Hi Rich--
Sorta further to what Tom said and more specifically answering your
question with respect to the Corsair II.
When you mix (or 'beat') two frequencies together, you get four products
of the mixing: each of the original frequencies; and their sum and
their difference which are called beat frequencies. 'Zero beat' means
that one of the 'beat frequencies' is zero, which means the two original
frequencies are the same as each other.
Years ago if working AM, you could turn your vfo on and move it onto
another's carrier frequency. The difference between the two
frequencies, if within the audible range, could be heard from your
speaker. You adjusted your VFO until the pitch went down to the bottom.
Either direction you moved your VFO from there, the pitch would
increase. Right on the frequency, you could get it so close that you
could count the cycles of difference which sounded like a wah-wah-wah.
When you got it down to where the difference between the frequencies was
zero, you were said to be 'zero-beat.' With today's transceivers this
method is not possible. What 'zero-beat' means in today's parlance is
to be right on somebody else's frequency.
The Corsair II works like the other older Ten-Tecs. When you are on SSB
with your offset turned off and you have the other station tuned in to
sound right, you are on his frequency. On CW, though, it depends on the
pitch you are hearing from the other station. Ten-Tecs of that vintage
used an offset of 750 Hz, so if you have a 750 Hz tone from the other CW
station, you are right on his frequency if your own carrier oscillators
are properly aligned.
Most of us cannot tell 750 Hz from 850 Hz or 650 Hz, though. For that
reason, the Corsair II has a spot button. This removes the offset from
the receiver so that you can tune in the received signal to where either
way you tune, the pitch increases. Right in the center is the place you
want to set your rig for CW. This is easier to explain than do for me,
and only works with fairly good signals sent by someone who sends long
enough for me to do the job. Others seem to have fine success with it.
There is an alternative approach which works. A guitar pitch pipe has
the G on it, which is 746 Hz, I think. That is plenty close enough to
750 hz for government work. You can tune in the other station to where
his tone matches the G you blow on your pitch pipe and you are there.
If you want to hear something really weird sounding, tune in the signal
(without the spot button) to match the pitch pipe and you can actually
hear the beat frequency as you bring the two tones right together --
once again it is the wah-wah-wah sound.
It was suggested that you set your sidetone frequency to 750 Hz and then
tune in the signals to where they match your sidetone frequency. That
will work well in theory, but in practice with my Corsair II, I have
difficulty matching my sidetone frequency to anything. Perhaps that is
because my sidetone has a funky waveform.
Hope this helps. . .
73 de Mike N4NT@bnoc.net
-----Original Message-----
From: Rich Vizcarra <rvizcarra@LittonSolidState.com>
To: 'Tentec Reflector' <Tentec@contesting.com>
To: <tentec@contesting.com>
Date: Thursday, October 22, 1998 12:15 PM
Subject: [TenTec] Zero Beat
>Gang - This is a subject that comes up from time to time, but I have to
>confess that I have never seen an answer that clearly describes it; at
>least for me. You can respond to the list or directly to me; your
>choice. This is probably a subject that would interest others. I have
>done at least a cursory search (ten tec archives, ARRL operator's
manual
>& general internet search), but have turned up very little. If you know
>of a URL that will answer the question, that will work for me. What I
>would really like to know is what is Zero Beat in the general sense;
how
>do you achieve it from a practical point of view? What are the steps
you
>go through? More specifically, I just purchased a Corsair II; what a
>great radio. I have read through the manual but the process is still
>not clear to me. Again, what is the step by step process. This is
>pretty fundamental stuff for most of you; therefore, I apologize in
>advance. But this is my first real radio in a long time and I would
like
>to get it right. I'll probably enjoy myself a lot more if I do.
Thanks
>in advance for the help.
>
>73, Rich K6TM
>
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