[amsat-bb] Fo29 retransmitting AO73 Data !

[Zach Leffke]

YES!  very fun project.  I caught the same pass Paul is referring to, we 
only got 7 frames :-( here at VT.  The fun (and proud) part for me was 
it was all part of a undergraduate class project for the satellite 
communications course where the students had to simulate the orbits 
(using STK), predict pass windows where the crosslink was possible (line 
of sight from AO73 to FO-29 and LOS from FO-29 to VTGS), then for each 
pass window do a link budget computation for each 1 second timestep of 
the established chain event, and do a doppler curve estimation.

The proud part was that two of my students (undergrads) were dead on 
with their predictions, and were present during the decoding event and 
therefore got a half letter grade bump on their project grade since we 
successfully demodulated packets based on their simulations and 
predictions (not only did they pick a good window with a higher chance 
of success, their doppler curve matched nearly perfectly, allowing us to 
tune correctly to decode the packets).

The magic part that folks should keep an eye out for is trying to make 
the attempt when AO-73 is in sunlight since you get a 10 dB bump in 
output power from AO-73 in the beacon.  That was also a great teaching 
moment during the attempt where we could see the signal drifting (up in 
frequency since AO73 and FO29 were closing on each other, not down like 
you might expect with normal doppler) in the spectrum display, but 
barely breaking the noise floor, then all of a sudden there is this 10 
dB jump in SNR (AO-73 coming out of shadow and into sunlight) and 
packets start decoding!


very fun project, very hands on for the students.  Do some research, 
develop a simulation, synthesize something meaningful about the real 
world from the simulation, try it in the real world, and then explain 
what worked and what didn't and why, but with actual satellites in orbit!

Also, they used the free version of STK in the class project and then 
wrote scripts in python to process CSV data generated by STK, so all of 
this is simulation stuff is doable by hams with completely free software 
and tools.

One of my all time favorite student projects......brought to you by the 
fabulous folks at AMSAT, in this case our japanese (FO29) and english 
(AO73) brethren!

-Zach

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 2/10/2017 9:10 AM, Paul Stoetzer wrote:
> Now you have to try decoding it! I got 9 frames of data from a
> recording of AO-73 via FO-29 once.
>
> 73,
>
> Paul, N8HM
>
> On Fri, Feb 10, 2017 at 9:07 AM, jeffory broughton
> <jefforybroughton at gmail.com> wrote:
>> It was very interesting and exciting at 13:58 utc this morning to hear A073
>> data coming over Fo29 .Both birds were over Quebec Canada at the time, A073
>> was transmitting on 145.937 , Fo29 was receiving  and retransmitting it on
>> 435.863 mhz.It only lasted a minute or so.I have only heard this one other
>> time.
>>
>> jeff broughton WB8RJY
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