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Re: AO-40 data mode




Most of these assumptions are correct but I'd argue a couple of other 
points:

1. Even if the mode needs doppler tracking, it doesn't mean we shouldn't try 
it anyway.  I'm sure with time the software can be set to keep a lock on the 
signal.  With wider bandwidth it should be easier to do this anyway.

2.  The beacon FEC'ed data will of course outperform a voice PSK signal... 
that makes sense.  But there is still potential for better quality over 
analog SSB.

3. I don't understand why you think you'd need 3dB more power?  Than what?  
SSB?  The only disadvantage to digital modes is that silent parts of speech 
still takes ones and zeros to get across, but on the other hand, the peaks 
in SSB would be higher.  Averaged out, the FEC'ed digital signal should take 
less spectrum and power than the SSB voice.  It's mathematical magic, yes, 
but true.

4. We are also not talking spread spectrum here, though it could be 
possible.  I think a standard voice bandwidth (<3KHz) modem could be made to 
work for this.  It's about time someone is interest in doing this.

Fred W0FMS

>From: Emily Clarke <emily@emilyshouse.com>
>To: "Howie" <hdefelice@petrexintl.com>, "DC" <dc@dcarr.org>,        
><amsat-bb@AMSAT.Org>
>Subject: Re: [amsat-bb] AO-40 data mode
>Date: Thu, 23 Oct 2003 11:43:33 -0700
>
>At 11:59 AM 10/23/2003 -0500, Howie wrote:
>>Good examples of ham radio applications that achieve the
>>same results are PSK31 and AO-40 telemetry with FEC.  Using BPSK or maybe
>>MSK with FEC (forward error correction) would produce many more usable 
>>QSO's
>>on AO-40 and maybe eliminate LEILA from our ears.
>
>The MB is only 400 bps so that's probably not a good example.  And it's 
>running at least 10db above QSOs.  My limited experiments with PSK31 are 
>that the bandwidth is not sufficient to allow the AFC to keep the doppler 
>under control (though I am not computer controlling my transceiver so I 
>don't know if that would make a difference.)  I'm not sure but I think 
>using an FEC corrected PSK modulation like QPSK will now introduce two 
>other problems.  The first is that you will need at least 3db more power 
>and the tuning is now more critical due to the sensitivity of the Viterbi 
>decoder.
>
>I don't know much about the response envelope of AO-40s transponder but I'm 
>assuming a spread spectrum signal wouldn't be acceptable because it will 
>raise the noise floor?
>
>- Emily
>
>
>
>
>----
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