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  Topic: RTTY, SSTV & audio shaping (0 replies)
#1     Thu Dec 07, 2006 4:38 pm
VK1AC
Bywong, NSW Australia
 
Join Date: Oct 2006
Posts: 4
Subject: RTTY, SSTV & audio shaping

Hi all,

Another quirk we found about sending digital modes on CQ100 is the audio
shaping that goes on in the codecs. We've now had brilliant success with
RTTY just by changing the Mark tones down to 1000Hz.

It looks like CQ100 has a sloped cutoff around 2100-2300Hz that plays
havoc with regular RTTY. (watch the spectrum display on MMSSTV & you'll see the cutoff)

Changing the tone frequency a bit lower gets you right onto the codec 'sweet spot'.

The PSK guys don't see it as much (error correction) but I'd say it
causes a bit of picture degrading & sync loss on SSTV too. Of course, the occassional dropout doesn't help either ;-)

Cheers,

Alex VK1AC
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