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Re: D700 TNC Calibrate Mode



Ok great, the tap bit on the scrambler is 12.  Good.
Now, I read in the TAPR documentation that it impliments NRZI not NRZ. 
Is this the case?
~Danny

-----Original Message-----
From: "Howard Long" <howard@howardlong.com>
Sent 6/5/2006 8:18:41 AM
To: "'Danny Jacobs'" <jacobs@physics.montana.edu>, amsat-bb@amsat.org
Subject: RE: [amsat-bb] Re: [amsat-bb] D700 TNC Calibrate mode etc (II)

Hi Danny

I know some of your questions have already been answered, I just have a
little more to add here.

The document http://www.jrmiller.demon.co.uk/products/figs/man9k6.pdf is the
one we used as the definitive one on SSETI Express. This gives a deviation
of +/-3kHz and a 15kHz IF bandwidth for 9600bps. I spent many, many hours in
front of a scope/counter/siggen doing BER tests with a bunch of 9600 (and
38400bps) modems about 18 months ago, including (but not limited to!) the
SYMEK TNC-3S, and Paccomm TNC-NB96, the Paccomm Spirit-2, the LL Grace
DSP-12, the TNC7multi and the modems integrated into the Kenwood TH-D7, the
TMD700 and TS-2000.

The scrambling polynomial 1 + x^12 + x^17 LFSR is correct here:
http://www.amsat.org/amsat/articles/g3ruh/109/fig03.gif. John KD2BD's
schematics here
http://www.amsat.org/amsat/articles/kd2bd/9k6modem/schematics.html are
correct.

There will be an increase in bit error rate if the filtering between Tx and
Rx aren't matched.

If pushed for the most commonly _used_ 9600bps design, I would hazard a
guess at the G3RUH design that was copied commercially on many designs.
However, probably the most commonly _available_ (as opposed to the most
used!) will almost certainly be the Tasco modem chip sets in the Kenwood
TH-D7, TM-D700, and TS-2000 radios. More recently, DSP based 9600 modems
have also become available.

There are notionally positive benefits in the implementation of the KD2BD
modem over the original G3RUH and K9NG modems noted in particular here
http://www.amsat.org/amsat/articles/kd2bd/9k6modem/ although I've not seen
any studies indicating the extent to which BER is improved.

73, Howard G6LVB
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