[amsat-bb] FUNCube-1 (AO-73) Telemetry via FO-29??

Zach Leffke zleffke at vt.edu
Fri Aug 12 14:48:03 UTC 2016

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: 

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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