[NCARC] Tune that VFO!

[John at]

This long winded description of the method I use to tune VFO reference for
my radio gear is really super quick and easy and does not require test gear
other than 2 radios and can easily get you within a half hertz of dead on.
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Ever notice that when 2 adjacent keys on a piano or other keyboard
instrument are struck simultaneously that there is a discordant note that
can be heard in addition to the two tones of the keys struck?  The lower
the 2 adjacent notes are in frequency, the lower the discordance or beat
note is.......... If the two keys struck are separated by one key in
between, then the discordant beat note is higher.  Separate the distance
between the keys sufficiently and the beat note becomes a subtle part of an
overall tone color.
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My method for setting zero ref uses a Shortwave Rcvr set to *AM* and tuned
to WWV.  The calibration of the Shortwave Rcvr needn't be accurate, jut
that WWV is tuned in clearly.    Remember that the Shortwave Rcvr is set to
AM, not SSB or any other mode.

The subject radio to be tuned is set to either USB, or CW(USB) with the CW
filter set as wide as needed to be able to hear the WWV tones, which is
also tuned to WWV and with the VFO indicator set to the exact frequency of
WWV.  10.000,000 MHz is usually fine for this but if you can receive a
higher WWV frequency it might work out better by making the lower frequency
bands even a hair more accurate.

Turn the volume up sufficiently and equally on both radios and listen for
the acoustic heterodyne when the reference tone comes on after the top of
the minute.  Tune the subject radio's reference setting until the audio
heterodyne that you hear from the speakers goes to null between the 2
radios.

Given th following:
SDR Radios, like the IC-7300 and others, may generate a symmetrical SSB
signal using the main VFO as the reference.  In which case just switching
SIDEBAND mode will not require retuning the main VFO back to WWV and
switching sidebands while listening to WWV should sound exactly the
same.    There should be NO difference.     If there is any difference then
re-check the reference tuning again on this side band.

Other radios, like my superhet FT-950, and FT-897d, generate USB and LSB
based on offsets in the IF circuit.   This means that switching sideband
mode most likely require retuning the main VFO by about 3 KHz to get the
exact WWV frequency again.  Since the FT-950 tunes in 10 Hz steps, it might
be a little more difficult to verify that USB and LSB sound exactly the
same and perhaps 'close enough' is the rule of the day.     It would be
best to tune these types of radios in the SSB or CW mode that most often
used.  If there is excessive error then the down stream circuitry that
generates sideband offsets may need looked at next.

Easy Peasy!

John at KB0NE, amateur radio station