Golden Jubilee of the Oldest Operating Amateur Radio Satellite!

 Last year I had posted that AMSAT-OSCAR 7 (AO 7) was nearing its Golden Jubilee. AO-7 has completed 50 years of operation as an amateur radio satellite on 15th November 2024, having been launched in 1974, three years earlier than Voyager spacecrafts which are now travelling in interstellar space. Initially it was expected to function for just three years! In fact I read that battery failure had caused it to become non-functional in 1981. But luckily, the shorted batteries became open circuit in 2002 so that it could work on solar panels. It had two transponders, A and B, of which transponder A had uplink on VHF and downlink on 10m. It was a non-inverting linear transponder. A few reports of telemetry being still active on transponder A are there on AMSAT Live OSCAR Satellite Status Page. At the same time, there are plenty of reports of both uplink and downlink being active for transponder B.


Transponder B is a U/V transponder with uplink on 432.125 - 432.175 MHz SSB/CW and is an inverting transponder. Inverting transponder is one which inverts the sideband received on uplink, on downlink say LSB to USB. Downlink of Transponder B is on 145.975 – 145.925 MHz SSB and CW. As it was designed before the satellite subband of 435-438 MHz was implemented, operation in the United States is permitted under a waiver from FCC. Beacon of transponder B is on 145.9775 MHz CW. 

Another important life saving mission of AO-7 was investigating the possibility of locating downed aircraft and disabled vessels at sea by using Doppler analysis of signal from emergency location transmitters on those vehicles. The emergency location transmitters would send position indicating radio beacons which could be received by AO-7 and transponded, enhancing the rescue potential. Beacon uplink signal could be Doppler tracked to find the source location immediately. This information was highly useful in an era when Global Positioning System was yet to be invented! This method initially tested out using AO-7 was later implemented on a large scale and could save several lives in numerous rescue missions involving downed aircraft and ships at sea.

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