From: Niall Parker (zudpq@swps.edu.pl)
Date: Tue Jun 26 2001 - 09:23:01 EEST
On Mon, Jun 25, 2001 at 07:51:21PM -0700, Bob Nielsen wrote:
[snip]
> Thus, although you can communicate between the computer and the Baycom
> device at 300 baud, it would still communicate with the radio at 1200
> baud, although with a slower character rate (increased mark dead time).
> It would not be compatible with 300 baud HF packet operation.
Actually, the TCM3105 (and similar units) are dumb modems, bit rate in
equals bit rate out. The frequency shift is 1 kHz, so the bandwidth occupied
will be wider than the conventional HF shift of 200 kHz, but most simple
PLL based demodulators should be able to decode it OK still.
If you want to get the 200 Hz shift of a conventional HF modem, look around
for one of the older Exar based Bell 202 modems which can be retuned for
different frequencies and shifts by substituting resistors and/or a cap.
... or bypass all that and use a sound card :)
... Niall, VE7HEX
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