values of the conductor surface voltage gradients; the larger the diameter, the lower the values. For example, Chartier (1984) reported that increasing the subconductor diameter from 1.108 inches to 1.196 would decrease the values of the conductor surface voltage gradients by 6 percent; the corresponding decrease in the value of the second term in Equation (1) would be 3.3 dB or 53 percent. The second way is directly through the third term in Equation (1). The increase in subconductor diameter mentioned in the previous paragraph would increase the TVI by 1.4 dB or 37 percent. 3.3. Frequency Dependence TVIf = 20*log(75/f), (5) where f = frequency (MHz). The data supporting this correction are discussed in Pakala and Chartier (1971). The measurements presented in their Figures 10 and 11 were obtained in fair weather at a reference distance of 200 feet (61 m) from the outer conductor of transmission lines with voltages of 244 kV, 345 kV, 525 kV, and 735 kV. In theory and practice this simple behavior breaks down at larger distances. At low frequencies of interest to the LWA and the VLA (13.385, 25.610, 37.875, 73.8, 151.525, 325.3, 408.05, and 611.0 MHz), the contributions from this term are 15, 9.3, 5.9, 0.1, -6.1, -13, -15, and -18 dB, respectively. 3.4. Altitude Dependence TVIA = (A/0.3), (6) 50 where A = altitude (km). This term reflects Paschen’s Law which states that at typical atmospheric pressures the breakdown voltage for corona discharge decreases as the pressure (density) decreases (which occurs naturally as the altitude increases). This form of the correction was derived from measurements of the radio noise (RI) produced by low-altitude (195 m) and high-altitude (3200 m) EHV transmission lines. It was later shown to describe the behavior of television interference (TVI) by Chartier et al. (1987). This term is relatively unimportant, since a change in altitude from sea level to 3 km results in an adjustment of only 10 dB. 3.5. Lateral Attenuation TVID(L) = 20*log(L0/L), for L and L0 ≤ Lc, (7a) = 20*log(L0/Lc) + 40*log(Lc/L), for L ≥ Lc and L0 ≤ Lc, (7b) = 20*log(Lc/L) + 40*log(L0/Lc), for L ≤ Lc and L0 ≥ Lc, (7c) = 40*log(L0/L), for L and L0 ≥ Lc, (7d) where ha = antenna height (m), H = conductor height (m), λ = wavelength (m), L = lateral distance between phase and antenna (m), L0 = 61 m (200 ft), reference lateral distance, -1 Lc = 12 ha H λ , changeover distance. This relatively simple expression accounts for the lateral attenuation of TVI in the BPA method for corona discharge from EHV transmission lines. Nominally, it applies to frequencies between 30 MHz and ≥1000 MHz; at distances of interest to us it probably applies to frequencies ≥10 MHz (Chartier 2009). This expression does not depend explicitly upon frequency but an implicit dependence is introduced by the changeover distance, Lc, which marks the boundary between near-field and far-field behavior. At frequencies of interest to the LWA (13.385, 25.610, 37.875, and 73.8 MHz), the values of the changeover distance are 16.7 m, 32.0 m, 47.4 m, and 92.3 m, respectively. The lateral attenuation is normalized to unity (0 dB) at L0 independent of frequency and the transition from near-field to far-field behavior (L-2 to -4 L ) occurs at Lc. Consequently, at lower frequencies for which L ≥ L0 ≥ Lc and at the large distances of interest to us, we have 51 TVID(L) = 40*log(L0/L), (8a) which is frequency independent. On the other hand, at higher frequencies for which L ≥ Lc ≥ L0 and at the same large distances, we have TVID(L) = 20*log(L0/Lc) + 40*log(Lc/L), (8b) which is systematically greater than the prior result (since Lc ≥ L0) and frequency- dependent through the presence of Lc. These behaviors are illustrated in Figure 1. However, if the distances are normalized to the value of Lc at 75 MHz: 6 -1 L75 = 12*10 ha H f c , (9) the sum of Equations (5) and (8b) can be simplified to TVIf + TVID(L) = 20*log(L0/L75) + 40*log(L75/L), L ≥ Lc ≥ L0. (10) Surprisingly, as long as L ≥ Lc ≥ L0, the TVI/phase is independent of frequency, which is apparent in Figures 2, 3, and 4. The propagation of radio waves over a finitely conducting plane was first addressed by Sommerfeld (1909). These results were simplified for engineering work (Norton 1936, 1937) and extended eventually to the case of the finitely conducting spherical Earth (Norton 1941). Additional simplifications are provided by Pakala and Chartier (1971). I have not determined the provenance of Equation (4) but it is accepted by the domestic (EPRI 2008) and international (CIGRE 2000) electric power industries. Equation (4) applies to distances between approximately 61 m and 15000 m. At shorter distances interference between the space wave (itself a combination of direct and ground- reflected waves), the surface wave, the induction field, and the electrostatic field predominates – all propagating over a finitely conducting earth. At larger distances the curvature of the earth is important as is the variation of atmospheric refraction with altitude. 4. Detector, Bandwidth, and Power Equation (1) is based upon a CISPR quasi-peak (QP) detector with a bandwidth of 120 kHz. However, in practice, a different detector and different bandwidth may be used; the following conversion procedure originated with Chartier (1988). Corrections to other detectors and bandwidths are given in Tables 2 and 3, respectively, which are based upon Table 9.6-1 and Equations 9.6-5, 9.6-6, and 9.6-7 in the EPRI Red Book (2008). 52 TVI/phase in Equation (1) is an electric field whereas radio astronomers measure noise power. The steps in making the conversion from TVI (dBμV/m) to noise power P(dBW/m2/Hz) are (1) Convert from dBμV to dBV Correction = -120 dB. (11) (2) Convert from quasi-peak electric field to rms electric field Correction = -10 dB. (12) (3) Convert from a bandwidth of 120 kHz to a bandwidth of 1 Hz Correction = 10*log(1/120000) dB = -50.8 dB. (13) (4) Convert from rms electric field to noise power, which is done via P = E2/Z, (14) where P = noise power (W/m2/Hz), E = rms noise voltage (V/m/Hz1/2), Z = impedance of free space (377 Ω). Or 10*log[P(W/m2/Hz)] = 20*log[E(V/m/Hz1/2)] – 10*log(377), (15) P(dBW/m2/Hz) = E(dBV/m/Hz1/2) - 25.8 dB. (16) Finally, P(dBW/m2/Hz) = TVI(dBμV/m) – 206.6 dB. (17) Table 2. Corrections from QP to Other Detectors Detector Correction Quasi-Peak +0 dB Peak +5 dB RMS -10 dB Table 3. Bandwidth Corrections 1 Detector Correction (ΔEpk) Quasi-Peak +0 dB Peak 20 log (BW/BW0) dB 53 RMS 10 log (BW/BW0) dB Average 10 log (BW/BW0) dB 1 BW0 = 120 kHz 5. Operating Voltages Extra-high-voltage (EHV) transmission lines are labeled by voltages of 345 kV, 500 kV, 765 kV, 1100 kV, and even 2000 kV. But these voltages are only nominal. The actual operating voltages may be significantly higher; they are set by the individual utilities and will vary during the day as the nature of the load changes. There are, however, standards for the maximum voltages which manufacturers use to design and build the high-voltage equipment. The maximum extra-high voltages as established by the American National Standards Institute (ANSI C84.1-2006) are listed in Table 4; I found them listed in the IEEE Dictionary (IEEE 100). Table 4. Operating Voltages for EHV Transmission Lines1 Nominal (kV) Actual (kV)2 Maximum (kV) 345 ~350 362 500 ~535 550 765 … 800 1100 … 1200 1ANSI C84.1-2006 2Bonneville Power Administration It should be noted that operating voltages are rms phase-to-phase while the voltages used to calculate voltage gradients are rms line-to-ground; the latter are thus a factor of 31/2 smaller than the former. 6. Weather The altitude dependence discussed above is a simple example of the effects of the environment on TVI. More generally, weather has significant, but highly variable, effects. For example, according to Chartier (2009), a typical plot of an all-weather RI distribution is the superposition of three distinct Gaussian distributions: (1) high values during mean rainy weather (i.e., conductors thoroughly wet), (2) low values during mean fair weather, and (3) a transition distribution between measurable rain and fair weather - i.e., when the conductors are wet with dew, fog, light snow, and after rain - or in the presence of pollution caused by industry, farmers plowing their fields, etc. The BPA method calculates the TVI level during mean rainy weather but in very heavy rain the TVI level may be even higher (Pakala and Chartier 1971; Chartier 2009). Table 5. Adjustment for Weather Conditions Weather Condition Adjustment Heavy Rain +5 dB 54 Mean Rainy Weather 0 dB Mean Fair Weather -25 dB 7. Thresholds for Harmful Interference In the United States, electromagnetic interference from power transmission systems is governed by the Federal Communications Commission (FCC) Rules and Regulations presently in existence (FCC, 1988). A power transmission system falls into the FCC category of “incidental radiation device,” which is defined as “a device that radiates radio frequency energy during the course of its operation although the device is not intentionally designed to generate radio frequency energy.” Such a device “shall be operated so that the radio frequency energy that is emitted does not cause harmful interference. In the event that harmful interference is caused, the operator of the device shall promptly take steps to eliminate the harmful interference.” For purposes of these regulations, harmful interference is defined as: “any emission, radiation or induction which endangers the functioning of a radio navigation service or of other safety services or seriously degrades, obstructs or repeated interrupts a radio communication service operating in accordance with this chapter” [FCC 1988]. This statement is reproduced from the Final Environmental Impact Statement for the Klondike III/Biglow Canyon Wind Integration Project (BPA 2006). The frequency range (10-88 MHz) of the LWA includes five allocations for radio astronomy; six other allocations are (or eventually may be) of interest to the VLA (Table 6). Table 6. Low-Frequency Allocations for Radio Astronomy Frequency Range Description (U.S.) 13360-13410 kHz Primary 25550-25670 kHz Primary 37.5-38.0 MHz Secondary, Land Mobile Primary 38.0-38.25 MHz Primary, Shared with Fixed and Mobile 73.0-74.6 MHz Primary 150.05-153.0 MHz Fixed, Mobile, and Land Mobile Primary* 322.0-328.6 MHz Footnote, Fixed and Mobile Primary* 406.1-410.0 MHz Primary, Shared with Fixed and Mobile 608.0-614.0 MHz Primary, Shared with Land Mobile 1400.0-1427.0 MHz Primary, Shared with Earth-Exploration Satellite (passive) and Space Research (passive) *Radio Astronomy Primary Outside U.S. Twenty-five years ago it was recognized that synthesis-imaging arrays were intrinsically less sensitive to radio-frequency interference (RFI) than single radio telescopes that operate in total-power mode. In the case of a connected-element array fringe-frequency averaging and broadband decorrelation (Thompson 1982) may reduce the sensitivity to RFI significantly [see Figure 15.2 in Thompson, Moran, and Swenson (2001)]. In the 55 case of the VLA, in particular, these effects reduce its sensitivity to RFI by 15 dB, 19 dB, and 22 dB at 73.8 MHz, 325 MHz, and 1413.5 MHz, respectively (Crane 1985). However, what may be overlooked is that radio-astronomical arrays – such as the LWA – today and in the future need not be used exclusively for synthesis imaging. Indeed, one need only look at the science proposed for the first station of the LWA (LWA-1) to understand how erroneous that view is – pulsar spectra, “giant” pulses, scintillation and scattering effects; all-sky monitoring for transient events; low-frequency radio recombination lines; ionospheric-transparency events; ionospheric scintillation; frequency structure of solar and Jovian radio bursts; interplanetary scintillation. And, because multiple, independently tuned and pointed beams will be provided, both interferometric and total-power observations likely will occur simultaneously. Consequently, the appropriate protection criteria for the LWA are those recommended by the International Telecommunications Union (ITU) for a radio telescope operating in total-power mode in “ITU-R Recommendation RA.769-2: Protection Criteria for Radioastronomical Measurements” (ITU 2003): The harmful interference level is that level of interference which equals 0.1 of the rms noise level which sets the fundamental limit of the data. The corresponding spectral power flux density, ΔSH (Wm-2Hz-1), is given by 2 -1/2 2 -1 ΔSH = 0.4πf kTS(Bt) (c Gs) , (18) where f is the observing frequency; k, Boltzman’s constant; TS, the system temperature; B, the observing bandwidth; c, the speed of light; Gs, the gain, with respect to an isotropic antenna (λ2/4π), of the antenna in the direction of the arrival of the interfering signal; and t, the total integration time. RA.769-2 adopts a total integration time of 2000 seconds, which is intermediate between short observations of time-varying phenomena and deep spectral-line observations. An antenna gain Gs of 0 dBi is adopted as a compromise between the high gain of the main beam and the low gain of the distant sidelobes. The system temperature, TS, is the sum of the antenna noise temperature, TA, and the receiver noise temperature, TR, or TS = TA + TR. (19) The Galactic background dominates the antenna temperatures at low frequencies; RA.769-2 uses the minimum temperatures observed at the North Galactic Pole in its calculations. The minimum temperature for 37.875 MHz was provided by Emil Polisensky (2009) using his program LFmap (Polisensky 2007). Table 7. Threshold Levels of Harmful Interference (RA.769-2) Center Frequency Assumed Minimum Antenna Receiver Noise Spectral pfd fc Bandwidth Noise Temperature Temperature ΔSH -2 -1 (MHz) Δf TA TR (dB(Wm Hz )) (MHz) (K) (K) 13.385 0.05 50000 60 -248 25.610 0.12 15000 60 -249 37.875 0.75 4000* 60 -255 56 73.8 1.6 750 60 -258 151.525 2.95 150 60 -259 325.3 6.6 40 60 -258 408.05 3.9 25 60 -255 611.0 6.0 20 60 -253 1413.5 27.0 12 10 -255 *Polisensky (2009) The thresholds of harmful interference derived in RA.769-2 are summarized in Table 7. ΔSH is fairly constant between 13.385 MHz and 1413.5 MHz but at higher frequencies 2 the f dependence dominates and ΔSH decreases rapidly. 8. Minimum Separation Distances As described in Section 5, there are several standard (nominal) operating voltages for EHV transmission lines: 345 kV, 500 kV, 765 kV, and 1100 kV. The El Paso Electric transmission line is 345 kV. The High Plains Express and SunZia projects are planning for 500-kV transmission lines, possibly even double-circuit 500-kV transmission lines. 765-kV transmission lines are not uncommon in the United States and the line configuration (No. 6) analyzed by the IEEE Corona and Field Effects Subcommittee (1979) has the highest conductor surface voltage gradients of those analyzed, so using it will provide a conservative estimate for the minimum separation distances. The values of the voltage gradients, however, need to be scaled to the maximum operating voltage of 800 kV. Since we have converted from quasi-peak electric field to rms electric field to noise power, it is necessary to sum the contributions from the three phases. A final conservative assumption is that conditions of heavy rain apply. The various assumptions that will form the basis for the calculations of minimum separation distances are listed in Table 8. The distances will be calculated for the LWA and the VLA; Table 8 includes appropriate heights for the LWA and VLA antennas and altitudes for the continental divide at Pie Town (a possible LWA site) and the VLA site on the Plains of San Augustin. Table 8. Assumptions for Calculation of Minimum Separation Distances Line Configuration No. 6 Three phases No ground wires Conductor surface voltage gradients 21.07 kV/cm (Center Phase) and 19.38 kV/cm (Outer Phase) for operating voltage of 765 kV Scale from 765 kV to operating voltages of 800 kV and 510 kV Antenna heights of 1.5 m (LWA) and 25 m (VLA) Altitudes of 7796 ft (LWA) and 7000 ft (VLA) Heavy rain (+5 dB) Total noise power => Sum contributions from three phases Total-power observations 57 Threshold levels of harmful interference from Table 7 The minimum separation distances (Figure 2 and Table 9) derived for a transmission line with an operating voltage of 800 kV and the LWA are exactly compatible with the separation distance of 10 miles (16.09 km) that has been discussed with the New Mexico Renewable Energy Transmission Authority (NMRETA). However, given that the conductor surface voltage gradient is more fundamental than the operating voltage, it is more appropriate to say: For a single circuit, as long as the conductor surface voltage gradients are less than about 22 kV/cm, 10 miles or more is a sufficient separation distance from the LWA. On the other hand, the derived minimum separation distances at the six radio-astronomy allocations of interest to the VLA are considerably greater than 10 miles (Figure 3 and Table 9). The reason is that the changeover distances for the transition from near-field to far-field behavior are much greater than for the LWA because of the greater height of the antenna and the shorter wavelengths. Decreasing the operating voltage to 510 kV, however, provides minimum separation distances that are exactly compatible with a separation distance of 10 miles (Figure 4 and Table 9). Therefore, subject to the caveat about operating voltages and conductor surface voltage gradients and for a single circuit, as long as the conductor surface voltage gradients are less than about 14 kV/cm, 10 miles or more is a sufficient separation distance from the VLA. Table 9. Minimum Separation Distances Center Frequency Distance Distance1 Distance2 fc (LWA) (VLA) (VLA) (MHz) (km) (km) (km) 13.385 16.15 … … 25.610 12.37 … … 37.875 14.37 … … 73.8 15.05 58.64 15.19 151.525 … 64.12 16.09 325.3 … 58.64 15.19 408.05 … 48.34 12.78 611.0 … 43.97 10.19 1413.5 … 49.34 5.55 1800 kV: 22.03 kV/cm (C.P.) and 20.27 kV/cm (O.P) 2510 kV: 14.05 kV/cm (C.P.) and 12.92 kV/cm (O.P) It is important to remember that the values of the conductor surface voltage gradients are essentially a design feature of a transmission line. The values are largely determined by the operating voltage and by the design of the subconductor bundle. Using subconductors with larger radii and bundles including more subconductors both reduce the value of the voltage gradient. On the other hand, as discussed in Section 3.2, the term TVIS(d) increases as the subconductor diameter increases, offsetting in part the effect of decreasing the voltage gradient. 58 The preparation of this report is very timely because on 29 May 2009 the Bureau of Land Management announced that it was initiating the process to prepare the Environmental Impact Statement for the SunZia Southwest Transmission Project which is proposed to run from Bingham, NM (near Socorro) to Tucson, AZ by way of San Antonio, NM and Deming, NM. The proposed and alternate routes pass near several possible LWA sites: SA, CU, EN, HN, AK, and NM. The proposed line configuration includes two 500-kV transmission lines. Consequently, the noise power from six phases (and grounds, potentially) must be summed, and possibly a larger minimum separation distance will be necessary. For us to evaluate a proposal for EHV transmission line, we shall require the complete set of physical parameters for the transmission line(s): maximum operating voltages; horizontal and vertical offsets; numbers, diameters, and separations of subconductors; numbers and diameters of grounds; conductor sag; number and separation of circuits; and altitudes. This information will allow us to evaluate the potential for radio-frequency interference using the BPA method (USDOE/Bonneville Power Administration, undated). 9. Acknowledgements I wish to thank Vernon L. Chartier for his invaluable assistance in the preparation of this memorandum. Basic research in radio astronomy at the Naval Research Laboratory is supported by the Office of Naval Research. 10. References Accredited Standards Committee on Preferred Voltage Ratings for AC Systems and Equipment, C84, 2006, ANSI C84.1-2006: American National Standard for Electric Power Systems and Equipment – Voltage Ratings (60 Hertz), National Electrical Manufacturers Association, Roslyn, Virginia. BPA, 2006, Final Environmental Statement: Klondike III/Biglow Canyon Wind Integration Project, Appendix C: Electrical Effects, Bonneville Power Administration, Portland, Oregon (http://www.efw.bpa.gov/environmental_services/Document_Library/Klondike/Appendi xC.pdf/). Chartier, V. L., 1983, “Empirical Expressions for Calculating High Voltage Transmission Corona Phenomena,” Proceedings of First annual Seminar, Technical Career Program for Professional Engineers, April 1983, pp. 75-82. Chartier, V. L., 1984, “Evaluation of Electromagnetic Interference from El Paso Electric Red Hill to Deming 345-kV Line on the Very Large Array Radio Telescope,” Bonneville Power Administration, Laboratory Report ER-84-18. 59 Chartier, V. L., 1988, "Comprehensive Empirical Formulas for Predicting EMI from Overhead Power Line Corona," Proceedings of the 1988 U.S.-Japan Seminar on Electromagnetic Interferences in Highly Advanced Social Systems (Modeling, Characterization, Evaluation and Protection), August 1-4, 1988, Honolulu, Hawaii, pp. 5- 1 to 5-11. Chartier, V. L., 2009, private communication. Chartier, V. L., Lee, L. Y., Dickson, L. D., and Martin, K. E., 1987, “Effect of High Altitude on High Voltage AC Transmission Line Corona Phenomena,” IEEE Transactions on Power Delivery 2 (1), 225-236. CIGRE, 1996, Addendum to CIGRE Document No, 20 (1974), Interferences Produced by Corona Effect of Electric Systems – Description of Phenomena and Practical Guide for Calculation, International Council on Large Electric Systems, Paris, France. Crane, P. C., 1985, “The Responses of the Very Large Array and the Very Long Baseline Array to Interfering Signals,” VLA Scientific Memorandum No, 156. EPRI, 2008, EPRI AC Transmission Line Reference Book – 200 kV and Above, Third Edition, Electric Power Research Institute, Palo Alto, California. FCC, 1988, Federal Communications Rules and Regulations, 10-1-88 Edition, Volume II, Part 15, 47 CFR, Chapter 1, Federal Communications Commission, Washington, D.C. Hubbell Power Systems, Inc., 2004, What Is Corona?, Bulletin EU1234-H, Hubbell Power Systems, Inc., Centralia, Missouri (http://www.hubbellpowersystems.com/powertest/literature_library/pdfs4lib/OB/EU1234 -H.pdf). IEEE Corona and Field Effects Subcommittee, 1979, “A Survey of Methods for Calculating Transmission Line Conductor surface Voltage Gradients,” IEEE Transactions on Power Apparatus and Systems PAS-98 (6), 1996-2014. IEEE Corona and Field Effects Subcommittee, 1991, IEEE Std 539-1990: IEEE Standard Definitions of Terms Relating to Corona and Field Effects of Overhead Power Lines, The Institute of Electrical and Electronics Engineers, Inc., New York, New York. IEEE Standards Project Editors, 2000, The Authoritative Dictionary of IEEE Standards Terms (IEEE 100), Seventh Edition, IEEE Standards Information Network (SIN)/IEEE Press, Piscataway, New Jersey, p. 1261. 60 Indulkar, C. S., 2004, “Sensitivity Analysis of Corona and Radio Noise in EHV Transmission Lines,” Journal IE(I)-EL 84(4), 197-200. ITU, 2003, “ITU-R Recommendation RA.769-2: Protection Criteria for Radioastronomical Measurements,” ITU-R Recommndations, RA Series, International Telecommunications Union, Geneva. Morris, R. M., and Maruvada, P. S., 1976, “Conductor Surface Voltage Gradients on Bipolar HV dc Transmission Lines,” IEEE Transactions on Power Apparatus and Systems PAS-95 (6), 1934-1945. Norton, K. A., 1936, “Propagation of Radio Waves Over the Surface of the Earth and in the Upper Atmosphere, Part I,” Proc. IRE 24, 1367-1387. Norton, K. A., 1937, “Propagation of Radio Waves Over the Surface of the Earth and in the Upper Atmosphere, Part II,” Proc. IRE 25, 1203-1236. Norton, K. A., 1941, “The Calculation of Ground-Wave Field Intensity Over a Finitely Conducting Spherical Earth,” Proc. IRE 29, 623-639. Olsen, R. G., Schennum, S. D., and Chartier, V. L., 1992, “Comparison of Several Methods for Calculating Power Line Electromagnetic Interference Levels and Calibration with Long Term Data,” IEEE Transactions on Power Delivery 7 (2), 903-913. Pakala, W. E., and Chartier, V. L., 1971, “Radio Noise Measurements on Overhead Power Lines from 2.4 to 800 kV,” IEEE Transactions on Power Apparatus and Systems PAS-90 (3), 1155-1165. Pakala, W. E., and Taylor, E. R., 1968, “A Method for Analysis of Radio Noise on High- Voltage Transmission Lines,” IEEE Transactions on Power Apparatus and Systems PAS-87 (2), 334-345. Polisensky, E., 2007, “LFmap: A Low Frequency Sky Map Generating Program,” Long Wavelength Array (LWA) Memorandum No. 111. Polisensky, E., 2009, private communication. Sommerfeld, A., 1909, “The Propagation of Waves in Wireless Telegraphy,” Ann. Phys. 28, 665-736. Thompson, A. R., 1982, “The Response of a Radio-Astronomy Synthesis Array to Interfering Signals,” IEEE Transactions on Antennas and Propagation AP-30, 450-456. Thompson, A. R., Moran, J. M., and Swenson, G. W., 2001, Interferometry and Synthesis in Radio Astronomy, Second Edition, Wiley-Interscience, New York. 61 USDOE, Bonneville Power Administration, undated, “Corona and Field Effects” Computer Program (Public Domain Software), Bonneville Power Administration, Post Office Box 491-ELE, Vancouver, WA 98666. 62 Appendix A. High-Voltage Direct-Current (HVDC) Transmission Lines High-voltage direct-current (HVDC) transmission lines are not common in the United States. But 500-kV transmission lines of this type are under consideration for the SunZia Southwest Transmission Project. The following discussion is included for the sake of completeness. According to CIGRE (1996), Positive pulsative corona is the dominant source of [RFI] on direct-current (DC) transmission lines because the current pulses induced by corona discharges on the positive conductor have much higher amplitudes than those on the negative polarity conductor…Experimental studies have shown that DC lines produce very little [RFI] above 30 MHz. …contrary to the case of AC lines, the RI [radio interference] level of a bipolar DC line decreases in rain or wet snow. The BPA calculation for RI/(positive phase) for a CISPR quasi-peak detector from corona discharge from a high-voltage direct-current (HVDC) transmission line is given by Equation 7.4 of CIGRE (1996), for frequencies f ≤ 30 MHz: RI/(positive phase) = 51.7 + RIV(E) + RIS(d) + RIf +RIA +RID(L), (A.1) where RI/(positive phase) = electric field (dBμV/m), measured during mean fair weather, with 550-ms discharge time constant, and 6-dB bandwidth of 120 kHz, for a single phase, E = conductor surface voltage gradient (kV/cm), d = subconductor diameter (cm), f = frequency (MHz), A = altitude above sea level (km), L = distance between antenna and positive phase (m). However, by adjusting the constants inside the logarithmic terms, it is possible to rewrite Equation (A.1) in terms familiar from the discussion of TVI in Section 3: RI/(positive phase) = 8.1 + 0.717*TVIV(E) + TVIS(d) + RIf + TVIA + RID(L). (A.2) Superficially this resembles Equation (1) for TVI from EHV transmission lines, including the value of the initial constant. A.1. Conductor Surface Voltage Gradient 63 The factor of 0.717 (86/120) multiplying TVIV(E) indicates that the dependence on the conductor surface voltage gradient of RI from HVDC transmission lines is weaker than that of TVI from EHV transmission lines. For example, doubling the values of the conductor surface voltage gradient increases the contributions to RI and TVI by factors of 25.8 dB and 36 dB, respectively. On the other hand, for the largest values in Table 1 of conductor surface voltage gradient for HVDC and EHV transmission lines, the contributions of these terms to RI and TVI, 8.5 dB and 13.4 dB, respectively, differ by only a few dB. A.2. Frequency Dependence 2 RIf = 10*[1 - log (10*f)], (A.3) where f = frequency (MHz). At low frequencies of interest to the LWA (13.385 and 25.610 MHz), the contributions from this term are -35 and -48.0 dB, respectively, which correspond to the values of 15 and 9.3 dB calculated for TVI. The large numerical differences arise because the reference frequency for RI is 0.5 MHz or 1.0 MHz and that for TVI is 75 MHz. RIf is zero at 0.1 MHz and TVIf is zero at 75 MHz. A.3. Lateral Attenuation RID(L) = 40*log(L0/L), (A.4) where L = lateral distance between positive phase and antenna (m) L0 = 61 m (200 ft), reference lateral distance This is the same result as the far-field limit of TVID(L) given in Equation (8a). A.4. Detector, Bandwidth and Power Equations (A.1) and (A.2) are based upon a CISPR quasi-peak (QP) detector with a bandwidth of 120 kHz. As discussed above in Section 4, in practice, a different detector and different bandwidth may be used. The conversion from electric field to noise power is the same: P(dBW/m2/Hz) = RI(dBμV/m) - 206.6 dB. (A.5) A.5. Weather 64 As noted in Section 6, Equation (1) calculates the TVI level during conditions during mean rainy weather. To adjust the result to the same conditions of mean fair weather that apply to Equations (A.1) and (A.2), the result for TVI must be adjusted downward by -25 dB (Table 5). A.6. Summary As noted above, Equations (1) and (A.2) superficially resemble each other, including the values of the numerical constant. But the introductory comments suggest that the RI and TVI generated by HVDC transmission lines are significantly less than those generated by EHV transmission lines. The primary difference in value between the calculations of RI from HVDC transmission lines and TVI from EHV transmission lines is introduced by the frequency corrections. For frequencies of interest to the LWA below 30 MHz, on average the difference between Equation (5) and Equation (A.3) is about -50 dB. This is only partially compensated by the 25-dB adjustment of Equation (1) to mean fair weather. The contribution of the conductor surface voltage gradient is perhaps 5 db smaller for RI from HVDC transmission lines. Overall it appears that RI from HVDC transmission lines is about 30 dB less than TVI from EHV transmission lines at frequencies below 30 MHz; it is realistic to assume that a similar factor applies to TVI at higher frequencies from HVDC transmission lines relative to that from EHV transmission lines. 65 Appendix B. IDL Subroutines for Conductor Surface Voltage Gradient Calculation of conductor surface voltage gradients is the only quantity or effect discussed in this report not amenable to simple and straightforward calculation. Instead I obtained the FORTRAN files CSMXGRAD.TXT, CSMXINVR.TXT, and C3INCL.TXT from the “Corona and Field Effects” Computer Program (USDOE/Bonneville Power Administration, undated) from Vernon L. Chartier. They were combined and translated into a single IDL (Interactive Data Language) subroutine, BPA_CSVG.PRO, for the calculation of conductor surface voltage gradients. An IDL procedure, TEST_BPA_CSVG.PRO, was written and used to test BPA_CSVG.PRO on the thirteen different conductor configurations studied by the IEEE Corona and Field Effects Subcommittee (1979). The results of these tests` agreed exactly with those of Participant No. 4, who was Vernon L. Chartier. The two IDL routines are listed below. pro bpa_csvg,numph,numgnd,xdist,ydist,numsubcond,diam,subspc,volts, $ phase,acdc,gradcomp ; ; IDL procedure to calculate conductor surface voltage gradients for an ; array of energized conductors and ground wires ; ; inputs ; ; numph = number of energized phases ; numgnd = number of ground wires ; xdist = (numph+numgnd) array of horizontal distances from reference ; (m) ; ydist = (numph+numgnd) array of vertical distances from ground (m) ; numsubcond = (numph+numgnd) array of numbers of subconductors in ; bundles ; diam = (numph+numgnd) array of diameters of single subconductor (cm) ; subspc = (numph+numgnd) array of subconductor spacings (cm) ; volts = (numph+numgnd) array of operating voltages kV ; phase = (numph+numgnd) array of phase angles (degrees) ; acdc = (numph+numgnd) array of ac/dc flags (0 for ground, 1 for AC, 2 ; for DC) ; ; notes ; ; the operating voltages for AC transmission lines are phase-to-phase ; rms voltages ; the voltages used to calculate conductor surface voltage gradients ; are line-to-ground rms voltages ; therefore V(line-to-ground)=V(phase-to-phase)/sqrt(3) for AC ; ; no conversion is necessary for DC ; ; outputs ; ; gradcomp = (numph+numgnd) array of computed conductor surface voltage ; gradients (kV/cm) ; qreal = (numph+numgnd) array of computed real components of ; charge(Coulomb?) ; qimag = (numph+numgnd) array of computed imaginary components of ; charge (Coulomb?) 66 ; ; BACKGROUND ; ; Conductor gradient calculation routine for CORONA and field effects ; program ; ; author ; ; U. S. Department of Energy - Bonneville Power Administration ; Paul Kingery ; ; purpose ; ; To calculate the surface gradient for each conductor. Also, ; calculate the real and imaginary charge factors ; for each conductor. ; ; history ; ; Originally written by Douglas Lewis, 15 December 1984. ; Modified by Paul Kingery to use C3INCL.FOR include file, June 1991, ; as well as extensive modifications abnd ; code cleanup. ; ; Converted to IDL function by Patrick Crane, June 2009 ; ; constants ; zero=0.0d0 tenth=0.1d0 one=1.0d0 two=2.0d0 three=3.0d0 root2=sqrt(two) root3=sqrt(three) four=4.0d0 ten=10.0d0 fifty=50.0d0 hundred=100.0d0 one80=180.0d0 thousand=1000.0d0 pi=3.1415926536d0 halfpi=pi/two twopi=two*pi rootpi=sqrt(pi) root2pi=root2*rootpi d2r=pi/one80 r2d=one80/pi eps1=18.0d9 eps2=18.0d6 n360x10=3600 ; ; initialize variables ; numcond=numph+numgnd ; total number of energized and ground conductors pmatrix=dblarr(numcond,numcond) ; square matrix qtotal=zero ; total charge 67 radius=dblarr(numcond) ; bundle radius spacing=dblarr(numcond) ; effective bundle spacing vreal=dblarr(numcond) ; real voltage vimag=dblarr(numcond) ; imaginary voltage bundiam=dblarr(numcond) ; effective bundle diameter deq=dblarr(numcond) ; equivalent diameter ; ; output arrays ; gradcomp=dblarr(numcond) ; computed conductor gradient qreal=dblarr(numcond) ; computed real component of charge qimag=dblarr(numcond) ; computed imaginary component of charge ; ; intermediate results in calculation of gradients ; ck2=zero frb=zero ; ; do conversions ; ; convert phase-to-phase voltages to line-toground voltages for AC ; ACDCF=1 => all AC ; wac=where((acdc eq 1),nac) if (nac gt 0) then begin volts(wac)=volts(wac)/root3 acdcf=1 endif ; ; check for AC-DC mix ; ACDCF=2 => all DC ; ACDCF=0 => mix ; wdc=where((acdc eq 2),ndc) if (ndc gt 0) then acdcf=2 if (nac*ndc gt 0) then acdcf=0 ; ; calculate radii and set defaults for numsubcond=1 ; radius=diam/two spacing=radius bundiam=diam ; ; loop for each conductor to compute effective radius and diameter ; for i=0,numcond-1 do begin rnsc=double(numsubcond[i]) if (numsubcond[i] gt 1) then begin spacing[i]=subspc[i] bundiam[i]=subspc[i]/sin(pi/rnsc) endif deq[i]=(bundiam[i]*(rnsc*diam[i]/bundiam[i])^(one/rnsc))/hundred endfor ; ; loop for each conductor and compute square matrix ; 68 for i=0,numcond-1 do begin for j=0,numcond-1 do begin ; ; do calculation as if diagonal element ; pmatrix[i,j]=eps1*alog(ydist[j]*four/deq[i]) ; ; redo calculation for non-diagonal elements ; if (i ne j) then $ pmatrix[i,j]=eps1*alog(sqrt((xdist[i]-xdist[j])^two+ $ (ydist[i]+ydist[j])^two)/ $ sqrt((xdist[i]-xdist[j])^two+ $ (ydist[i]-ydist[j])^two)) endfor endfor ; ; invert the square matrix with IDL function LA_INVERT which uses LU ; decomposition and LAPACK routines ; pmatrix=la_invert(pmatrix) ; ; loop around circle in tenths of a degree ; for i=0,n360x10-1 do begin ; ; loop for each conductor ; for j=0, numcond-1 do begin if ((i ne 0) and (acdc[j] eq 1)) then phase[j]=phase[j]+tenth ; ; compute real and imaginary voltages ; vreal[j]=volts[j]*cos(phase[j]*d2r)*thousand vimag[j]=volts[j]*sin(phase[j]*d2r)*thousand endfor ; ; perform matrix multiplications ; qreal=pmatrix##vreal qimag=pmatrix##vimag ; ; loop for each conductor and compute gradient ; for j=0,numcond-1 do begin rnsc=double(numsubcond[j]) qtotal=sqrt(qreal[j]^two+qimag[j]^two) ck2=two*(rnsc-one)*sin(pi/rnsc) frb=qtotal*(one+ck2/(spacing[j]/radius[j]))*eps2/(rnsc*radius[j]) if (i eq 0) then gradcomp[j]=frb if (frb gt gradcomp[j]) then gradcomp[j]=frb endfor ; ; do not continue main loop if all AC or DC ; if (acdcf ne 0) then break endfor 69 ; ; loop for each conductor to adjust sign of gradient ; for i=0,numcond-1 do if (volts[i] lt zero) then $ gradcomp[i]=-gradcomp[i] ; ; return with calculated gradients ; return end *********************************************************************** ; test_bpa_csvg.pro ; ; IDL procedure to test bpa_csvg function for calculating conductor ; surface voltage gradients ; using BPA model and subroutine ; ; calls IDL procedure ; bpa_csvg,numph,numgnd,xdist,ydist,numsubcond,diam,subspc,volts, $ ; phase,acdc,gradcomp ; ; inputs ; ; numph = number of energized phases ; numgnd = number of ground wires ; xdist = (numph+numgnd) array of horizontal distances from reference ; (m) ; ydist = (numph+numgnd) array of vertical distances from ground (m) ; numsubcond = (numph+numgnd) array of numbers of subconductors in ; bundles ; diam = (numph+numgnd) array of diameters of single subconductor (cm) ; subspc = (numph+numgnd) array of subconductor spacings (cm) ; volts = (numph+numgnd) array of operating voltages kV (phase-to-phase ; rms for AC) ; phase = (numph+numgnd) array of phase angles (degrees) ; acdc = (numph+numgnd) array of ac/dc flags (0 for ground, 1 for AC, ; 2 for DC) ; ; outputs ; ; gradcomp = (numph+numgnd) array of computed conductor surface voltage ; gradients ; qreal = (numph+numgnd) array of computed real components of charge – ; N/A ; qimag = (numph+numgnd) array of computed imaginary components of ; charge - N/A ; ; line configuration no. 1 from the IEEE Corona and Field Effects ; Subcommittee Report (1979) ; numph=3 numgnd=0 xdist=[-7.92d0,0.0d0,7.92d0] ydist=11.18d0*[1,1,1] numsubcond=[1,1,1] 70 diam=4.475d0*[1,1,1] subspc=0.0d0*[1,1,1] volts=345.0d0*[1,1,1] phase=[-120.0d0,0.0d0,120.0d0] acdc=[1,1,1] bpa_csvg,numph,numgnd,xdist,ydist,numsubcond,diam,subspc,volts,phase, $ acdc,gradcomp print,'line configuration no. 1',gradcomp ; ; line configuration no. 2 from the IEEE Corona and Field Effects ; Subcommittee Report (1979) ; numph=3 numgnd=0 xdist=[-8.31d0,0.0d0,8.31d0] ydist=13.61d0*[1,1,1] numsubcond=2*[1,1,1] diam=3.08d0*[1,1,1] subspc=45.72d0*[1,1,1] volts=345.0d0*[1,1,1] phase=[-120.0d0,0.0d0,120.0d0] acdc=[1,1,1] bpa_csvg,numph,numgnd,xdist,ydist,numsubcond,diam,subspc,volts,phase, $ acdc,gradcomp print,'line configuration no. 2',gradcomp ; ; line configuration no. 3a from the IEEE Corona and Field Effects ; Subcommittee Report (1979) ; numph=6 numgnd=2 xdist=[6.12d0*[-1,1],8.405d0*[-1,1],6.425d0*[-1,1],3.66d0*[-1,1]] ydist=[26.31d0*[1,1],18.85d0*[1,1],12.29d0*[1,1],33.93d0*[1,1]] numsubcond=[2*[1,1,1,1,1,1],1,1] diam=[3.165d0*[1,1,1,1,1,1],1.463d0*[1,1]] subspc=[45.72d0*[1,1,1,1,1,1],0.0d0*[1,1]] volts=[345.0d0*[1,1,1,1,1,1],0.0d0*[1,1]] phase=[120.0d0*[-1,1],0.0d0*[1,1],120.0d0*[1,-1],0.0d0*[1,1]] acdc=[1,1,1,1,1,1,0,0] bpa_csvg,numph,numgnd,xdist,ydist,numsubcond,diam,subspc,volts,phase, $ acdc,gradcomp print,'line configuration no. 3a',gradcomp ; ; line configuration no. 3b from the IEEE Corona and Field Effects ; Subcommittee Report (1979) ; numph=6 numgnd=0 xdist=[6.12d0*[-1,1],8.405d0*[-1,1],6.425d0*[-1,1]] ydist=[26.31d0*[1,1],18.85d0*[1,1],12.29d0*[1,1]] numsubcond=2*[1,1,1,1,1,1] diam=3.165d0*[1,1,1,1,1,1] subspc=45.72d0*[1,1,1,1,1,1] volts=345.0d0*[1,1,1,1,1,1] phase=[120.0d0*[-1,1],0.0d0*[1,1],120.0d0*[1,-1]] acdc=[1,1,1,1,1,1] bpa_csvg,numph,numgnd,xdist,ydist,numsubcond,diam,subspc,volts,phase, $ 71 acdc,gradcomp print,'line configuration no. 3b',gradcomp ; ; line configuration no. 4a from the IEEE Corona and Field Effects ; Subcommittee Report (1979) ; numph=3 numgnd=2 xdist=[-6.095d0,0.0d0,6.095d0,-3.935d0,3.935d0] ydist=[13.94d0,22.32d0,13.94d0,33.29d0,33.29d0] numsubcond=[2,2,2,1,1] diam=[4.069d0,4.069d0,4.069d0,0.978d0,0.978d0] subspc=[45.72d0,45.72d0,45.72d0,0.0d0,0.0d0] volts=[500.0d0,500.0d0,500.0d0,0.0d0,0.0d0] phase=[-120.0d0,0.0d0,120.0d0,0.0d0,0.0d0] acdc=[1,1,1,0,0] bpa_csvg,numph,numgnd,xdist,ydist,numsubcond,diam,subspc,volts,phase, $ acdc,gradcomp print,'line configuration no. 4a',gradcomp ; ; line configuration no. 4b from the IEEE Corona and Field Effects ; Subcommittee Report (1979) ; numph=3 numgnd=0 xdist=[-6.095d0,0.0d0,6.095d0] ydist=[13.94d0,22.32d0,13.94d0,33.29d0,33.29d0] numsubcond=[2,2,2] diam=[4.069d0,4.069d0,4.069d0] subspc=[45.72d0,45.72d0,45.72d0] volts=[500.0d0,500.0d0,500.0d0] phase=[-120.0d0,0.0d0,120.0d0] acdc=[1,1,1] bpa_csvg,numph,numgnd,xdist,ydist,numsubcond,diam,subspc,volts,phase, $ acdc,gradcomp print,'line configuration no. 4b',gradcomp ; ; line configuration no. 5 from the IEEE Corona and Field Effects ; Subcommittee Report (1979) ; numph=3 numgnd=0 xdist=[-12.19d0,0.0d0,12.19d0] ydist=14.43d0*[1,1,1] numsubcond=3*[1,1,1] diam=2.959d0*[1,1,1] subspc=45.72d0*[1,1,1] volts=500.0d0*[1,1,1] phase=[-120.0d0,0.0d0,120.0d0] acdc=[1,1,1] bpa_csvg,numph,numgnd,xdist,ydist,numsubcond,diam,subspc,volts,phase, $ acdc,gradcomp print,'line configuration no. 5',gradcomp ; ; line configuration no. 6a from the IEEE Corona and Field Effects ; Subcommittee Report (1979) ; 72 numph=3 numgnd=2 xdist=[-13.72d0,0.0d0,13.72d0,-10.975d0,10.975d0] ydist=[20.83d0,20.83d0,20.83d0,31.49d0,31.49d0] numsubcond=[4,4,4,1,1] diam=[2.959d0,2.959d0,2.959d0,0.978d0,0.978d0] subspc=[45.72d0,45.72d0,45.72d0,0.0d0,0.0d0] volts=[765.0d0,765.0d0,765.0d0,0.0d0,0.0d0] phase=[-120.0d0,0.0d0,120.0d0,0.0d0,0.0d0] acdc=[1,1,1,0,0] bpa_csvg,numph,numgnd,xdist,ydist,numsubcond,diam,subspc,volts,phase, $ acdc,gradcomp print,'line configuration no. 6a',gradcomp ; ; line configuration no. 6b from the IEEE Corona and Field Effects ; Subcommittee Report (1979) ; numph=3 numgnd=0 xdist=[-13.72d0,0.0d0,13.72d0] ydist=[20.83d0,20.83d0,20.83d0] numsubcond=[4,4,4] diam=[2.959d0,2.959d0,2.959d0] subspc=[45.72d0,45.72d0,45.72d0] volts=[765.0d0,765.0d0,765.0d0] phase=[-120.0d0,0.0d0,120.0d0] acdc=[1,1,1] bpa_csvg,numph,numgnd,xdist,ydist,numsubcond,diam,subspc,volts,phase, $ acdc,gradcomp print,'line configuration no. 6b',gradcomp ; ; line configuration no. 7 from the IEEE Corona and Field Effects ; Subcommittee Report (1979) ; numph=3 numgnd=0 xdist=[-15.24d0,0.0d0,15.24d0] ydist=21.34d0*[1,1,1] numsubcond=8*[1,1,1] diam=3.556d0*[1,1,1] subspc=45.72d0*[1,1,1] volts=1100.0d0*[1,1,1] phase=[-120.0d0,0.0d0,120.0d0] acdc=[1,1,1] bpa_csvg,numph,numgnd,xdist,ydist,numsubcond,diam,subspc,volts,phase, $ acdc,gradcomp print,'line configuration no. 7',gradcomp ; ; line configuration no. 8 from the IEEE Corona and Field Effects ; Subcommittee Report (1979) ; numph=3 numgnd=0 xdist=[-35.00d0,0.0d0,35.00d0] ydist=45.00d0*[1,1,1] numsubcond=16*[1,1,1] diam=3.810d0*[1,1,1] 73 subspc=45.72d0*[1,1,1] volts=2000.0d0*[1,1,1] phase=[-120.0d0,0.0d0,120.0d0] acdc=[1,1,1] bpa_csvg,numph,numgnd,xdist,ydist,numsubcond,diam,subspc,volts,phase, $ acdc,gradcomp print,'line configuration no. 8',gradcomp ; ; line configuration no. 9 from the IEEE Corona and Field Effects ; Subcommittee Report (1979) ; numph=2 numgnd=0 xdist=[-6.095d0,6.095d0] ydist=13.92d0*[1,1] numsubcond=[2,2] diam=4.577d0*[1,1] subspc=45.72d0*[1,1] volts=375.0d0*[-1,1] phase=[0.0d0,0.0d0] acdc=[2,2] bpa_csvg,numph,numgnd,xdist,ydist,numsubcond,diam,subspc,volts,phase, $ acdc,gradcomp print,'line configuration no. 9',gradcomp ; ; line configuration no. 10 from the IEEE Corona and Field Effects ; Subcommittee Report (1979) ; numph=2 numgnd=0 xdist=8.38d0*[-1,1] ydist=18.29d0*[1,1] numsubcond=[8,8] diam=4.572d0*[1,1] subspc=45.72d0*[1,1] volts=1000.0d0*[-1,1] phase=[0.0d0,0.0d0] acdc=[2,2] bpa_csvg,numph,numgnd,xdist,ydist,numsubcond,diam,subspc,volts,phase, $ acdc,gradcomp print,'line configuration no. 10',gradcomp stop end 74 75 76 77 78 Callisto‐Pi: Callisto Spectrograms from Raspberry Pi Abbreviations: Whitham D. Reeve FITS: Flexible Image Transport System FTP: File Transfer Protocol LAN: Local Area Network 1. Introduction PNG: Portable Network Graphics RPi: Raspberry Pi This paper describes how to use the inexpensive Raspberry Pi computer to WAN: Wide Area Network automatically produce spectrogram images in near real‐time from Callisto WLAN: Wireless LAN FITS data files (figure 1). In this article the hardware is called RPi and the hardware together with software is called Callisto‐Pi. The RPi is used rather than a Windows desktop PC because the installation and operation on a Windows PC of the many Python libraries and dependencies needed for Callisto‐Pi would require huge effort and time and have a low probability of success. All libraries were originally written for the Linux operating system and run naturally on the RPi whose operating system is based on Linux. My involvement in developing this application was merely as project manager. Others did all the hard work (see Acknowledgements at the end). As a service to Callisto users I have made available an RPi hardware platform with a preprogrammed 8 GB memory card setup to run Callisto‐Pi (see Contact Information at the end). Real‐ time spectrograms produced by Callisto‐Pi may be viewed at {Reeve} and {Nelson}.The Callisto‐Pi project is a follow‐up to my LWA TV Raspberry Pi project Note: Internet links in braces { } described at [RvLWATV]. and references in brackets [ ] are provided in section 7. Figure 1 ~ Image of the first Callisto spectrogram produced by Callisto‐Pi from a FITS file over a 15 minute interval starting at 1945. It shows a Type II radio burst on 16 April 2014 at 1957; the horizontal bands are radio frequency interference, mostly from TV broadcast stations. The vertical axis is frequency and horizontal axis is time. Color indicates intensity relative to the background noise level. See text for additional details. (Image © 2014 W. Reeve) The standard file format for data produced by the e‐Callisto solar radio spectrometer network is the NASA‐ designed Flexible Image Transport System {FITS}. Archived and current data and spectrogram images for all Callistos that participate in the network are available online at {CallistoData}. These data and images generally 79 are accessible within 30 to 120 minutes after the FITS files are produced at a given Callisto station. However, there often is a need to prepare spectrograms in near real‐time for local viewing or for posting on a user’s website. Callisto‐Pi meets this need at low complexity and cost. A Callisto spectrogram simultaneously shows three pieces of related information – frequency, time and received intensity. Frequency is shown on the vertical axis in MHz with the low frequency limit at the top. Callisto‐Pi automatically scales the spectrogram frequency scale between 10 and 870 MHz according to the frequency data in the FITS file. Time is shown in Coordinated Universal Time (UTC) on the horizontal axis in HH:mm:ss, progressing left to right. Most Callisto spectrograms cover a 15 min interval starting at HH:00:00, HH:15:00, HH:30:00 and HH:45:00 throughout local daylight hours. Intensity is a relative scale indicated by colors. Darker colors (blue) indicate lower intensities and lighter colors (green, yellow, orange, through red) indicate progressively higher intensities. The scale is logarithmic (nonlinear in absolute power) so the color indicates the relative power in dB of each frequency‐time pixel. 2. Raspberry Pi and Callisto‐Pi Hardware: The Raspberry Pi is a low‐cost, small computer platform designed for educational purposes by the Raspberry Pi Foundation {RPi}. The RPi can be plugged into an ordinary computer monitor or TV and can use a wired Ethernet connection or WiFi wireless access device for LAN and internet access and a wired USB or Bluetooth wireless keyboard and mouse. However, the RPi used in Callisto‐Pi is operated “headless” in which no monitor, keyboard or mouse is required for setup or operation. Callisto‐Pi requires an internet connection if spectrogram images are to be sent to and viewed on an internet website. Figure 2 ~ Raspberry Pi model B and B+ hardware. The model B+ is shown in an aluminum enclosure with USB WLAN and BlueTooth dongles (left) and with no enclosure (middle). The model B (right) also is in an aluminum enclosure. The interfaces vary slightly between the model B and B+ but Callisto‐Pi works on both models. Enclosure dimensions are approximately 100 x 65 x 25 mm. (Image © 2014 W. Reeve) The RPi hardware has become available in three versions – original model A (not generally available in North America), model B and model B+. Callisto‐Pi has been tested only with the model B and B+ (figure 2), and there is no advantage of one over the other. The RPi uses an SD memory card (B) or micro‐SD memory card (B+) for program storage. Refer to [Reeve] or online search for a more detailed hardware description. Software: Callisto‐Pi uses a software image on the memory card that includes the operating system and Python software applications, libraries and support files. The operating system is based on a Raspbian distribution. Callisto‐Pi uses relatively simple scripts to call Python libraries and routines. The bulk of the work is done by 80 three libraries: SunPy {SunPy}, which processes the FITS files; MatPlotLib {MatPlotLib}, which plots the spectrograms as PNG image files; and Optipng {Optipng}, which optimizes (reduces) the size of the image file for web use. 3. Basic Operation The system block diagram shows how the various components work together (figure 3). An ordinary Windows PC controls the CALLISTO instrument. It typically produces a FITS file at 900 s (15 min) intervals as determined by the Callisto configuration file. Minimum Equipment List: • Raspberry Pi B or B+ Callisto • Power supply PC • 8 GB memory card CALLISTO Optional Internet WLAN Callisto‐Pi using Router Ethernet Local Area Raspberry Pi Internet Network Model B or B+ 5 V Power USB Network AC Power Flash Attached Adapter or HD Storage Figure 3 ~ System block diagram. Callisto‐Pi collects FITS files from the Callisto PC, processes them and then sends the spectrogram images to a website and archive storage. (Image © 2014 W. Reeve) The Callisto PC is configured to send each new FITS file to Callisto‐Pi, which acts as an adjunct spectrogram processor to produce an image file. After producing the image file, Callisto‐Pi sends it to a website (or any FTP server) for viewing. These images are produced as picture.png files and are disposable; that is, each new image overwrites the previous image. Callisto‐Pi also sends a date‐ and time‐stamped copy of the image (based on the original FITS date and time) to local Network Attached Storage (NAS) or, alternately, to a USB flash or hard drive connected to the RPi. Two program functions embedded in the Raspbian distribution called crontab and launcher.sh control Callisto‐Pi actions. Crontab loads and runs when Callisto‐Pi is powered up and whenever it is rebooted. Crontab then loads launcher, a shell (command line interpreter) with a list of actions and routines that produce and send the images. Underlying these activities are FTP server and client functions that load automatically and operate in the background. 4. Spectrogram Production The scripts used to run Callisto‐Pi are relatively simple because the SunPy and MatPlotLib libraries do all the complicated work “under the hood”. The user needs to tell the Callisto PC where to send the FITS files and to tell Callisto‐Pi where to send the processed images (figure 4). A CallistoSpectrogram function in the SunPy library is called to calculate the background noise level for each new FITS file and then to subtract that level before the spectrogram is produced. Thus, the displayed intensities are relative to the calculated background. The 81 displayed intensities follow a standard color map for solar imaging originally developed for the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) spacecraft mission. Figure 4 ~ Callisto‐Pi flowchart. A launcher script collects data and controls production of the spectrogram images and then sends the images to a web server and archive storage. (Image © 2014 W. Reeve) When there is considerable radio frequency interference in the data, the background calculation can limit the displayed intensity range and weak solar radio bursts or other natural phenomena in the data may be masked by the noise. However, each file is calculated separately. Therefore, the background calculation has no memory beyond the current spectrogram and there are no lingering effects beyond the 15 min data interval. 5. Installation and Operation Callisto‐Pi uses stock RPi hardware with no modifications. The software image is contained on an 8 GB memory card. As mentioned earlier, a display, keyboard and mouse are not required. All setup can be performed from a Windows PC running a Secure Shell (SSH) terminal program such as PuTTY or Tera Term. Complete step‐by‐step instructions are included with the Callisto‐Pi Package. Before use, the launcher script in Callisto‐Pi needs to be setup for the user’s specific environment. This is done with a built‐in editor in Callisto‐Pi. Also, external devices need to be setup to send files to and receive files from Callisto‐Pi. In summary, it is necessary to • Setup the Windows PC running Callisto software to send FITS files to Callisto‐Pi • Edit the launcher for the user’s specific Callisto‐Pi environment including LAN and WAN addresses and login details. • Setup the external webserver to receive and display Portable Network Graphics (PNG) images from Callisto‐Pi (this typically is an internet web server) • Setup a local NAS or USB‐drive for archive storage of PNG files 82 6. Conclusions Callisto‐Pi is a small, inexpensive, maintenance‐free platform that produces near real‐time spectrogram images from Callisto FITS files. It has applications with any CALLISTO instrument where a user wishes to produce their own images for posting and display on a website. No programming is required. A built‐in editor is used to configure the Callisto‐Pi for the user’s specific environment, including LAN and web server addresses and archive storage. 7. References and Web Links [RvLWATV] Reeve, W., LWA TV on the Raspberry Pi, Society of Amateur Radio Astronomers, Radio Astronomy, September‐October 2014 {CallistoData} http://soleil.i4ds.ch/solarradio/callistoQuicklooks/ {FITS} http://fits.gsfc.nasa.gov/fits_home.html {MatPlotLib} http://matplotlib.org/ {Optipng} http://optipng.sourceforge.net/ {Python} https://www.python.org/ {Reeve} http://www.reeve.com/e‐CALLISTO/Callisto_Spectrogram/CallistoSpectro_simple.html {Nelson} http://www.roswellmeteor.com/e‐Callisto2/picture.png {RPi} http://www.raspberrypi.org/ {SunPy} http://sunpy.org/ Acknowledgements: I am grateful to two people in particular for their help developing Callisto‐Pi: Phil Costigan and my son Whitham Reeve II. Phil is a member of Astronomical Society of Victoria – Radio Astronomy Section (ASV‐RAS). He wrote the Python code that produces the Callisto spectrograms for the Leon Mow Radio Observatory (http://lmro.org.au/) and provided the script to me. My son is a Linux expert, and he adapted the code to Callisto‐Pi and developed the launcher shell routines. In addition, the automatic production of spectrograms from Callisto FITS files would have been quite difficult without the SunPy and MatPlotLib libraries. These libraries required the work of many people. In addition, the SunPy and MatPlotLib libraries depend on other code and libraries produced by many others in the Python user community {Python}. Ordering Callisto‐Pi: A Calllisto‐Pi Package may be ordered by sending an email inquiry to the address right; be sure to put something meaningful in the email Subject line or else the email will be automatically deleted by the server. The Callisto‐Pi Package includes the RPi model B+ in an aluminum enclosure, preprogrammed 8 GB memory card and 10 W power supply with interchangeable worldwide ac input plugs. The preprogrammed memory card also is available without the RPi hardware. The memory card is supplied as a micro‐SD memory card in a full‐size SD card carrier (adapter), so it will work in either the model B or B+. Instructions for the necessary user setup are provided with the Callisto‐Pi Package. Prices: Callisto‐Pi Package: 143 USD plus postage Callisto‐Pi memory card: 20 USD plus postage. 83 SETI League executive director H. Paul Shuch, who has served on the SARA board and as Vice‐President, with the GBT...SETI League photo http://www.setileague.org/ 84 FIRST LIGHT of TLM‐18 Antenna System The TIROS Restoration Team would like to announce first light at 21cm for the TLM‐18 antenna system. First light occurred on 19 January, 2015 at approximately 17:00 GMT. The TLM‐18 is a 60 foot prime focus parabolic antenna located in Wall Township, New Jersey, USA. It was first used to support the TIROS I and TIROS II weather satellites and subsequently, the MINITRACK program. It was decommissioned in the mid 1970s and later de‐militarized by the US Army prior to transfer of the property to InfoAge via Wall Township, New Jersey. The TIROS Restoration Team is composed of volunteers from the Information Age Learning Center (InfoAge), The Ocean‐Monmouth Amateur Radio Club (OMARC), and Princeton University. Signal peak riding on top of the noise background at 0.4 MHz (actually TLM‐18 Antenna with 21cm feed Post processed drift plot 1420.4 MHz), which is the in place at 45 degree elevation well‐known 21 cm radiation from the Milky Way. Higher resolution images are available upon request, all rights reserved. Media Contact: Dan Marlow, K2QM at [email protected] Martin A Flynn / W2RWJ Ocean-Monmouth Amateur Radio Club, Inc 2300 Marconi Road Wall Township, NJ 07719 Tel: +01 732-428-7373 Email: [email protected] Visit us online at: www.n2mo.org 85 Book Review Title: Radio Propagation ~ Principles and Practice Author: I. Poole Publisher: Radio Society of Great Britain (RSGB) ISBN:978‐1872‐309972 Date published: 2004 Length: 102 pages, 2 page index Status: In print Availability: Paperbound from ARRL for US$30 or RSGB for £9.99 (about US$17) (see text) Reviewer: Whitham D. Reeve Radio propagation is an important subject for radio astronomers and radio operators, among others. Radio Propagation ~ Principles and Practice was written from the perspective of high frequency terrestrial communications as are almost all amateur radio books on this subject. Someone new to radio astronomy could usethis book to learn the fundamentals of radio propagation from the bottom up. They could then move to more advanced books or professionally written online materials that discuss propagation through the ionosphere from the top down. As printed on the back cover, the author is “an electronics and engineering consultant and journalist at Adrio Communications”. He also publishes the Radio Electronics website at http://www.radio‐electronics.com/, “Resources and analysis for electronics engineers”, which is a source of numerous highly simplified electronics tutorials. His writing style is British English (not unexpectedly). Radio Propagation ~ Principles and Practice has 10 chapters: Electromagnetic waves; The atmosphere; The Sun; Propagation near the ground; Ionospheric propagation; Ionospheric disturbances, storms and auroras; Predicting, assessing and using ionospheric propagation; Tropospheric propagation; Meteor scatter; and Space communications. The chapters are compact, fairly well‐illustrated and easy to read but readers should not expect a lot of depth. Even though the processes that form the ionosphere are very complex, and even today are not completely understood, this book shows that it is possible to skirt the math and provide relatively simple explanations. I spotted only a few simple equations. The book starts out by describing electromagnetic waves, the atmosphere (and ionosphere) and the Sun. These set the stage for discussions of the various types of high frequency propagation discussed later. I noted some discussions that were either too simplified or only partially correct. For example, in chapter 3 – The Sun, the author first states that the Sun rotates faster at its equator and low latitudes than high latitudes and then on the next page says the Sun’s equator rotates slower (the former is correct). The next two chapters cover ground wave and sky wave propagation and include a little history on how the ionosphere was discovered (readers wanting more historical detail should see Probing the Sky with Radio Waves ~ From Wireless Technology to the Development of Atmospheric Science by Chen‐Pang Yeang, which I will review in the near future). Chapter 4 – Ionospheric Propagation describes refraction and reflection of radio waves in Earth’s upper atmosphere, which is ionized by the Sun’s radiation. Refraction, or bending, through the ionized medium at altitudes of a few hundred kilometers allows radio waves to travel far beyond the visible horizon. However, the ionosphere is quite variable throughout the day and changes drastically at night, which 86 affects the maximum and minimum usable frequencies for any given path. The author’s discussions of the Maximum Usable Frequency (MUF) and Lowest Usable Frequency (LUF) could have been better written. A reader unfamiliar with these terms, in other words, the target audience for this book, might find the discussion confusing. Many radio astronomers are interested in detecting meteor trail reflections, the subject of chapter 9 – Meteor scatter. When a meteor encounters the resistance of Earth’s atmosphere, heat from friction ionizes the thin air and the molecules in the meteor body and leaves an ionized trail that refracts or reflects terrestrial radio waves. The electron density in these trails can exceed the density of the normal ionosphere. The trails usually last only a short time before they dissipate, but they may be used for terrestrial communications (meteor communications), which is the focus of this chapter. I was a little disappointed in the last chapter on Space Communications. While the primary purpose of the book is terrestrial radio propagation, as a radio astronomer I am interested in reception of radio waves from celestial sources through Earth’s ionosphere, the equivalent of receiving from a spacecraft or satellite. I was hoping for more details than provided in this chapter. Faraday rotation and scintillation are very briefly discussed in terms of Earth‐Moon‐Earth (EME) communications (but too briefly to be of any use). This chapter yielded little else besides what seemed to be a focus on satellite orbits. Of course, in a small book like this, there is little opportunity to provide very many technical details, but I still think it should have been more to the point. I found some passages repetitious, but the discussions are adequate for purposes of amateur radio. The book provides many rules of thumb that could provide a stepping stone for further study. Unfortunately, like almost all books written for the radio amateur market, there are no references or even a list of books for further study. This is a serious impediment to someone wanting to learn more and makes this book easily disposable. This small book may be purchased directly from RSGB. The American Radio Relay League (ARRL) also sells the book but their price is far too high. Interestingly, when I started writing this review (June 2014), used copies were selling for a shocking US$300. The book is not a so‐called classic and that price is off by a factor of at least 30. More recently (January 2015) I have seen used prices from 14 to US$35, still too high for a used book of this type. In conclusion, Radio Propagation ~ Principles and Practice provides an adequate introduction but it lacks depth. Although the book has little direct applicability to radio astronomy, it would help a newcomer to amateur radio astronomy to understand some of the characteristics of high frequency propagation and contribute to their overall knowledge. The inconsistencies that I mentioned along with several editing mistakes are minor flaws. However, at US$30 plus shipping, the book is overpriced for US buyers unless they order directly from RSGB at a lower price or are able to find an inexpensive used copy. Reviewer ‐ Whitham Reeve presently is a contributing editor for the SARA journal, Radio Astronomy. He worked as an engineer and engineering firm owner/operator in the airline and telecommunications industries for more than 40 years and has lived in Anchorage, Alaska his entire life. 87 Membership New Members Please welcome our new or returning SARA members who have joined since the last journal. If your name is missing or misspelled, please send an email to treasurer@radio‐astronomy.org. We will make sure it appears correctly in the next Journal issue. As of February 26, 2015: First Name Last Name City State Country Ham ID Walter “Sandy” Bettilyon Villa Rica GA USA KK4PZS Myron China Centennial CO USA KB0LMQ John Chmielewski Franklin NC USA N2XD Patrick Davis Orlando FL USA KY3I Larry Dodd Jasper GA USA Geof Franklin Maysville GA USA KE4IGD Devoyon Guillaume Canejan Gironde France F8ARR Justine Haupt Rocky Point NY USA W2GFO Carl Herbert Inverness FL USA AA2JZ Robert Hoffmaster Port Hadlock WA USA KE6YMJ Eve Klopf Klamath Falls OR USA AD5FP Michael T McEwen Medicine Park OK USA K5OSA Michael Miciukiewicz Trumbull CT USA K1MJM Andrew Stern Eugene OR USA N7UL William Wachspress Lawrence KS USA William West Wellington CO USA W0WST Christopher Wilkin Okoboji IA USA SARA Membership Dues and Promotions Membership dues are $20.00 US per year and all dues expire in June. Student memberships are $5.00 US per year. Members joining from June to December of 2014 will renew their membership June 2015. Members joining January to June 2015 will renew June 2016. Or pay once and never worry about missing your dues again with the SARA Life Membership. SARA Life Memberships are now offered for a one‐time payment of twenty times the basic annual membership fee (currently $400 US). Journal Archives & Other CDs Promotion The entire set of The Journal of The Society of Amateur Radio Astronomers is available on CD. It goes from the beginning of 1981 to the end of 2014 (over 5000 Tor of SARA history!) Or you can choose one of the following CD’s or DVD:* (Prices are US dollars and include postage.) SARA Journals from 1981 through 2014 SARA Mentor CD, compiled by Jim Brown SARA Navigator (IBT) CD and DVD, compiled by Jon Wallace Prices, US dollars, including postage 88 Members Each disk $15.00 Disk + 1 year membership extension $30.00 Non‐members Each disk $25.00 Disk + 1 year membership $30.00 Non‐USA members Each disk $20.00 (airmail) Disk + 1 year members extension $35.00 *Already a member and want any or all of these CD’s or DVD’s? Buy any one for $15.00 or get any three for $35.00. SARA Store(http://www.radio‐astronomy.org/e‐store) SARA offers the above CDs, DVDs, printed Proceedings and Proceedings on CD and other items at the SARA Store: http://www.radio‐astronomy.org/e‐store. Proceeds from sales go to support the student grant program. Members receive an additional 10% discount on orders over $50 US. Payments can be made by sending payment by PayPal to treasurer@radio‐astornomy.org or by mailing a check or money order to SARA, c/o Melinda Lord, 2189 Redwood Ave, Washington, IA 52353 SARA Online Discussion Group SARA members participate in the online forum at http://groups.google.com/group/sara‐list. This is an invaluable resource for any amateur radio astronomer. SARA Conferences SARA organizes multiple conferences each year. Participants give talks, share ideas, attend seminars, and get hands‐on experience. For more information, visit http://www.radio‐astronomy.org/meetings. Facebook Like SARA on Facebookhttp://www.facebook.com/pages/Society‐of‐Amateur‐Radio‐ Astronomers/128085007262843 Twitter Follow SARA on Twitter #radio astronomy1 What is Radio Astronomy? This link is for a booklet explaining the basics of radio astronomy. http://www.radio‐astronomy.org/pdf/sara‐beginner‐booklet.pdf 89 Administrative Officers, directors, and additional SARA contacts The Society of Amateur Radio Astronomers is an all‐volunteer organization. The best way to reach people on this page is by email with SARA in the subject line SARA Officers President: Ken Redcap, president@radio‐astronomy.org, +1 248‐630‐6810 Vice President: Tom Hagen, vicepres@radio‐astronomy.org, +1 248‐650‐8951 Secretary: Bruce Randall, secretary@radio‐astronomy.org, +1 803‐327‐3325 Treasurer: Melinda Lord, treasurer@radio‐astronomy.org, +1 319‐591‐1130 Past President: William Lord, tbd@radio‐astronomy.org, +1 319‐591‐1131 Founder Emeritus & Director: Jeffrey M. Lichtman, [email protected], +1 954‐554‐3739 Board of Directors Name Term expires Email Jim Brown 2015 [email protected] Chip Sufitchi 2015 [email protected] Carl Lyster 2016 [email protected] Stephen Tzikas 2016 [email protected] David James 2016 [email protected] Curt Kinghorn 2015 [email protected] Keith Payea 2016 [email protected] Stan Nelson 2015 [email protected] Other SARA Contacts All Officers ‐‐‐‐ officers@radio‐astronomy.org Annual Meeting Coordinator Vice President vicepres@radio‐astronomy.org All Radio Astronomy Editors ‐‐‐ editor@radio‐astronomy.org Radio Astronomy Editor Kathryn Hagen [email protected] Radio Astronomy Contributing Editor Christian Monstein [email protected] Radio Astronomy Contributing Editor Whitham D. Reeve [email protected] Radio Astronomy Contributing Editor Stan Nelson [email protected] Educational Outreach Jon Wallace education@radio‐astronomy.org Grant Committee ‐‐‐‐ grants@radio‐astronomy.org International Ambassador Librarian Membership Chair Tom Crowley membership@radio‐astronomy.org Mentor Program Jon Wallace mentor@radio‐astronomy.org Navigators Tom Crowley [email protected] Technical Queries David Westman technical@radio‐astronomy.org Webmaster Ciprian (Chip) Sufitchi webmaster@radio‐astronomy.org 90 Resources Great Projects to Get Started in Radio Astronomy Radio Observing Program The Astronomical League (AL) is starting a radio astronomy observing program. If you observe one category, you get a Bronze certificate. Silver pin is two categories with one being personally built. Gold pin level is at least four categories. (Silver and Gold level require AL membership which many clubs have membership. For the bronze level, you need not be a member of AL.) Categories include 1) SID 2) Sun (aka IBT) 3) Jupiter (aka Radio Jove) 4) Meteor back‐scatter 5) Galactic radio sources This program is collaboration between NRAO and AL. William F Bogardus is the Lead Coordinator and a SARA member. For more information: http://www.astroleague.org/programs/radio‐astronomy‐observing‐program The Radio Jove Project monitors the storms of Jupiter, solar activity and the galactic background. The radio telescope can be purchased as a kit or you can order it assembled. They have a terrific user group you can join. http://radiojove.gsfc.nasa.gov/ 91 The INSPIRE program uses build‐it‐yourself radio telescope kits to measure and record VLF emissions such as tweeks, whistlers, sferics, and chorus along with man‐made emissions. This is a very portable unit that can be easily transported to remote sites for observations. http://theinspireproject.org/default.asp?contentID=27 Sky Scan Awareness Project When a meteor passes through the Earth's atmosphere, it ionizes the atmosphere which improves its ability to reflect radio waves. This allows you to briefly hear a far away radio station that you normally couldn't detect. In this project, you can install an antenna, use an FM radio receiver, computer software, and learn to observe meteor showers using this very simple radio telescope. For more information about this project, please visit http://www.skyscan.ca/getting_started.htm . SARA/Stanford SuperSID Stanford Solar Center and the Society of Amateur Radio Astronomers have teamed up to produce and distribute the SuperSID (Sudden Ionospheric Disturbance) monitor. The monitor utilizes a simple pre‐amp to magnify the VLF radio signals which are then fed into a high definition sound card. This design allows the user to monitor and record multiple frequencies simultaneously. The unit uses a compact 1 meter loop antenna that can be used indoors or outside. This is an ideal project for the radio astronomer that has limited space. To request a unit, send an e‐mail to supersid_at_radio‐astronomy_dot_org At Right‐ Mr Potato Head checks out the Itty Bitty Telescope (IBT) Photo courtesy Mark Gibson. More information on making your own IBT go to http://www.gb.nrao.edu/epo/ibt.shtml 92 Education Links Free online Introductory Astronomy course: http://www.davidiadevaia.com/ASTRO/index1.html American Geophysical Union Launches Free Science News Website ~ Eos, Newspaper of the Earth and Space Sciences: https://eos.org/ STAFF is a dynamic online timeline viewer that allows you to plot and compare solar data. The data includes x‐ray, sunspots, radio measurements, proton and electron flux near Earth, solar wind and interplanetary magnetic field parameters, geomagnetic and ionospheric data, and readings from EUV solar images. You can increase the number of data points if you want higher time resolution. You can zoom in or you can let the program choose the optimal sample interval for your desired timespan: http://www.staff.oma.be/ Exact Solution to Model Big Bang, Quark Gluon Plasma Published: http://www.scientificcomputing.com/news/2014/12/exact‐solution‐model‐big‐bang‐quark‐gluon‐ plasma‐published?et_cid=4335411&et_rid=210447177&location=top Compilation of memorable solar events in 2014 (put on your seatbelt): https://www.youtube.com/watch?v=dnTMtpNvlyc Eos, Earth & Space Science News – Magnetic Storms and Induction Hazards ~ Electric fields induced in the Earth’s lithosphere during magnetic storms can interfere with the operation of electric power grids: https://eos.org/features/magnetic‐storms‐induction‐hazards Everyone loves a conspiracy especially one involving the US government and Earth’s magnetic field ~ Guilty Knowledge: What the US Government Knows about the Vulnerability of the Electric Grid, But Refuses to Fix: http://www.centerforsecuritypolicy.org/2014/03/12/guilty‐knowledge/ And here’s another one: Comet Conspiracy! Here's Why We Haven't Seen Color Photos of 67P: http://motherboard.vice.com/en_uk/read/comet‐conspiracy‐heres‐why‐we‐havent‐seen‐colour‐photos‐ of‐67p?trk_source=recommended Any landing you can walk away from is a good one ~ Rosetta's Comet Lander Will Revive After Bumpy Touchdown, Scientists Say: http://news.nationalgeographic.com/news/2014/12/141217‐rosetta‐philae‐ comet‐wake‐science‐space/ Rosetta Reignites Debate on Earth's Oceans (or, We have one data point, so let us now extrapolate the daylights out of it): http://science.nasa.gov/science‐news/science‐at‐nasa/2014/14dec_cometwater/ STEREO Science Center, Search for STEREO images: http://stereo‐ ssc.nascom.nasa.gov/cgi‐bin/images Probing Jovian Decametric Emission with the Long Wavelength Array Station 1 (Submitted 23 Dec 2014): http://arxiv.org/abs/1412.7237 93 Physics Today ~ A geometrically determined distance to a far‐off black hole: http://scitation.aip.org/content/aip/magazine/physicstoday/news/10.1063/PT.5.7130?utm_medium=e mail&utm_source=Physics+Today&utm_campaign=5111820_Physics+Today%3a+The+week+in+Physics+ 8‐12+December&dm_i=1Y69,31KB0,HPI212,AXR6J,1 Physics Today ~ Emphasis on short‐term gains worries Australia’s science community: http://scitation.aip.org/content/aip/magazine/physicstoday/article/67/12/10.1063/PT.3.2615?utm_me dium=email&utm_source=Physics+Today&utm_campaign=5111820_Physics+Today%3a+The+week+in+ Physics+8‐12+December&dm_i=1Y69,31KB0,HPI212,AXR6J,1 Physics Today ~ The Deep Space Network at 50: http://scitation.aip.org/content/aip/magazine/physicstoday/article/67/12/10.1063/PT.3.2619?utm_me dium=email&utm_source=Physics+Today&utm_campaign=5143729_Physics+Today%3a+The+week+in+ Physics+15‐19+December&dm_i=1Y69,328XD,HPI212,AZYIB,1 Nobeyama Radio Observatory: Solar: http://solar.nro.nao.ac.jp/ Keysight Technologies (Agilent, HP) Spectrum Analysis Basics ‐ A Resource Toolkit, a compilation of approximately 40 application notes, videos, mobile apps and web resources: https://www.keysight.com/main/editorial.jspx?cc=US&lc=eng&ckey=2441692&id=2441692&cmpid=473 63 Free online courses through collaboration of Coursera and universities worldwide: https://www.coursera.org/courses Electronics and Electrical Engineering Tools & Calculators: http://www.eeweb.com/toolbox Tektronix ~ Fundamentals of Real‐Time Spectrum Analysis: http://info.tek.com/www‐fundamentals‐of‐ real‐time‐spectrum‐analysis.html 94 Online Resources British Astronomical Association – Radio Astronomy Group Radio Astronomy Supplies http://www.britastro.org/baa/ http://www.radioastronomysupplies.com Radio Sky Publishing CALLISTO Receiver & e‐CALLISTO http://radiosky.com http://www.reeve.com/Solar/e‐CALLISTO/e‐callisto.htm CALLISTO data archive: www.e‐callisto.org Deep Space Exploration Society RF Associates http://dses.org/index.shtml Richard Flagg, [email protected] 1721‐I Young Street, Honolulu, HI 96826 European Radio Astronomy Club RFSpace, Inc http://www.eracnet.org http://www.rfspace.com GNU Radio Shirleys Bay Radio Astronomy Consortium http://www.gnu.org/licenses/gpl.html [email protected] Inspire Project Simple Aurora Monitor Magnetometer http://theinspireproject.org http://www.reeve.com/SAMDescription.htm NASA Radio JOVE Project SETI League http://radiojove.gsfc.nasa.gov http://www.setileague.org Archive: http://radiojove.org/archive.html SkyScan Science Awareness (Meteor Detection) http://www.skyscan.ca/getting_started.htm National Radio Astronomy Observatory Stanford Solar Center http://www.nrao.edu http://solar‐center.stanford.edu/SID/ NRAO Essential Radio Astronomy Course UK Radio Astronomy Association http://www.cv.nrao.edu/course/astr534/ERA.shtml http://www.ukraa.com/www/ Pisgah Astronomical Research Institute SARA Facebook page http://www.pari.edu https://www.facebook.com/pages/Society‐of‐Amateur‐Radio‐ Astronomers/128085007262843 SARA Web Site SARA Twitter feed http://radio‐astronomy.org https://twitter.com/RadioAstronomy1 SARA Email Forum and Discussion Group http://groups.google.com/group/sara‐list 95 For Sale, Trade, and Wanted Sara Polo Shirts SARA has polo shirts with the new SARA logo embroidered. (No pocket) These are 50% cotton and 50% polyester, machine washable. Currently in stock: Size Color Small Navy, Royal Blue Medium Navy, Dark Green, Royal Blue Large Maroon, Black, Navy, Royal Blue X‐Large Maroon, Black, Navy, Royal Blue XX‐Large Maroon, Black, Navy, Dark Green, Royal Blue XXX‐Large Black, Navy, Dark Green, Royal Blue Price is $15 with free shipping in the USA. Additional cost for shipping outside the USA. Other colors and sizes available, contact SARA Treasurer, Melinda Lord, at treasurer@radio‐astronomy.org. There is no charge to place an ad in Radio Astronomy; but, you must be a current SARA member. Ads must be pertinent to radio astronomy and are subject to the editor’s approval and alteration for brevity. Please send your “For Sale,” “Trade,” or “Wanted” ads to editor@radio‐astronomy.org. Please include email and/or telephone contact information. Please keep your ad text to a reasonable length. Ads run for one bimonthly issue unless you request otherwise. For sale Items listed below. Send request to SARA by email to supersid@radio‐astronomy.org. For more information: http://www.radio‐astronomy.org/pdf/sid‐brochure.pdf. Description, items for sale by SARA Price (US$) SuperSID VLF receiver (assembled) $48.00 PCI soundcard, 96 kHz sample rate $40.00 Antenna wire 24 AWG (120 m) $23.00 Coaxial cable, Belden RG58U (9 m) $14.00 Shipping (United States) $10.00 Shipping (Canada, Mexico) $25.00 Shipping (all other) $40.00 96