[aprssig] Looking for 9600 baud equipment

Jack Spitznagel frawg at frawg.org
Fri Oct 3 10:40:49 EDT 2008

A "dumb" question:

Why can or can't multiple parallel tone modem systems be used? They work
pretty well on some pretty terrible paths on SSB with MFSK and OLIVIA.

We are using FMN so the inherent SSB problems are not there. Would
mobile flutter problems be offset by the advantage of staying a a slower
bit rate with higher throughput? Wouldn't one be able to ignore
pre-emphasis adjustment in a properly designed system? Most newer sound
chips can handle multi-tone pair modes very well well.

Rough example of advantage: 8 tone pairs at 1200 "8-bit characters"/sec
is theoretically 8 times faster than 1200 bits/sec. at the same
transmission rate. Could you push the speed limit with a bit rate of 4800?

Just curious.

Jack - kd4iz

Patrick Green wrote:
> Phone models spend a good 20 seconds syncing up.  Totally unsuited for
> APRS.  Not to mention you aren't going to get the best speed if there
> was any fading during the "training" process.
> 73 de Pat --- KA9SCF.
>     Not at 56k, I don't think.  I'm pretty sure 56k requires a direct
>     T-carrier connection on one end.  They should only be able to do 33.6k
>     peer-to-peer.
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