Low Power 2-Meter EME Contact by Bob Larkin W7PUA boblark@proaxis.com 6 May 2001 This is the "long version" of the 2-meter PUA43 mode Moonbounce(EME) contact between my brother Beb Larkin, W7SLB, and myself. DSP aided reception was used and the signals were much too weak to allow them to be heard by ear, To our knowledge, this QSO used the smallest stations that have been successful for Moonbounce at this frequency. Reports to the contrary would ge greatly appreciated. What follows are probably more details than most people care to hear about, but for those that want to try similar experiments, this may be useful! W7SLB, Eatonville, WA DSP-10 transceiver used with a conventional PC, An 18 foot, K1FO type of Yagi is used with circular polarization, so there are actually 24 elements, 12 for each of two orthoganol linear Yagis. The Yagis are on two separate booms that are fastened together to make a single circularly polarized antenna. Circular polarization is formed by a four-coax-line quarter-wave hybrid using 35 Ohm and 50 Ohm coax. Two 70 Ohm coaxes are paralleled to make 35 Ohm coax. An 8-Watt "Brickette" (June 2000 QST) drives an older KLM 150 Watt amplifier, driven to 140 Watts max output. A fan is used to cool the amplifier for the continuous duty of the PUA43 mode. Never-the-less, the output drops to as low as 100 Watts when run continuously. A Janel QSA-5 (measured 2.0 dB NF, 17.5 dB gain) is mounted at the hybrid, along with a termination that is relay switched in to replace the preamp when in transmit. A second QSA-5 is mounted in the shack to make sure that the lowest NF is attained. An HP 10811 crystal oscillator is used as a frequency reference. This holds 1 Hz or better at 144 MHz when set on frequency. The transmitter feedline is 20 feet of RG-213 and has an estimated loss of 0.6 dB. W7SLB's location is semi-rural. He is about a mile from Eatonville and can see many houses, but they are all on multiple acre tracts. He has no extreme birdy or line-noise problems. One measurement of his quiet-sky temperature at 144 MHz showed about 500 K. Estimated station ERP is 3500 Watts, max. W7PUA, Corvallis, OR A DSP- 10 transceiver is used with a conventional PC. One M-Squared 2MXP28 34'-6" circularly polarized Yagi. The same hybrid arrangement as used by W7SLB. An 8-Watt "Brickette" drives a Mirage B1016 to 150 Watts max output. Feedlines were about 8 feet. Output drops to about 130 Watts with continuous operation. A home built GaAs-FET preamp (measured 0.7 dB NF, 18 dB gain) was at the antenna. Transmission lines back to the DSP-10 were about 150 feet. This is necessary to reach the portion of the yard without oak trees. Feedline losses were not important since the receiver preamp and transmitter amplifiers were at the antenna. W7PUA's location is within the city of Corvallis (50,000 people). A 69 kV power line, about a block away, causes noise in the antenna sidelobes when the weather is dry, as it has been lately. The quiet sky was measured at 750 K. General noise and birdy interference are observed at low elevation angles. Estimated station ERP is 7200 Watts, max. The Path It is about 175 miles between the stations with lots of big hills and small mountains (including Mt St. Helens). With both antennas pointed at the Moon there is very little signal between the two stations. For reasons that have been discussed on the DSP-10 email reflector, there is no possibility of having a PUA43 contact that is not reflected from the Moon. Background and the Objective Moonbounce has become common for stations running large antennas and power in the 1000 or 1500 Watt range. Smaller stations have been able to work larger stations. For example, K6PF reports that using 175 Watts and a single Yagi in the class of W7SLB's (but with linear polarization), he has been successful in working AA4FO with 8 Yagis. K6PF is in a noisy LA location. The QSO required 22 cumulative hours for the QSO! Large antennas and high power are often not compatible with urban amateur radio operation. The weak-signal capabilities of the DSP-10 suggest that it might be possible to achieve EME capability with urban-friendly equipment! We defined this to be a single Yagi and 150 Watts of power. For this to be generally useful, the same requirements were placed on both ends of the contact. The objective of the QSO was to demonstrate the feasibility of using a simple, urban-friendly setup to achieve Moonbounce contacts. What is a QSO? We tried to meet the requirements of a QSO: Exchange Call Signs Exchange information (We used Grid Squares) Acknowledge reception of the above. We did not try to place any other limits on the QSO. In particular, we used as much time as we needed and also used 75 meters to coordinate the work. We are aware that in some peoples judgement, this is not a "real" QSO. We too would like to do a fast contact without external coordination, and this may be possible in the future, However, as neophytes at both EME and using the PUA43 mode, it seemed best that we start with the generally accepted requirements of a QSO and not add any others. Operation During the QSO We had hoped to try for a QSO on 30 April, 2001, but the weather did not cooperate and so we waited for an end to the rain and wind in Washington. On Wednesday, 2 May the weather improved and we set up the gear at the antennas that were already in our yards. By the time we got started it was 3 May in Greenwich and the date/times listed here will all be in UT (GMT). Starting at 0030Z on 3 May, we both tried EME2 transmissions with little success. The Moon was only 20-25 degrees elevation and noise was a problem. When the moon got up around 52 degrees elevation, W7SLB switched to LTI transmission which maximizes the S/N to see if a signal was present. I was receiving him with about 1 dB S+N/N, which usually supports PUA43 in a reasonable amount of time. So we switched to 14 character PUA43 mode and Beb started to send at 0400Z. In one hour I had received call signs and grid square from Beb, but two of the characters were in the "top row" meaning that they were the second most likely symbols. We allow this, but hoped to get all symbols to the bottom primary row. This took an additional 40 minutes. Both birdies and power line interference were causing trouble in copying Beb, but we have no simple way of knowing how much. Next I sent PUA43 to Beb. But he got no copy, so we gave up for the night. Thursday night we started again, but Beb got no copy. We switched to LTI and still got no signal through. We were trying to imagine what the problem was, as everything seemed to be set up properly. Finally, we found that there is a problem with the software for the PUA43 mode. If the data on the bottom line is set for Sun data and the EME Doppler corrections are enabled, no correction is made. The receiver frequency shows the same as the transmitter frequency, so if one watches this they will be aware of the problem. By the time we discovered this it was getting late. At about 0545Z on 4 May I started to send PUA43 to Beb. He got some copy fairly quickly, but was missing one letter of my call sign until 0850Z. This was right at the time that Beb lost the ability to "see" the Moon and the end of his coax length as well! So we stopped for the evening. The next night we exchanged multiple R's with some difficulty, primarily because of line noise at W7PUA. But we felt that a demonstration was successful. The elapsed time for the four transmissions were: W7SLB to W7PUA Calls and grid 100 minutes W7PUA to W7SLB Calls and grid 169 minutes W7PUA to W7SLB Acknowledgement 15 minutes W7SLB to W7PUA Acknowledgement 110 minutes ---- Total transmission time 394 minutes This is about 6-1/2 hours. Obviously the total time spent at the activity was much greater, about 2-1/2 full evenings! Improvements At one point, Beb lost quite a bit of good copy when an automatic sodium vapor light came on. At another point a Makita hand drill caused the loss of data. The need for a Noise Blanker in the PUA43 mode was obvious! Such software is in the EME2 and LTI modes. A similar noise blanker was adapted to the PUA43 mode after the QSO, so the next ones won't have as many noise problems as we did. A few more dB would really help. A 3 dB increase in antenna gain cuts the amount of time required by a factor of 4. Beb's antenna was modest in size and most back yards would hold something more like the M2 antenna at W7PUA adding 2.5 or 3 dB both ways. Our transmitter power seemed to be limited by the drive from the Brickette. This needs to be worked on to make sure that the full 150 Watts is being achieved. This is probably good for 1 to 2 dB. And like any activity, we require practice to be at our best. This was only our second PUA43 QSO off the Moon and I for one did not feel like an expert! A narrower vertical beamwidth would be helpful for people living in a noisy location. Our goal was to use single Yagis. If one wanted to do a lot of operating in this mode it might be better to use two shorter Yagis, stacked vertically. What I find is that I just can't operate until the Moon is up to 25 or 30 degrees elevation angle. The pattern of the two Yagis could bring this angle down. This is more important for people living at the higher latitudes. One should strive for low sidelobes, for the same reason,