On 11/07/2017 19:12, Tim Carlson wrote:
Would you consider that the first signal on the left is being
overdriven somewhat? Or is that just a consequence of a stronger
signal? Or is it some atmospheric condition causing the signal to spread?
Hi Tim,
hard to tell but it is all too common for the Tx audio level fed to the
rig to be too high. This causes non-linearity and will almost certainly
widen the transmitted signal. The main product of clipping is harmonics
but if the sender is using the split operating facility that is largely
innocuous due to the harmonics being above 3000 Hz and attenuated by the
rig's Tx SSB filter low pass cut off. Still there is no excuse for over
driving the audio input to the rig and there is a secondary consequence.
At each frequency shift of the modulation there is a minimal phase
discontinuity, we shift the phase without a glitch but nevertheless it
is a discontinuity. These small discontinuities fractionally widen the
signal when the audio is correctly matched through to the transmitter
but over drive widens them considerably. This is what you are seeing, a
horizontal spike on the waterfall at each tone shift.
You must also be careful about attributing blame in these situations,
all of the above can happen on the receiving side too, so check your own
house is in order before accusing another of having a poor signal.
73
Bill
G4WJS.
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