It may not be simple overdriving with too high a mic gain setting, Steve.
Many, if not most, soundcards output a highly distorted, clipped signal
if the mixer/audio level controls are advanced much above the 1/3 to 1/2
point. This cannot be detected unless the operator is watching either the
audio output of the card into the rig and/or the r-f envelope output of
the transmitter, preferably both.
Another source of broad signals is the introduction of 60 Hz and 120 Hz
trash into the input audio which causes the PSK31 signals to repeat at
intervals of 60 and 120 Hz above and below the actual carrier frequency.
Simply "turning down the modulation level" does not cure these problems
which 99% of PSK31 users may not know exist. The only sure way to know
what is going out on the air is scope monitoring, and even that can miss
the more subtle problems. I use two PSK stations here in the shack,
monitoring the output of one with a receiver and computer doing a
spectral estimation of the output. That is the only way that many of us
have been able to come up with that enables you to know exactly what you
are putting out.
PSK31 when in IDLE produces a textbook perfect two-tone audio signal
which in turn produces the classic two-tone output envelope signal used
for SSB rig testing, etc. An acceptable PSK31 signal will have its
third-order sidebands down at least 25-30 db and higher-order distortion
products should be at <40 db or better, just like a quality SSB signal.
The spectrum of a PSK31 idle signal is exactly like that of a
two-tone-modulated SSB transmitter.
Steve, another thought: are you sure that is a PSK31 station that you
heard? What did the waterfall display look like? There are
"Hellschreiber" stations becoming active that have MUCH wider signals
than PSK31 but which might sound like it. BTW, these stations claim CW as
their operating mode and assert their "right" to operate in CW band
segments.
72/73, George AMA 98452 R/C since 1964
Amateur Radio W5YR, in the 53rd year and it just keeps getting better!
AutoPOWER Systems, Fairview, TX (30 mi NE Dallas) Collin County
QRP-L QRP-ARCI FISTS NORCAL ZOMBIE ARS 10-X 33.2 N 96.6 W EM13RE
Steven Weber wrote:
>
> The last couple of nights I've been on 40 M and noticed a moderatly
> strong PSK-31 station comming on 7.040 Mhz.
> Wish I had a way to tell him to turn down the modulation level!
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