[RTTY] AFSK splatter

[Kok Chen]

On Oct 22, 2005, at 10:30 AM, robert wrote:
> I believe it's because the soundcard is making
> the sound using square wave, which is as we know a sum of a lot of  
> other
> frequency's. where are all those harmonics of those freq.

Hi Robert,

(I have changed the Subject line so poor Charles can get a reprieve :-).

I agree with you that clipped waveforms is a potential source of  
problem.

Furthermore, depending on where the clipping happens, the ALC could  
be showing no reading and yet the transmitted signal can still be  
splattering all over.

However, I don't think that sound cards, per se, are the problem.   
"Sound cards" (D/A converter) produces quantized waveforms, but the  
output from even a 8- or 10-bit Sound card is cleaner than the best  
adjusted SSB transmitter. I think  that it is more likely for the  
source of the problem to be in some other stage.

The PSK31 world often pass IMD readings to one another to help keep  
their sub band clean.  And there is even a standalone PSK31 IMD meter  
that is sold (I believe both in kit form and ready built), so you can  
make your own measurements.

Unlike the RTTY world, if you are splattering in PSK31, it won't be  
too long before someone reports back to you on the air.
I think us gentlemen and gentleladies of RTTY are just too polite?

One thing that AFSK users can do is to make their adjustments in  
PSK31, and then switch to RTTY using precisely the same rig settings  
and audio levels.  It is not that PSK31 ops are not polite, but most  
of their programs are better set up to give (relative) quantitative  
measurements.

73
Chen, W7AY