> In the recent discussion of allocations and band
segmentation, someone
> seemed to be suggesting that PSK31 was a broadband mode.
When I look at
> signals on my PSK31 software, they seem rather narrow
band -- typically
> under 100 Hz -- unless the transmitter audio stage is
being overdriven
> to produce IMD and HD, in which case the signals can
easily get 1 kHz
> wide. Am I missing something?
Jim,
The problem is multiple, all rooted in the fact the PSK tone
is fed into a low level audio port.
First, there often are ground loops that cause LF hum and
noise on the signal. While low level, these noises can
bother weak DX stations.
Second, if the radio has harmonic distortion it generates a
new tone a multiple of the PSK audio injection tone. Say you
run a 600Hz tone, multiples at 1200,1800, 2400 and 3000 can
get through the SSB filter with minimal attenuation.
Third, some rigs have SSB defects like carrier and opposite
sideband leakage.
(This really isn't any different than the problems Collins
faced when they generated CW via an audio tone injection in
the early 32S transmitters. It was common to hear the
Collins rigs on multiple frequencies.)
It's also quite possible receiving stations are unaware of
these issues, because they can fall outside where you
normally look on a waterfall and don't show on an IM
display. I'd say about 25% of the PSK stations I hear have
some evidence of one or more of these problems. While they
won't often disrupt strong signals, they are harmful to weak
signals.
73 Tom
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