Signals Volume 09 Number 08 NAAPO (North American AstroPhysical Observatory) "Signals" Volume 9 Number 8 The NAAPO Newsletter (September 1993) NAAPO Coordinator: Editor: Dr. Philip E. Barnhart Earl W. Phillips, Jr. Dept. of Physics/Astronomy 7893 Thornfield Lane Otterbein College Columbus, Ohio 43235 Westerville, Ohio 43081 614-764-0476 614-898-1516 Meetings are held 1st & 3rd Saturdays of each month, beginning at 10:00am; at the office building at the site of the Radio Telescope; and each Tuesday evening starting at 5:00pm, at Room 805, Dreese Hall, OSU Campus. http://www.naapo.org/NAAPO-News/Vol09/v09n08.htm (1 of 14)6/10/2004 12:12:39 PM Signals Volume 09 Number 08 IN THIS ISSUE: ● Summer Intern's Report ● Loch Dixon Mystery Solved ● HRMS Quarterly Report ● Meeting Notes ● JPL Mission Updates ● Mars Observer Update ● Light Pollution Update ● Coordinator's Corner SUMMER INTERN'S REPORT By: Malinda McKay & Chris Slack This summer was a summer of antenna pattern measurements. We started off with something relatively simple, a 2 element beam cut to 1420MHz This was the antenna normally used on the signal squirter. Our reasoning for measuring this antenna was that none of us had ever really done an empirical study of antenna patterns, and a small antenna seemed to be a logical first step before tackling the Big Ear. The setup used for testing the antenna consisted of a transmitter and a receiver. The transmitter was a 1 mW signal source with a 16dB amplifier borrowed from the telescope. The signal was transmitted through the east feedhorn (which was not currently in use). Our receiving setup originally consisted of only the HP power meter and the beam at the end of a 200' extension cord. After taking a few readings and seeing the wild fluctuations we quickly decided that a BP filter was needed. The final setup included a 1390-1430MHz BP filter which eliminated our RFI problems caused by a receiver with an effective bandwidth of 10GHz. At the receiving point we rotated the antenna itself, taking measurements from the power meter every 10°. We then plotted the pattern on polar graph paper and came up with a nice looking plot. Now came the time to do "the real thing" and this antenna would be considerably more difficult to rotate than the little 5" Yagi. In order to avoid rotating the feedhorns (which was never considered) we were planning to move the receiving antenna around the feedhorns, at a constant distance, and with an accurate sense of direction. Doing this with the equipment we had took some mathematics and some very complex measuring devices. For distance we used a 410' piece of nylon cord (which was attached to a strain gauge to assure a constant tension). The angles were determined by calculating the correct 5° cord lengths for a circle with a 410' radius. This method worked and proved to be quite accurate as we were later able to verify by using a transit provided to us by Dr. Barnhart. As we began measuring the feedhorn pattern our receiving setup progressed. We decided, however, not to use the Yagi as the receiving antenna, but instead used a horn-type antenna similar to the skyhorn. Our power source progressed from the 200' of extension cord cobbled together from the RO's supply, to the impressive 500' cord from ESL (which, assuming the parabola is still 410' from the feedhorns, is considerably longer than the reported 500'), and finally to a small lead-acid battery hooked up to the inverter lent to us by Steve Willard which was the best, and final source of power. For the first day of readings the horn was simply held above the ground a few feet, which proved less than ideal. So, a way was needed to raise it up high enough to not be affected by the ground plane. The solution came in the form of a forklift- http://www.naapo.org/NAAPO-News/Vol09/v09n08.htm (2 of 14)6/10/2004 12:12:39 PM Signals Volume 09 Number 08 like piece of equipment from ESL which was laying unused around at the RO, which they call a "genie". This enabled us to raise the horn to a grand height of 14.55' (still not in the principal plane, but high enough to not see too much reflection from the ground plane). This setup provided us with a decent portable receiving device, helping us map the far field from 20° west to 20° east (everything on the ground plane). From the measurements we took in the first 25 weeks we were able to plot the antenna patterns for both the east and west feedhorns from 20° E to 20° W. We also measured 25' distanced on the 0° line in order to determine where the far-field pattern began. It was calculated that the west feedhorn is more sensitive than the east by about 1dB, and that the far field begins at appr. 275'. The remaining week and a half was spent trying to figure out how to do something useful in the field, since time was quickly running out. This proved considerably more difficult than our measurements on the ground plane before. In order to get true measurements we needed to be in the principal plane of the antenna, which in the center of the parabola is at 35'. We also needed to needed to be at a height higher than 14.55' when we went off the ground plane to measure the patterns in the field. Erecting a structure 35' high, which is stable, wind resistant, and portable is not an easy task. We went through several iterations starting with 3 sections of 10' aluminum mast with the 2 element Yagi (modified to be essentially a 3 element Yagi by the addition of a reflector made out of an old high voltage sign). This structure proved to be quite unstable and was never used for measurements. The second structure concerned the genie used for the original measurements with a section of 10' mast attached to it, along with the addition of a discone antenna because the Yagi had proved to be too directional for a true field probing. In order to make this structure more portable it was clamped to an old 2 wheel trailer which was lying around, bringing the total height to about 27'. Upon taking this device into the field and taking some measurements we found nothing. The needle on the meter never budged. The sidelobes were less than -75dB which is the range of the meter. On the next day we had a preamp ready to use with the system. When we brought the system into the field we found that we could see a signal (with an extra 35dB of amplification), but that it varied too much because of the antenna swaying in the wind due to the instability of the structure. We now had one last option; we built "The Thing". The Thing consisted of a base of 4 12' 2x4's, with some support sections and 4 swivel wheels on the bottom to make it semi-portable. The tripod was bolted to The Thing, with 30' of the steel telescoping mast provided for us by Dr. Dixon. The mast was guyed in eight places to the ends of the 4 2x4's (which were layed out in a configuration similar to that of a railroad crossing). The Thing is stable, tall, and amazingly enough, is even portable. Unfortunately, The Thing was completed too late for us to really have a chance to use it much. We were able to see that it should be stable enough to use for measurements, but that was all really. A few more guys wouldn't hurt either. Over the past month we have had a lot of fun and have learned quite a bit. We would like to especially thank Steve Brown & Russ Childers for working with us and teaching us throughout the summer. The teaching we have received will not fall on deaf ears, we promise! We would also like to thank Dr. Barnhart and all of NAAPO for giving us the opportunity to come here this summer and for providing us with experiences that will last a lifetime. Sincerely and with all appreciation; Chris Slack & Malinda McKay. http://www.naapo.org/NAAPO-News/Vol09/v09n08.htm (3 of 14)6/10/2004 12:12:39 PM Signals Volume 09 Number 08 HRMS Quarterly Report - June 1993 By: Ron Baalke Organization: Jet Propulsion Laboratory Forwarded from the HRMS Project NASA HIGH RESOLUTION MICROWAVE SURVEY TARGETED SEARCH AND SKY SURVEY STATUS QUARTERLY REPORT JUNE 1993 BACKGROUND The High Resolution Microwave Survey (HRMS) is part of the Toward Other Planetary Systems (TOPS) program in NASA's Solar System Exploration Division. The HRMS searches for evidence of planets orbiting other stars through radio emissions that may be produced by technological civilizations. The HRMS has two search modes, a Sky Survey and a Targeted Search. The Sky Survey is managed by the Jet Propulsion Laboratory and uses 34-meter antennas in NASA's Deep Space Network to sweep the entire sky over a wide range of frequencies for the presence of strong signals. The Targeted Search uses the largest available radio telescopes to observe nearby Sun-like stars over a narrower range of frequencies for weak signals. The Targeted Search is managed by NASA's Ames Research Center, which is also the lead center for the HRMS. The combination of the two search modes is millions of times more comprehensive than the sum of all previous search programs.