Working Saudisat 1C or SO-50

Working Saudisat 1C or SO-50

Last time I had posted about my partial success on accessing Saudisat 1C or SO-50, also known as Saudi-OSCAR 50. That was using my CP22E VHF antenna, which is a vertical omnidirectional antenna. After that I had homebrewed a Moxon Yagi with a Moxon rectangle for VHF which couples passively with five UHF Yagi elements. I had reasonable success on using that antenna for my other LEO satellite contacts, especially the voice transponder on International Space Station. Now I am using both CP22E antenna and Moxon Yagi for LEO satellite contacts depending on the direction of pass of satellites. As the Moxon Yagi has been kept at a low elevation and on a fixed azimuth, I will use it only when the pass is favourable for the position. At other times I still use the vertical omnidirectional antenna with reasonable results as before.

So far I have been able to complete three two way contacts on Saudisat 1C. First two were on the vertical antenna itself. Today I had to use both antennas during a single pass of the satellite. To start with, I started listening using the vertical antenna as it was a 40 degree maximum elevation Western pass, which usuallly go well with my vertical antenna. Audio from the satellite seemed to be feebler than yesterday and barely intelligible. Not sure whether it was because it was a pass during darkness causing satellite to be less illuminated and having weaker battery status. Others in our LEO Satellite Repeater contact group also felt that today the satellite audio was much weaker than yesterday. Anyway, midway during the pass I thought of switching to the Moxon Yagi as the Argentinian Amsat live tracking showed the the satellite has reached a location favourable for the position of the fixed directional antenna. Immediately I could hear a station and had a successful two way contact. It was a bit difficult to quickly unscrew one antenna and connect another during the pass. I wished that if I had an antenna switch, I could have done the job faster. But I am not sure of how much loss it would introduce for a weak satellite signal!

Incidentally Saudisat 1C was launched in December 2002 and is nearly completing 21 years of operation. Its receive antenna is a quarter wave vertical antenna in the top corner of the satellite. The satellite radio had a nominal output of 250 mW on UHF. Downlink antenna is another quarter wave vertical antenna mounted at the bottom corner with 45 degrees inward tilt. The satellite weighs 10 Kg and is orbiting at an altitude higher than that of International Space Station, with perigee of around 600 km and apogee of around 700 km. It is being operated by the King Abdul Aziz University for Science & Technology, Kingdom of Saudi Arabia. An important challenge for us is that SO-50 has to be activated first with a CTCSS tone of 74.4 Hz for two seconds to start a 10 min timer. After that uplink is on 145.850 MHz with 67 Hz CTCSS tone and downlink on 436.795 MHz, of course with Doppler correction as the satellite moves across the sky from horizon to horizon. Usually one of the operators with an excellent setup does the activation for us and rest of us can access the satellite like any other FM satellite.