[RTTY] DXP38 vs Soundcard stuff

Kok Chen chen at mac.com
Fri Mar 12 18:31:39 EST 2004

On Mar 12, 2004, at 5:41 PM, Phil Duff NA4M wrote:

> Can we just rely on the software's built in input "overload" 
> indicators if they have such?  Should we adjust the audio input to the 
> point just below the "overload" indication?   If not where?

Somewhere in the paperwork, there should be a spec of the peak level 
(either voltage, dbV or VU units) that the A/D converter saturates at.

But it is probably easiest to just find a software "oscilloscope" or 
"spectrum analyser" application for your machine and look at the rig's 
output through the same "sound card.".

If you want to copy both loud and weak signals that are in the same AF 
passband, then the total signal cannot be allowed to clip, or you will 
find it hard to decode that weaker signal.  This is especially true for 
the PSK ops who like to watch more than one signal in a wide passband.

If you are only interested in the case where there is a single weak 
signal in the passband below the AGC threshold of the rig, then 
adjusting so that that weak signal almost clips the converter should 
make copy easier.

In either case, more bits in the A/D converter helps.  In the latter 
case, you won't have to ride the gain that often, and in the former 
case you can copy signals with a larger range of signal strengths.  
And, of course for the case where the QSB is very deep.

Chen, W7AY

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