karn@eagle.UUCP (Phil Karn) (10/01/83)
The Oscar-10 mode L transponder (1269 up, 436 down) was turned on for the first time a week ago with disappointing results. The downlink was excellent, with steady non-fading signals, but the uplink receiver performance was more than 20 db worse than expected. While the spacecraft beacons were of excellent quality, very few stations could get enough power into the satellite to rise above the noise level; the strongest was only 6db above the noise. A theory was constructed having to do with the relay that switches the receiver between the high and low gain antennas. Since the first test, this relay was toggled a number of times under ground command. The second mode L test was conducted this week and the following bulletin was later loaded into the onboard computer: M FROM DJ4ZC, 28.9.83: THE MULTIPLE SWITCHING OF THE 24 CM ANTENNA RELAY RESULTED IN A 10 - 20 DB IMPROVEMENT OF MODE L PERFORMANCE. NOW PERFORMANCE IS ABOUT 10 DB BELOW NOMINAL AND A NUMBER OF STATIONS HAD VERY GOOD SIGNALS. THE MODE L RX ON THE OMNI RESULTED IN A 12 DB LEVEL REDUCTION. CONCLUSION: WE HAVE AN ANTENNA RELAY PROBLEM. FOR SSB QSO'S AN EIRP OF 40 DBW OR MORE IS SUGGESTED. OVER THE WEEKEND ATTITUDE WILL BE CORRECTED AND THEREAFTER CONTINOUS MODE B (EXCEPT L-DAY) IS PLANNED. KARL The guess that the relay was at fault is apparently correct, and I'd suspect that some further toggling of the relay should help things further. The advantage of the mode L transponder will be that it has a wider bandwidth (800 khz vs 150 for mode B), better antennas since the 70cm and 23cm high gain antennas were apparently uninvolved in the launcher collision, and better downlink performance since the cosmic noise background is much lower on 70cm than on 2m. 73, Phil Karn, KA9Q