Don,
Zero beating does not involve hearing down to zero cycles. It is matching
two tones, whatever their frequency, until; the beating phenomenon, which is
not a sound comprised of frequencies lower than the audio passband of the
receiver or below the lower limit of human hearing, stops. As you know, it
is more of a whooping sound. It is clearly within the audio passband of
most radios. I used to use my K2 listening to WWV with Spectrogram as a
frequency reference.
I recently built two NorCal FCC1/2 DDS VFO's. If I had used the
K2/Spectrogram to calibrate them, they would have been accurate to within a
few Hz, as you say. By using my Japan Radio listening to WWV in AM mode (no
Spectrogram needed!), it was easy to hear the VFO beating against WWV's
carrier. Without being zero beat, it is possible to count the beats per
seconds if you know how to tune a piano. You can tell how may cycles it's
off. But anyone can easily hear when the beating process stops, and then
the *maximum* error the VFO readout displays is 1 Hz. I have found it very
hard to get this kind of accuracy using Spectrogram.
Regards,
Andy W9NJY
K2 KX1
---------------------------------------------------------------
Message: 16
Date: Thu, 1 Mar 2007 20:54:29 -0500
From: "Don Wilhelm" <[EMAIL PROTECTED]>
Subject: RE: [Elecraft] Frequency counters for Alignment
To: "Ken Kopp" <[EMAIL PROTECTED]>, "Ron D'Eau Claire"
<[EMAIL PROTECTED]>, "'Elecraft Discussion List'"
<elecraft@mailman.qth.net>
Message-ID: <[EMAIL PROTECTED]>
Content-Type: text/plain; charset="iso-8859-1"
Ken and all,
What you say is true - but you can detect the transmitted tones sent by WWV
with great accuracy. See http://tf.nist.gov/stations/iform.html#stdf for
innformation about what tones are transmitted at what times.
With the audio of a SSB receiver fed into the computer soundcard, and the
computer running a program like Spectrogram, one can align the received
tones with properly set Spectrogram markers and when the transmitted tones
line up with the received tones, you can be certain that WWV is tuned
precisely. This is actually more accurate than trying to listen for the
carrier at zero frequency - neither the receiver audio nor the human ear can
respond to zero frequency, and attempt to do so may be off by +/-30 Hz or
more - detecting the tones with a graphic display will allow you to tune
within a few Hz.
73,
Don W3FPR
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