Re: [amsat-bb] AO-40 FEC

[Phil Karn <karn@xxxxxxxx>]

David Giles wrote:
> Hello all,
> 
> Just tried Phil's ao-40 FEC telemetry software - I'm impressed.
> Copied good blocks down to MA of 249 and a squint of 120 degrees.
> It didn't even raise much of a sweat - the reed-solomon code
> wasn't used, the viterbi decoder did the job.  
> I'll have to try it with a smaller antenna next time.

James G3RUH is reporting good FEC results from apogee with just a 
1/4-wave GROUND PLANE receive antenna. So your 4-foot dish is enormous 
overkill. Harder to point, too. :-)

I'm beginning to think about a modified form of my FEC format that would 
be useful for communications through the transponder. Because I'm not 
constrained by the existing spacecraft beacon hardware, I have the 
option of using a different modulation format. I'm thinking of BPSK with 
a residual carrier, a NRZ channel format (i.e., no differential 
Manchester coding) and possibly a higher symbol and/or data rate. This 
should make text chatting through the satellite possible with very small 
antennas.

Phil

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