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RE: RE: 38k4 Operation with FT 847

Hi Mark

> Did you run similar tests with the PCR-1000?

I did run some tests with a PCR-1000 but not under the same conditions, and
I now know that those tests were badly flawed: the test was more subjective
than objective, counting the number of dumped packets on an FT-847/IFD
compared with the PCR-1000. The PCR-1000 was slightly better by a dB or so
compared to the FT-847. But I must reiterate that these were _not_ proper
quantitative tests, so take this with a large pinch of salt!

Sadly my one and only PCR-1000 is now sitting at ESA's ESTEC facility in the
Netherlands as part of the test groundstation so I don't have access to
re-run definitive tests.

In addition, what has not yet been quantified in my tests at 38k4 are the
characteristics of the tranmit side, including the exciter and the TNC's FIR
and analog filtering. Of course, once in space there's not a lot you can do
to change this, but if the transmit side can be characterised, it is
possible to correct for this on the ground receiver with DSP techniques.
Sadly, each transmitter will have differing characteristics...

I have, however, performed a number of transmit BER tests at 9600, altering
the FIR filtering. This can make a marked difference, although the combined
effects of using a low noise front end and narrower filters made the biggest
effect, empirically improving my link figures by over 10dB in some cases.

73, Howard G6LVB
Sent via amsat-bb@amsat.org. Opinions expressed are those of the author.
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