[RTTY] AFSK Splatter

[Duane Budd]

Kok Chen wrote:

"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"

One problem with the IMD readings is that the reception gain settings affect
the readings as well as the appearance of the waterfall. I do not know if
that is true with the separate meter.

I use a PTC-IIe for the little contesting efforts I make (at age 74, my
attention span is too short for serious efforts!). <grin> It does not offer
FSK, which I have always preferred to AFSK, coming from the era of the early
days of AMTOR and PACtor, when it was easy to find splatter from those using
AFSK. We were not too slow to point this out, in those days! Hi

73...

Duane Budd, W5BEN
dcbudd at charter.net