> > (I heard several stations off by at least that much on the
> > Ten-Tec net today, a couple of them using Orions), which is
> > noticeable on SSB.
I guess the question is whether they had their radios set by the dial or
tuned "by ear". A lot of people have a problem tuning an SSB signal
correctly by ear, especially if they do not know the in-person voices.
My Orion was off by about 20-25 Hz at 7 Mhz. I tried adjusting it numerous
times, but it always ended up about that far off. My Orion II settles in at
around 2 Hz error at 7 Mhz, and it's consistently there after just a few
minutes warmup. Not too bad, and I don't plan to fiddle with it :-)
(That's measured with a counter on a GPS stabilized time base).
> > ...which begs another question. If you can hear that
> > you are off frequency by 20 Hz, why is ppm accuracy even
> > necessary in the first place? ;-)
But a lot of people have a hard time telling.
In Region 2 AFMARS, we used to use a thing called a FATTO -- don't recall
off hand what it stands for any more, but I still have one somewhere -- to
get net participants on the same frequency. Basically an audio oscillator
with a strong 2nd harmonic, that would be transmitted by net control
(simple, just a little speaker up to the microphone). When you listen to the
thing on SSB it's VERY easy to tune and VERY obvious when you are on the
same frequency as net control because the audible beats between the
fundamental and 2nd harmonic would disappear. Without a technique like
that, stations were all over the map, so to speak, and not just the guys
using KWM-2's or other analog radios. You can use the same technique on a
voice signal, too, but it can be hard to hear the beats go away in the
on-frequency sweet spot when you have a typically restricted audio bandpass.
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