On 6/26/2022 1:32 PM, Andy Durbin wrote:
I have operated WSJT-X modes for many years HF-6 meters. I'm in a very large
metro area with lots of active FT-8 users. I have learned that stations with
perfect signals on the HF bands can show all sort of artifacts on 6 meters.
For many of these stations it is not because the signals are not clean. The
various multiple signals can be caused by multi-path propagation sometimes with
associated Doppler shift. I'm not only in a signal dense area but under a busy
airport arrival route.
Yes, we see a lot of this in NorCal.
The most common FT-8 signal defect is the presence of audio harmonics
(harmonics of the tone modulation frequency). These are usually caused by
driving one or more audio stages into non-linearity and by refusing to use
WSJT-X split mode. These signal look very different from 6 meter multi-path.
Yes, and RECEIVE trash can be generated in our stations that can LOOK
like dirty signals from others. The good thing out here is that
population density, at least on 6M, isn't so great that we don't know or
at least are able to contact other users when we or they have a problem.
Last season, N5KO and I cooperated to diagnose a distortion problem in a
friend's station. Trey was at the friend's station, I monitored his
signal while they tried things.
73, Jim K9YC
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