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[email protected] · August 20th 10, 06:36 PM posted to rec.radio.amateur.digital.misc

Bert Hyman wrote:
In wrote:

Bert Hyman wrote:
I've picked up a handful of programs for various digital modes and
driving my PC's soundcard with the line-out audio from my TenTec Omni
7 have no problem copying signals once I figure out what mode they
are.

However, all these programs have either AFC or some other way of
decoding a signal pretty much independent of what frequencies the
tones are on, so long as they're inside the passband, so it doesn't
matter a whole lot what frequency my receiver's tuned to.

On the other hand, I'm sure that if I ever get around to lashing
things up so that I could transmit, things wouldn't be so forgiving.

I haven't yet done any real research into digital modes; is there a
good (preferably online) resource, particularly something that would
tell me what the correct audio offset from the carrier is for the
various modes?

The only "correct" audio offset is to keep it inside the band.

Most programs have a panoramic window, which if set up properly, will
show your actual receive frequency with audio offset and your transmit
frequency.

I was thinking of the case where I've tuned another station and getting
good print locally and then want to reply.

I'm using a transceiver in with the transmit & receive VFOs tuned to the
same frequency.

Since the software will have grabbed and decoded his signal more or less
automatically so long as I was tuned somewhere close. When transmitting,
the software will presumably generate tones of some fixed frequency,
completely ignorant of how I've tuned the receiver. There's no reason to
think that if I transmit on whatever frequency my receiver happens to be
sitting on that I'll be anywhere near where the other guy might be
listening.

So, what's the trick to tuning digital signals so that I'm transmitting
on the "right" frequency?

Or am I over analyzing this?

Yes, with any decent software you are.

Of all the signals in the receive passband, you need to select one to deal
with.

When you do that, every program I've seen so far sets the transmit audio
offset, i.e. the effective transmit frequency, to the received audio
offset.

Assuming of course that both xmit and rcv VFO's are on the same frequency.

--
Jim Pennino

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