[DSP-10] SSB Transmit distortion

[Bob Larkin]

Relative to recent reports, I recently made tests trying to find a 
distortion problem in SSB using the DSPx/KDSP10 hardware. I found no 
problem, old software or new.  Reports from K7NQ, using the same hardware 
(and software) were the same.

If anyone has a problem in this area, please let me know.

As a refresher, the transmit audio goes through the equalizer and then has 
a clipper/filter.  A few dB of clipping are generally beneficial for DX 
copy, and do not cause splatter because of the filtering following the 
clipper.  The maximum amount of clipping possible is 12 dB, after which the 
output of the filter will have distortion.  This latter condition is easy 
to avoid, and should be!

To tell how much clipping is applied, watch the S-Meter bars during 
transmit. At that time, they correspond to 1 dB of peak clipping per bar. 
Avoid generally going past about 6 bars, by adjusting the microphone gain. 
A final check is to watch the ADC and DAC bar graphs on the bottom line 
(SCRL-F3). The critical item is the DAC bar graph. The big, red, overload 
bar should not come on.This means the 16 bit range has been exceeded, and 
splatter will result.  I won't try to put the use and setup information 
here, but look at the User's Manual
http://members.ispwest.com/kd7ts/ver3/1ChOne.html#SSB_OPERATION

This process is identical for the EZ-Kit and the DSPx.

73,
Bob  W7PUA