From: Kevin Dawson (vhfiv.zsgapst@magnitec.fi)
Date: Thu Jun 28 2001 - 05:00:32 EEST
> [snip]
>
> 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.
The TCM3105 has a variety of modes, selected by various connections of 3 pins
(TXR1, TXR2 and TRS - sorry, I don't have the data handy to say how).
Standard 200Hz shift modes like V.21 and Bell 103 are available.
> 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.
It would be easier to make the 3105 work...
> ... or bypass all that and use a sound card :)
Another method would be to use one of the converters that SSTV uses -
the type that filters a square wave from the ttyS and squares up
the received signal back to it.
The computer does the FM part.
I don't know if anyone has ever written a packet driver for that,
but a good place to look would be in SSTV software.
Kevin
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