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

Zach Leffke zleffke at vt.edu
Fri Aug 12 15:29:32 UTC 2016

Hi Dani,

     Great questions.  On my long list of 'TO DOs' for the VTGS is to 
get our github account up and running to push our satellite GNU Radio 
work back out to the Open Source community.  Once we do I'll post the 
code along with the pyBOMBS recipes for installation.  I don't have an 
ETA for that though (maybe this Fall semester.....?).  There are a few 
other things in the Out of Tree Module that would be of use to Hams as 
well.  For example we have scramblers and descramblers that are AX.25 
compliant.  We also have an AFSK TRANSMITTER as well as an AFSK receiver 
(I've seen a few AFSK/AX.25 GNU Radio projects, but they are all 
receivers and they don't separate the demodulator from the link layer 
protocol).  Fair warning if I ever do get the code posted and you play 
with it, the output of the modem is the raw 256 byte packet (after FEC 
decode and CRC check, that I send to a PDU socket). There is no pretty 
dashboard in our code.  The intent was to develop a separate dashboard 
for AO-73 that would connect to the GNU-Radio modem over the socket (we 
operate our ground station remotely from a mini Mission Control at 
Space at VT).  That is also on the long list of to dos.

I've never compared our receiver to the funcube dashboard side-by-side 
in a real detailed way.  That is definitely something I would be 
interested in seeing the results of.  I do use a funcube dongle with the 
dashboard for student demos with an arrow antenna.  I would say 
comparing my 'impressions' of both is that they both work very well and 
basically just after AO-73 pops over the horizon we get solid decodes on 
both (FEC is great!).  My gut is that with all of the great folks at 
AMSAT-UK and all of the good engineering effort they put into that 
software, that theirs probably performs a bit better.  We make up for 
our probably higher implementation loss by have a pair of 14 element 
crossed yagis (2 M2 antennas 2MCP14s combined in phase), so lots of 
gain. The AO-73 dashboard also does the Automatic Frequency Correction, 
which is something we don't quite have implemented in our GNU Radio 
flowgraphs yet (we tune either manually or via a Gpredict interface to 
GNU-Radio to get inside the capture bandwidth of our differential bpsk 

Something that would make a good comparison easier to implement, and 
that I would like to see, is a Linux version (and open source) of the 
FunCube Dashboard.  I don't really want to mess around with Windows 
emulators on our Linux servers/workstations in the VTGS. That could be a 
fun student project to try to integrate a Linux version of the Dashboard 
with the Socket interface to GNU Radio (and would allow us to forward 
the tlm packets to the data warehouse easier).  That's one of the things 
I really like about the AO-85 dashboard is the cross-platform support.

Good questions, thanks for the interest.  I'll try to put more effort 
into elevating the github thing on the to do list this semester.

-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 10:55 AM, Daniel Estévez wrote:
> El 12/08/16 a las 16:48, Zach Leffke escribió:
>> For our
>> GNU-Radio modem, we need about 7 dB SNR (including implementation loss
>> there) for solid demodulation.
> Hi Zach,
> Is this GNU-radio AO-73 receiver available online? It would be
> interesting to take a look at. How does it compare (in terms of SNR
> performance) to the dashboard software?
> 73,
> Dani EA4GPZ.
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