DOCSLIB.ORG

We Help Move Time Through The

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
We Help Move Time Through The 70 RadioWoRld | radioworld.com oPInIon Vol. 35, No. 8 March 23, 2011 Next Issue of RadIo WoRld april 6, 2011 We Help Move Time Through the Air Next Issue of ENgINEERINg ExtRa april 13, 2011 E-mail: [email protected] Web site: www.radioworld.com Managers of WWVB Explore Options to Improve the Service Further telephone: (703) 852-4600 Business Fax: (703) 852-4582 ◗commentary Editorial Fax: (703) 852-4585 For address changes and subscription renewal, please visit radioworld.com and click on the “Subscription” button. by John lowe to submit letters or story proposals, to request writer’s guidelines, or for other editorial matters, e-mail the editor at [email protected]. The author is manager of National EDITORIAL STAFF Institute of Standards and Technology EdItoR IN ChIEF, U.S. Paul J. Mclane radio stations WWV/WWVH/WWVB. NEWS EdItoR/WaSh. BUREaU ChIEF leslie Stimson gEaR & tEChNology EdItoR Brett Moss tEChNICal adVISER thomas R. Mcginley While radio station WWVB may tEChNICal EdItoR, RWEE Michael leClair be familiar to readers of this publica- PRodUCtIoN EdItoR, RWEE Karen lee CoNtRIBUtINg EdItoR John Bisset tion, most people would not recognize INtERNatIoNal EdItoR IN ChIEF t. Carter Ross those call letters. However, if you say latIN aMERICa EdItoR IN ChIEF Rogelio ocampo latIN aMERICa EdItoR Karina gerardi you have an “atomic clock” hanging on MaNagINg EdItoR, WEB Brian Smith the wall of your house, most everyone EDITORIAL CONTRIBUTORS would know what you meant. W.C. alexander, Barry Blesser, James Careless, harry Cole, Of course it is not a real atomic Ken deutsch, Mark durenberger, Charles Fitch, ty Ford, harold hallikainen, Craig Johnston, Paul Kaminski, Peter King, Mark lapidus, clock, but a radio-controlled device that daniel Man sergh, John Merli, laura Mir, Mark Persons, Sharon Rae receives the WWVB signal and corrects Pettigrew, Stephen M. Poole, Carl lindemann, ted Nahil, James itself nightly when the 60 kHz signal o’Neal, tom osenkowsky, Rich Rarey, tom Ray, John Schneider, Randy Stine, Richard Strickland, James g. Withers, tom Vernon propagates the best. The antenna towers of WWVB in Fort Collins, Colo. In July 1956 the National Bureau of ADMINISTRATION & PRODUCTION PUBlIShER John Casey Standards started radio station KK2XEI alkalinity of the soil. the top hat is much less than a quarter EdItoRIal dIRECtoR t. Carter Ross in Boulder, Colo. It was a 2 kW trans- On July 5, 1963, WWVB began broad- wavelength. Therefore, the top hat is PRodUCtIoN dIRECtoR davis White PRodUCtIoN PUBlICatIoN CooRdINatoR Karen lee mitter sending a 60 kHz signal into the casting a 7 kW signal at 60 kHz. In August inherently capacitive and a large induc- adVERtISINg CooRdINatoR Caroline Freeland summer sky. Even though the effective of that year, its sister station, WWVL, tor is added in the helix house to cancel CIRCULATION radiated power was less than 2 watts, began broadcasting a 500 W signal at 20 the capacitance of the short antenna. A aSSoCIatE CIRCUlatIoN dIRECtoR, the signal was received and monitored kHz. On July 1, 1965, WWVB added a variometer, or variable inductor, is also aUdIENCE dEVEloPMENt tracey dwyer at Harvard University in Massachusetts. time code to the broadcast. included in the helix house to tune the CIRCUlatIoN MaNagER Kwentin Keenan CIRCUlatIoN CooRdINatoR Michele Fonville antenna, which is especially useful dur- ing wind and ice loading. SUBSCRIPTIONS Radio World, P.o. Box 282, lowell, Ma 01853 In 1997, work began to improve tElEPhoNE: 888-266-5828 (USa only 8:30 a.m.–5 p.m. ESt) An idea being actively investigated is to add the WWVB broadcast. More powerful 978-667-0352 (outside the US) Fax: 978-671-0460 transmitters (FRT-72) were acquired WEB SItE: www.myRWNews.com E-MaIl: [email protected] phase modulation to the existing WWVB signal while from U.S. Navy surplus in Virginia, Scotland and Iceland. Extended tuning CORPORATE leaving the aM BCd code intact. NewBay Media llC variometers were acquired from the PRESIdENt aNd CEo Steve Palm decommissioned Navy low-frequency ChIEF FINaNCIal oFFICER Paul Mastronardi CoNtRollER Jack liedke station NSS in Annapolis, Md. gRoUP CIRCUlatIoN dIRECtoR denise Robbins This experiment showed that the fre- The binary-coded decimal (BCD) The WWVB broadcast was kept on VICE PRESIdENt oF WEB dEVEloPMENt Joe Ferrick quency error due to the Doppler shift time code transmitted 1 bit per second the air during these upgrades by use VIDEO /BROADCAST GROUP induced by the ionosphere was small. by shifting the power of the carrier by of the old WWVL antenna. When the ExECUtIVE VICE PRESIdENt Carmel King This was the forerunner of the WWVB 10 dB. The format is explained in the upgrades were complete on the WWVB VICE PRESIdENt / SalES dIRECtoR Eric trabb broadcast. accompanying graphic on page 69. side, the WWVL side was upgraded and ADVERTISING SALES REPRESENTATIVES US EaSt & latIN aMERICa: John Casey, [email protected] In April 1960 another experiment Over the next few years, improve- they were combined with WWVB into t: 212-378-0400, ext. 512 | F: 330-247-1288 was conducted in the foothills of the ments were made to increase the power a dual broadcast system. Broadcasting US WESt & CaNada: david Carson, [email protected] mountains west of Boulder. A valley- up to approximately 13 kW, and it from both antennas, the WWVB signal t: 212-378-0400, ext. 511 | F: 866-572-6156 SoUthERN EURoPE, aFRICa, MIddlE EaSt: span antenna 3,400 feet long was strung remained there until the late 1990s. In was boosted to 50 kW of effective radi- Raffaella Calabrese, [email protected] near the old mining town of Sunset. The 1972, the WWVL broadcast was termi- ated power beginning in 1999. t: +39-02-7030-0310 | F: +39-02-7030-0211 UK & IRElaNd, CENtRal & NoRthERN EURoPE: signal was broadcast with less than 15 nated and its antenna became the rarely This increase in power created an graham Kirk, [email protected] watts of power, yet it was consistently used WWVB backup antenna. explosion of new commercial radio- t: +44-1480-461555 | F: +44-1480-461550 observed in New Zealand. Each antenna is a top-loaded dipole controlled products, more than a million JaPaN: Eiji yoshikawa, [email protected] t: +81-3-3327-5759 | F: +81-3-3322-7933 Results from the Sunset experiment consisting of four 122-meter (400-foot) of which are sold each year. aSIa-PaCIFIC: Wengong Wang, [email protected] provided a much better understanding towers arranged in a diamond shape. t: +86-755-83862930/40/50 | F: +86-755-83862920 AnOtheR stAtIOn? ClaSSIFIEdS: david Carson, [email protected] of the ionosphere and the study of Suspended between the four towers is t: 212-378-0400, ext. 511 | F: 866-572-6156 whistlers, hiss, the dawn chorus and a system of aluminum cables called a Despite the overall quality and reli- “sferics.” capacitance hat or “top hat.” The top ability of these products, there are times Radio World Founded by Stevan B. dana This set the stage for the WWVB hat is electrically isolated from the tow- and locations at which the WWVB Radio World (ISSN: 0274-8541) is published bi-weekly with additional issues in February, april, June, august, october and radio station. ers, but connected to a down-lead at the signal is not well received or decoded december by NewBay Media, llC, 28 East 28th Street, New center of the diamond. The down-lead is properly. york, Ny 10016. Phone: (703) 852-4600, Fax: (703) 852-4582. tIme’s tOP hAt Periodicals postage rates are paid at New york, Ny 10079 and the radiating element emanating from a This is due to distance from the additional mailing offices. PoStMaStER: Send address changes to Construction began in 1962 on a site helix house at ground level and also at transmitter and also interference (added Radio World, P.o. Box 282, lowell, Ma 01853. north of Fort Collins, Colo., near the the center of the diamond. noise) to the signal caused by near- REPRINtS: Call or write Caroline Freeland, 5285 Shawnee Rd., small town of Wellington. The 390- The wavelength of a 60 kHz signal is by radiating sources such as computer Ste. 100, alexandria, Va 22312-2334; (703) 852-4600; acre site was chosen in part for its high nearly 5,000 m (more than 3 miles), so monitors or power transformers. To Fax: (703) 852-4583 (continued on page 69) ground conductivity, a result of the high the length of the radiating element plus globe graphic ©iStockphoto.com / Edward grajeda Copyright 2011 by NewBay Media, llC. all rights reserved. Printed in the USa 69 This listing is provided for the convenience of our readers. AdveRtIseR Index Radio World assumes no liability for inaccuracy. oPinion RadioWoRld March 23, 2011 page advertiser web site/url 56 acoustics First Corp www.acousticsfirst.com frequencies from the same location 43 aeQ, Sa www.aeqbroadcast.com WWVB improves the chances of receiving at (continued from page 70) least one of the signals because the 50 aM Ground Systems Co. www.amgroundsystems.com transmission nulls are related to fre- 12 armstrong transmitter Co. www.armstrongtx.com help improve this situation, the trans- quency and therefore should occur in 62 audio technica www.audio-technica.com mitted power was increased about five different locations. Also, interference 5 audioScience Inc. www.audioscience.com years ago to 70 kW and the modulation may be affecting only one frequency at 57 axia - a telos Company www.axiaaudio.com depth was increased from 10 dB to 17 a given location. A receiver would need dB. This helped, but has not solved the to determine which signal is strongest or 63 Besco Internacional www.besco-int.com inherent problem of a poor signal-to- more readable.
Load more

Recommended publications
  • WWVB: a Half Century of Delivering Accurate Frequency and Time by Radio
    Volume 119 (2014) http://dx.doi.org/10.6028/jres.119.004 Journal of Research of the National Institute of Standards and Technology WWVB: A Half Century of Delivering Accurate Frequency and Time by Radio Michael A. Lombardi and Glenn K. Nelson National Institute of Standards and Technology, Boulder, CO 80305 [email protected] [email protected] In commemoration of its 50th anniversary of broadcasting from Fort Collins, Colorado, this paper provides a history of the National Institute of Standards and Technology (NIST) radio station WWVB. The narrative describes the evolution of the station, from its origins as a source of standard frequency, to its current role as the source of time-of-day synchronization for many millions of radio controlled clocks. Key words: broadcasting; frequency; radio; standards; time. Accepted: February 26, 2014 Published: March 12, 2014 http://dx.doi.org/10.6028/jres.119.004 1. Introduction NIST radio station WWVB, which today serves as the synchronization source for tens of millions of radio controlled clocks, began operation from its present location near Fort Collins, Colorado at 0 hours, 0 minutes Universal Time on July 5, 1963. Thus, the year 2013 marked the station’s 50th anniversary, a half century of delivering frequency and time signals referenced to the national standard to the United States public. One of the best known and most widely used measurement services provided by the U. S. government, WWVB has spanned and survived numerous technological eras. Based on technology that was already mature and well established when the station began broadcasting in 1963, WWVB later benefitted from the miniaturization of electronics and the advent of the microprocessor, which made low cost radio controlled clocks possible that would work indoors.
    [Show full text]
  • Reception of Low Frequency Time Signals
    Reprinted from I-This reDort show: the Dossibilitks of clock svnchronization using time signals I 9 transmitted at low frequencies. The study was madr by obsirvins pulses Vol. 6, NO. 9, pp 13-21 emitted by HBC (75 kHr) in Switxerland and by WWVB (60 kHr) in tha United States. (September 1968), The results show that the low frequencies are preferable to the very low frequencies. Measurementi show that by carefully selecting a point on the decay curve of the pulse it is possible at distances from 100 to 1000 kilo- meters to obtain time measurements with an accuracy of +40 microseconds. A comparison of the theoretical and experimental reiulb permib the study of propagation conditions and, further, shows the drsirability of transmitting I seconds pulses with fixed envelope shape. RECEPTION OF LOW FREQUENCY TIME SIGNALS DAVID H. ANDREWS P. E., Electronics Consultant* C. CHASLAIN, J. DePRlNS University of Brussels, Brussels, Belgium 1. INTRODUCTION parisons of atomic clocks, it does not suffice for clock For several years the phases of VLF and LF carriers synchronization (epoch setting). Presently, the most of standard frequency transmitters have been monitored accurate technique requires carrying portable atomic to compare atomic clock~.~,*,3 clocks between the laboratories to be synchronized. No matter what the accuracies of the various clocks may be, The 24-hour phase stability is excellent and allows periodic synchronization must be provided. Actually frequency calibrations to be made with an accuracy ap- the observed frequency deviation of 3 x 1o-l2 between proaching 1 x 10-11. It is well known that over a 24- cesium controlled oscillators amounts to a timing error hour period diurnal effects occur due to propagation of about 100T microseconds, where T, given in years, variations.
    [Show full text]
  • Analog Clock Headway Movement FAQS
    ANALOG CLOCK HEADWAY MOVEMENT FAQS The links below will work in most PDF viewers and link to the topic area by clicking the link. We recommend Adobe Reader version 10 or greater available at: http://get.adobe.com/reader CONTENTS Analog Clock Headway Movement FAQS .................................................................... 1 Batteries ............................................................................................................................. 2 Atomic Clock Factory Restart ...................................................................................... 2 Supported Time Zones .................................................................................................. 2 Time is Incorrect ............................................................................................................. 2 Clock is incorrect by Hours but minutes are correct .......................................... 3 Daylight Saving Time ..................................................................................................... 3 Manually Set Time ........................................................................................................... 3 How long will the battery last? .................................................................................. 3 Can I shut off the WWVB signal? .............................................................................. 3 Is there a booster antenna to receive the WWVB signal in a difficult location? ............................................................................................................................
    [Show full text]
  • Five Years of VLF Worldwide Comparison of Atomic Frequency Standards
    RADIO SCIENCE, Vol. 2 (New Series), No. 6, June 1967 Five Years of VLF Worldwide Comparison of Atomic Frequency Standards B. E. Blair,' E. 1. Crow,2 and A. H. Morgan (Received January 19, 1967) The VLF radio broadcasts of GBR(16.0 kHz), NBA(18.0 or 24.0 kHz), and NSS(21.4 kHz) have enabled worldwide comparisons of atomic frequency standards to parts in 1O'O when received over varied paths and at distances up to 9000 or more kilometers. This paper summarizes a statistical analysis of such comparison data from laboratories in England, France, Switzerland, Sweden, Russia, Japan, Canada, and the United States during the 5-year period 1961-1965. The basic data are dif- ferences in 24-hr average frequencies between the local atomic standard and the received VLF radio signal expressed as parts in 10"'. The analysis of the more recent data finds the receiving laboratory standard deviations, &, and the transmission standard deviation, ?, to be a few parts in 10". Averag- ing frequencies over an increasing number of days has the effect of reducing iUi and ? to some extent. The variation of the & with propagation distance is studied. The VLF-LF long-term mean differences between standards are compared with the recent portable clock tests, and they agree to parts in IO". 1. Introduction points via satellites (Steele, Markowitz, and Lidback, 1964; Markowitz, Lidback, Uyeda, and Muramatsu, Six years ago in London, the XIIIth General Assem- 1966); improvements in the transmission of VLF and bly of URSI adopted a resolution (No. 2) which strongly LF radio signals (Milton, Fey, and Morgan, 1962; recommended continuous very-low-frequency (VLF) Barnes, Andrews, and Allan, 1965; Bonanomi, 1966; and low-frequency (LF) transmission monitoring US.
    [Show full text]
  • High Frequency (HF)
    Calhoun: The NPS Institutional Archive Theses and Dissertations Thesis Collection 1990-06 High Frequency (HF) radio signal amplitude characteristics, HF receiver site performance criteria, and expanding the dynamic range of HF digital new energy receivers by strong signal elimination Lott, Gus K., Jr. Monterey, California: Naval Postgraduate School http://hdl.handle.net/10945/34806 NPS62-90-006 NAVAL POSTGRADUATE SCHOOL Monterey, ,California DISSERTATION HIGH FREQUENCY (HF) RADIO SIGNAL AMPLITUDE CHARACTERISTICS, HF RECEIVER SITE PERFORMANCE CRITERIA, and EXPANDING THE DYNAMIC RANGE OF HF DIGITAL NEW ENERGY RECEIVERS BY STRONG SIGNAL ELIMINATION by Gus K. lott, Jr. June 1990 Dissertation Supervisor: Stephen Jauregui !)1!tmlmtmOlt tlMm!rJ to tJ.s. eave"ilIE'il Jlcg6iielw olil, 10 piolecl ailicallecl",olog't dU'ie 18S8. Btl,s, refttteste fer litis dOCdiii6i,1 i'lust be ,ele"ed to Sapeihil6iiddiil, 80de «Me, "aial Postg;aduulG Sclleel, MOli'CIG" S,e, 98918 &988 SF 8o'iUiid'ids" PM::; 'zt6lI44,Spawd"d t4aoal \\'&u 'al a a,Sloi,1S eai"i,al'~. 'Nsslal.;gtePl. Be 29S&B &198 .isthe 9aleMBe leclu,sicaf ,.,FO'iciaKe" 6alite., ea,.idiO'. Statio", AlexB •• d.is, VA. !!!eN 8'4!. ,;M.41148 'fl'is dUcO,.Mill W'ilai.,s aliilical data wlrose expo,l is idst,icted by tli6 Arlil! Eurse" SSPItial "at FRIis ee, 1:I.9.e. gec. ii'S1 sl. seq.) 01 tlls Exr;01l ftle!lIi"isllatioli Act 0' 19i'9, as 1tI'I'I0"e!ee!, "Filill ell, W.S.€'I ,0,,,,, 1i!4Q1, III: IIlIiI. 'o'iolatioils of ltrese expo,lla;;s ale subject to 960616 an.iudl pSiiaities.
    [Show full text]
  • NIST Time and Frequency Services (NIST Special Publication 432)
    Time & Freq Sp Publication A 2/13/02 5:24 PM Page 1 NIST Special Publication 432, 2002 Edition NIST Time and Frequency Services Michael A. Lombardi Time & Freq Sp Publication A 2/13/02 5:24 PM Page 2 Time & Freq Sp Publication A 4/22/03 1:32 PM Page 3 NIST Special Publication 432 (Minor text revisions made in April 2003) NIST Time and Frequency Services Michael A. Lombardi Time and Frequency Division Physics Laboratory (Supersedes NIST Special Publication 432, dated June 1991) January 2002 U.S. DEPARTMENT OF COMMERCE Donald L. Evans, Secretary TECHNOLOGY ADMINISTRATION Phillip J. Bond, Under Secretary for Technology NATIONAL INSTITUTE OF STANDARDS AND TECHNOLOGY Arden L. Bement, Jr., Director Time & Freq Sp Publication A 2/13/02 5:24 PM Page 4 Certain commercial entities, equipment, or materials may be identified in this document in order to describe an experimental procedure or concept adequately. Such identification is not intended to imply recommendation or endorsement by the National Institute of Standards and Technology, nor is it intended to imply that the entities, materials, or equipment are necessarily the best available for the purpose. NATIONAL INSTITUTE OF STANDARDS AND TECHNOLOGY SPECIAL PUBLICATION 432 (SUPERSEDES NIST SPECIAL PUBLICATION 432, DATED JUNE 1991) NATL. INST.STAND.TECHNOL. SPEC. PUBL. 432, 76 PAGES (JANUARY 2002) CODEN: NSPUE2 U.S. GOVERNMENT PRINTING OFFICE WASHINGTON: 2002 For sale by the Superintendent of Documents, U.S. Government Printing Office Website: bookstore.gpo.gov Phone: (202) 512-1800 Fax: (202)
    [Show full text]
  • Correlation of Very Low and Low Frequency Signal Variations at Mid-Latitudes with Magnetic Activity and Outer-Zone Particles
    Ann. Geophys., 32, 1455–1462, 2014 www.ann-geophys.net/32/1455/2014/ doi:10.5194/angeo-32-1455-2014 © Author(s) 2014. CC Attribution 3.0 License. Correlation of very low and low frequency signal variations at mid-latitudes with magnetic activity and outer-zone particles A. Rozhnoi1, M. Solovieva1, V. Fedun2, M. Hayakawa3, K. Schwingenschuh4, and B. Levin5 1Institute of Physics of the Earth, Russian Academy of Sciences, 10 B. Gruzinskaya, Moscow, 123995, Russia 2Space Systems Laboratory, Department of Automatic Control and Systems Engineering, University of Sheffield, Sheffield, S1 3JD, UK 3University of Electro-Communications, Advanced Wireless Communications Research Center, 1-5-1 Chofugaoka, Chofu Tokyo, 182-8585, Japan 4Space Research Institute, Austrian Academy of Sciences, 6 Schmiedlstraße, 8042, Graz, Austria 5Institute of marine geology and geophysics Far East Branch of Russian Academy of Sciences, 1B Nauki str., Yuzhno-Sakhalinsk, 693022, Russia Correspondence to: A. Rozhnoi ([email protected]) Received: 31 May 2014 – Revised: 28 October 2014 – Accepted: 31 October 2014 – Published: 4 December 2014 Abstract. The disturbances of very low and low frequency Hayakawa, 2008; Hayakawa et al., 2010; Hayakawa, 2011; signals in the lower mid-latitude ionosphere caused by mag- Biagi et al., 2004, 2007; Rozhnoi et al., 2004, 2009). This netic storms, proton bursts and relativistic electron fluxes band of electromagnetic waves is trapped between the lower are investigated on the basis of VLF–LF measurements ob- ionosphere and the surface of the Earth, and reflected from tained in the Far East and European networks. We have found the boundary between the upper atmosphere and lower iono- that magnetic storm (−150 < Dst < −100 nT) influence is sphere at altitudes of ≈ 70 km (daytime) and ≈ 90 km (night- not strong on variations of VLF–LF signals.
    [Show full text]
  • Identifying and Removing Tilt Noise from Low-Frequency (0.1
    Bulletin of the Seismological Society of America, 90, 4, pp. 952–963, August 2000 Identifying and Removing Tilt Noise from Low-Frequency (Ͻ0.1 Hz) Seafloor Vertical Seismic Data by Wayne C. Crawford and Spahr C. Webb Abstract Low-frequency (Ͻ0.1 Hz) vertical-component seismic noise can be re- duced by 25 dB or more at seafloor seismic stations by subtracting the coherent signals derived from (1) horizontal seismic observations associated with tilt noise, and (2) pressure measurements related to infragravity waves. The reduction in ef- fective noise levels is largest for the poorest stations: sites with soft sediments, high currents, shallow water, or a poorly leveled seismometer. The importance of precise leveling is evident in our measurements: low-frequency background vertical seismic radians 4מ10 ן spectra measured on a seafloor seismometer leveled to within 1 (0.006 degrees) are up to 20 dB quieter than on a nearby seismometer leveled to radians (0.2 degrees). The noise on the less precisely leveled sensor 3מ10 ן within 3 increases with decreasing frequency and is correlated with ocean tides, indicating that it is caused by tilting due to seafloor currents flowing across the instrument. At low frequencies, this tilting generates a seismic signal by changing the gravitational attraction on the geophones as they rotate with respect to the earth’s gravitational field. The effect is much stronger on the horizontal components than on the vertical, allowing significant reduction in vertical-component noise by subtracting the coher- ent horizontal component noise. This technique reduces the low-frequency vertical noise on the less-precisely leveled seismometer to below the noise level on the pre- cisely leveled seismometer.
    [Show full text]
  • The Effect of the Ionosphere on Ultra-Low-Frequency Radio-Interferometric Observations? F
    A&A 615, A179 (2018) Astronomy https://doi.org/10.1051/0004-6361/201833012 & © ESO 2018 Astrophysics The effect of the ionosphere on ultra-low-frequency radio-interferometric observations? F. de Gasperin1,2, M. Mevius3, D. A. Rafferty2, H. T. Intema1, and R. A. Fallows3 1 Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands e-mail: [email protected] 2 Hamburger Sternwarte, Universität Hamburg, Gojenbergsweg 112, 21029 Hamburg, Germany 3 ASTRON – the Netherlands Institute for Radio Astronomy, PO Box 2, 7990 AA Dwingeloo, The Netherlands Received 13 March 2018 / Accepted 19 April 2018 ABSTRACT Context. The ionosphere is the main driver of a series of systematic effects that limit our ability to explore the low-frequency (<1 GHz) sky with radio interferometers. Its effects become increasingly important towards lower frequencies and are particularly hard to calibrate in the low signal-to-noise ratio (S/N) regime in which low-frequency telescopes operate. Aims. In this paper we characterise and quantify the effect of ionospheric-induced systematic errors on astronomical interferometric radio observations at ultra-low frequencies (<100 MHz). We also provide guidelines for observations and data reduction at these frequencies with the LOw Frequency ARray (LOFAR) and future instruments such as the Square Kilometre Array (SKA). Methods. We derive the expected systematic error induced by the ionosphere. We compare our predictions with data from the Low Band Antenna (LBA) system of LOFAR. Results. We show that we can isolate the ionospheric effect in LOFAR LBA data and that our results are compatible with satellite measurements, providing an independent way to measure the ionospheric total electron content (TEC).
    [Show full text]
  • The Emergence of Low Frequency Active Acoustics As a Critical
    Low-Frequency Acoustics as an Antisubmarine Warfare Technology GORDON D. TYLER, JR. THE EMERGENCE OF LOW–FREQUENCY ACTIVE ACOUSTICS AS A CRITICAL ANTISUBMARINE WARFARE TECHNOLOGY For the three decades following World War II, the United States realized unparalleled success in strategic and tactical antisubmarine warfare operations by exploiting the high acoustic source levels of Soviet submarines to achieve long detection ranges. The emergence of the quiet Soviet submarine in the 1980s mandated that new and revolutionary approaches to submarine detection be developed if the United States was to continue to achieve its traditional antisubmarine warfare effectiveness. Since it is immune to sound-quieting efforts, low-frequency active acoustics has been proposed as a replacement for traditional passive acoustic sensor systems. The underlying science and physics behind this technology are currently being investigated as part of an urgent U.S. Navy initiative, but the United States and its NATO allies have already begun development programs for fielding sonars using low-frequency active acoustics. Although these first systems have yet to become operational in deep water, research is also under way to apply this technology to Third World shallow-water areas and to anticipate potential countermeasures that an adversary may develop. HISTORICAL PERSPECTIVE The nature of naval warfare changed dramatically capability of their submarine forces, and both countries following the conclusion of World War II when, in Jan- have come to regard these submarines as principal com- uary 1955, the USS Nautilus sent the message, “Under ponents of their tactical naval forces, as well as their way on nuclear power,” while running submerged from strategic arsenals.
    [Show full text]
  • Popular $2.50 Canada
    ICD-08635 JUNE 1986 $1.95 POPULAR $2.50 CANADA Now Incorporating SeSC011 Magazine The Official Publication of the Scanner Association of North America www.americanradiohistory.com ASLEEP...AWAY...ON-THE-JOB... DON'T MISS ANYTHING ON YOUR SCANNER Exclusive! Monitor volume Exclusive! Voice -tailored Exclusive! Delay time con- control is independent of speaker system for trol adjusts to hold for recording volume. listening clarity. reply messages. Exclusive! VOX level light Exclusive! Attractive assures perfect adjustment. molded high -impact cabinetry. A.do 11.,,_ 00e10110110) U.L. listed power supply ERTM included. TrJer:Activator A permanent record even when you're Hear while you record. not there! "What used to drive me crazy was that MONEY BACK GUARANTEE "Before I installed NiteLogger I always anytime the recorder was plugged into If you're dissatisfied in any way with seemed to miss the big stories'..." Now the scanner, the speaker was cut-off so Nitelogger, just return it to us prepaid solve the biggest frustration of scanner I couldn't hear what was going on!" within 25 days for a prompt, courteous enthusiasts: NiteLogger makes sure you'll NiteLogger's built-in monitor speaker and refund. For One Full Year NiteLogger hear it all, even if it happens at 3:47 a.m.! Monitor Level control solves the problem. is guaranteed to be free of defects in Foolproof operation...works every You control the volume from off to full on, workmanship and materials. Simply time! independent of recording levels. send prepaid to BMI for warranty repair. "I've tried rigging up recorders before only Buy with absolute confidence.
    [Show full text]
  • Radio Navigational Aids
    RADIO NAVIGATIONAL AIDS Publication No. 117 2014 Edition Prepared and published by the NATIONAL GEOSPATIAL-INTELLIGENCE AGENCY Springfield, VA © COPYRIGHT 2014 BY THE UNITED STATES GOVERNMENT NO COPYRIGHT CLAIMED UNDER TITLE 17 U.S.C. WARNING ON USE OF FLOATING AIDS TO NAVIGATION TO FIX A NAVIGATIONAL POSITION The aids to navigation depicted on charts comprise a system consisting of fixed and floating aids with varying degrees of reliability. Therefore, prudent mariners will not rely solely on any single aid to navigation, particularly a floating aid. The buoy symbol is used to indicate the approximate position of the buoy body and the sinker which secures the buoy to the seabed. The approximate position is used because of practical limitations in positioning and maintaining buoys and their sinkers in precise geographical locations. These limitations include, but are not limited to, inherent imprecisions in position fixing methods, prevailing atmospheric and sea conditions, the slope of and the material making up the seabed, the fact that buoys are moored to sinkers by varying lengths of chain, and the fact that buoy and/or sinker positions are not under continuous surveillance but are normally checked only during periodic maintenance visits which often occur more than a year apart. The position of the buoy body can be expected to shift inside and outside the charting symbol due to the forces of nature. The mariner is also cautioned that buoys are liable to be carried away, shifted, capsized, sunk, etc. Lighted buoys may be extinguished or sound signals may not function as the result of ice or other natural causes, collisions, or other accidents.
    [Show full text]