RE: [amsat-bb] Re: Discovery Project: Which Mission Next?

["Howie DeFelice" <hdefelice@xxxxxxxxxxxxxx>]

I have been involved with several systems using digital voice over 
commercial geo Ku satellites in a P.T.T. network. It took a little getting 
used to, but it was not objectionable.  The commercial satellite modems 
used QPSK modulation with 1/2 rate sequencial FEC encoding at 32 Kbps. In 
retrospect, we would have been better off using Viterbi encoding. The modem 
lock time was under 100 milliseconds. If we wanted to make it faster, and 
we had the power budget (which we didn't) we could have removed the FEC 
entirely.  It has been my experience that typical layer 2 protocols like 
HDLC sync just fine over satellite circuits. I have also found that typical 
TCP/IP sessions work transparently at data rates under around 120 Kbps. At 
higher data rates, the protocol starts reducing the thru-put and other 
things need to be done.

I'm not sure if that was the kind of info you were looking for.....

Howie
AB2S

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