It is possible to decode, though conditions need to be just so. I was able to turn this exact phenomenon into a student project at VT for the undergrad SatCom course. The students had to simulate the event to predict when the chain (crosslink) events would occur (line of sight between the two birds and FO-29 over the VTGS), what the Link Budget looks like during the chain event (so we can predict the best opportunity for successful decodes), and what the Doppler profile would look like during the event (which tends to be really different than expected, like the center frequency drifting UP due to the relative motion between the birds). We then used the VTGS to monitor a few of the events based of the student generated schedules and two of the students got extra credit on the project because they were present during a successful demodulation (and their predictions were spot on!).
I posted a short blurb on our facebook page about it: https://www.facebook.com/vtgroundstation/
During that event we were able to dig out 6 packets using GNU Radio and a custom AO-73 modem (Basicaly Phil Karn's AO-40 reference code wraped for GNU Radio, also implemented by a student). Probably of more interest to this list though is Paul's (N8HM) success with standard equipment. He dug out 9 packets using the Funcube Dashboard and I believe the Funcube dongle.
During that particular conjunction event, one REALLY interesting thing that happened is that we caught the instant in time when AO-73 moved out of eclipse. We could see the signal drifting along just a few dB above the noise (willing it to increase just a bit to achieve sufficient SNR for a solid decode) then all of a sudden it jumped up by 10 dB and packets started decoding!
Very cool stuff. FO-29 is one of my favorite birds for looking at these types of exotic cases precisely because it's transponder covers half of the Amateur Satellite Service 2m band. As previously mentioned, lots of opportunities for interesting events (crosslinks, gelocating the FM interferers, etc.). AO-73 is also a great bird because of the Forward Error Correction on the TLM link (among other reasons). For our GNU-Radio modem, we need about 7 dB SNR (including implementation loss there) for solid demodulation.
Fine Business!
-Zach, KJ4QLP
Research Associate Ted & Karyn Hume Center for National Security & Technology Virginia Polytechnic Institute & State University Work Phone: 540-231-4174 Cell Phone: 540-808-6305
On 8/12/2016 4:16 AM, Daniel Estévez wrote:
El 12/08/16 a las 08:58, Scott escribió:
While monitoring FO-29 for activity tonight, I saw what appeared to be the distinctive waveform of the telemetry stream from FUNCube-1.
Is this common? Or even possible? It was certainly a first for me. I see that the telemetry frequency on FUNCube-1 falls inside of the uplink range for FO-29.
Hi Scott,
Certainly it's FUNCube-1 via FO-29. That's not so common, but I've seen a few reports of this before on the mailing list. Someone even managed to decode the telemetry. Probably you can google if you're interested in previous reports. Also, satellite-to-satellite QSO is also possible for some pairs of satellites and has being done (for AO-7 and FO-29 as far as I can remember). Note that the transponder of FO-29 is quite wide and will retransmit a lot of birds that downlink on 2m, so lots of possibilities for reception via FO-29.
73,
Dani.
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