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Re: AO-40 data mode



> The MB is only 400 bps so that's probably not a good example....

The example was to compare how much better telemtry with FEC performs
compared to telemtry without FEC

>  My limited experiments with PSK31 are  that the bandwidth is not
sufficient to allow the >AFC to keep the doppler  under control...

This is is a limitation of the AFC algorithm in some PSK31 versions, I
believe there is a version around tweaked for satellite use. Again, the
illustration was the advantage of PSK modulation with FEC vs conventional
RTTY.

> 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.

This is mixing apples and oranges. FEC can be applied to any modulation
technique and is a baseband function. The whole purpose of FEC is to reduce
the amount of power required by obtaining a higher BER for a given C/N by
correcting individual bit errors post demodulation.

> 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?

This could be an option but I know there are readers of this list that are
better qualified than me to comment.

Howie AB2S

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