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[aprssig] Looking for 9600 baud equipment

Scott Miller scott at opentrac.org
Tue Sep 30 03:00:35 UTC 2008


> 	I still think we need something MUCH faster than 1200 or 9600 -- 56k 
> ought to be a cinch, since we can buy telephone modems to do it, but of 
> course we'd need to go to a much higher frequency band as well.

You can do a lot on the 440 band - if you want to cough up EUR €1250 for 
  a TRX4S.  I'm hoping I can come up with a cheaper option for at least 
19.2k - shouldn't be that big a step up in bandwidth.

As for telephone modems, they have the advantage of much quieter channels.

In reading through G3RUH's original documentation on his modem, I got to 
wondering if it'd be feasible to add an automatic equalization feature 
for high speed links.  The G3RUH modem could be loaded with filter 
coefficients to match the exact transmitter and receiver being used, to 
compensate for the channel as a whole.  It'd be impractical for APRS, 
but for connected mode, you could exchange a quick series of tones like 
landline modems do and automatically adapt.  It wouldn't directly 
increase the speed, but it'd improve your S/N ratio.  Has anyone done 
that in the ham world?

Scott
N1VG





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