Listening for the CAS-5A Chinese satellite at 435 MHz – 15th Dec 2022


CAS-5A is a Chinese amateur radio satellite which was launched from the Yellow Sea off China on the 9th of December 2022. It’s an unusual satellite in that it has transponders with an downlink in the 70cms band and uplinks on the 2m VHF band and the 15m HF band.

Today on the 15th of December 2022, I did a quick test to see if I could hear it. The pass was from 15:18 to 15:30 UTC with the satellite reaching a maximum elevation of 44 degrees above the horizon. 

The satellite has a CW beacon on 435.570 MHz so I left my radio listening on that frequency on USB. My antenna was a very modest home made colinear vertical antenna in the attic of my house.

My primary objective was to catch the doppler shift of the beacon and my secondary objective was to listen for any activity in the transponder passband.

The image on the left shows the audio spectrum of the received audio from my radio. The trace showing the drifting CW beacon can be clearly seen. In the space of just 15 or so seconds, the CW signal had moved downwards about 1KHz in frequency due to doppler shift. 

As you might imagine, this make manual tuning of a CW or SSB  signal on the 70cms band quite a challenge and confirms the need for some sort of CAT software to control the frequency of the radio to compensate for the doppler.

The signal of the CW beacon was also quite weak and was just above the noise. I’m sure that a pass overhead would probably be stronger but the beacon is still only 100mW to a whip antenna. The test confirmed to me that a small crossed Yagi antenna would probably be much better.

As for activity on the satellite, I did tune upwards after the beacon test and I could hear the weak warble of a FM signal on SSB but it was too weak to hear on FM mode.

The CAS-5A satellite has been given the AMSAT name of FO-118. A users manual for the satellite can be viewed HERE


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