From: Kevin Dawson (blfjrh.spqdzlnu@rivella.ch)
Date: Fri Jun 29 2001 - 01:18:30 EEST
> > 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.
>
> According to the datasheet I have it doesn't have any of the above. But it
> does have a 400Hz shift V.23 mode that probably can be used by scaling the
> xtal.
OK, without looking I couldn't say - it's been a few years.
Put it down to my unrefreshed dynamic memory having parity errors :-)
> > 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.
>
> You mean a HamCom type of interface? There are packet radio drivers for it
> but not on Linux (I'd guess the interrupt load would be too high (?)).
Yes.
Regarding interrupts, if you used low audio frequencies
like (say) 500 and 700Hz, that will bring the interrupt rate down.
1000/1400 interrupts per second might be manageable.
It is a compromise between that, the audio response of the radio
and the transient response of the HamCom filters.
Kevin
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