On Mon, Sep 19, 2011 at 12:52, Kok Chen <chen@mac.com> wrote:
> If the modem that is optimized for 45.45 baud does not change the internal
> filter for 75 baud operation, the SNR does not go up. However, something
> even worse happens since a 75 baud signal will cause some pretty severe
> inter-symbol interference (a signal QRM'ing itself, so to speak :-). You can
> even see this effect when using 45.45 baud, if you use a crystal filter in a
> rig that is too narrow, without also having an appropriate shape for binary
> 45.45 baud data.
>
I wondered about this when I was trying to copy K9MUG/4. All I did
was set MMTTY to "decode" 45.45 bauds. I didn't fiddle with any of
the other 10,000 settings on the config screen (for fear I'd delete
half the internet if I did).
I'm guessing that what I really need is a 75-baud "profile" in MMTTY
that optimizes things for that speed (along the lines of 23-Hz shift
profile that's distributed with the software).
Anyone done that that is willing to share?
--
Peter Laws | N5UWY | plaws plaws net | Travel by Train!
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