ARISSat-1 Linear Transponder

The satellite ARISSat-1, launched from the International Space Station in July of 2011, is now literally in it's final days. Predictions are that it will de-orbit (aka burn up) around January 4th, just four days from now.



The satellite carries a linear transponder, capable of relaying uplink signals in the 70cm band to a downlink in the 2m band. Since the 70cm antenna on ARISSat-1 is missing, signals through the transponder aren't the greatest, and not many hams use this for two-way QSO's. I've called CQ occasionally for months now on the satellite, to only hear my own downlink and no one else in the passband. Fortunately, I was able to make a few QSOs in the last few weeks -- one SSB QSO with AI7W on 12/22/2011, and a CW QSO just yesterday with N6EV on 1/1/2012. It certainly is exciting to hear others on the satellite!!

Here are some screenshots from the last pass -- 1/1/2012 1848 UTC. The first shows SatPC32 and the footprint of the satellite as it approaches:


And the next screenshot shows a spectrogram of the downlink at 145.932 MHz. The white lines are my CQ calls in CW. They slope to the right due to the doppler shift of the satellite; as I transmit my uplink frequency stays fixed. You can even see how the slope of the traces gets steeper as time goes on (top of spectrogram is more recent), showing how the doppler shift gets even more significant as the satellite gets closer:


I called CQ in CW and SSB during the pass, and heard a faint SSB reply but couldn't make out the callsign and complete the QSO -- after the pass, however, I listened to my recording and could clearly hear KO6TH in CM98 calling me back! Near the end of the pass, I also heard someone tuning up in CW but signals faded out for me at that point.

Here's the location of ARISSat-1 as I lost the signal:


And the traces of my CW signal (still calling CQ at this point) as the satellite gets out of range: