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RE: AO-40 data mode... APRS???



This brings up a good point...  Is anyone doing APRS on AO-40?  If not, is
there a problem with doing that?



-----Original Message-----
From: owner-AMSAT-BB@AMSAT.Org [mailto:owner-AMSAT-BB@AMSAT.Org]On
Behalf Of DC
Sent: Thursday, October 23, 2003 10:39 AM
To: amsat-bb@AMSAT.Org
Subject: [amsat-bb] AO-40 data mode


As I was listening to AO-40 the other day I wondered if it would be
feasable to send voice as highly compressed data in order to achieve
better S/N than with SSB phone.  Based on my experiments thus far
3500bps (bits per second) is the lowest bit rate I've been able to
achieve.  This limit is not a quality limit but its the lowest that I
force the reference speex codec to go.  At this rate quality is similar
to that of conventional telephone.  This rate is utilizing a 8khz audio
bandwidth but the speex library features a 4.8khz bandwidth option that
should drop the rate even lower.  My ultimate goal is to have better
quality speech than SSB for a given S/N ratio with 1200bits per second.

My question is what data modes are allowed on AO-40?  Also as this is my
first real step into radio data transmission what modulation schemes
should I look into.  My priorities for a modulation scheme are best
minimum S/N requirements, smallest bandwidth, and not so important
standardized.  Having the coding be an established standard isn't all
that important because my audio compression (speex) while open source
certainly isn't standard either.  What kind of bandwith am I going to
need for 1200bps or 3500bps?  Thanks for your input,
-David Carr
KD5QGR

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