David,
The same principles work fine for any known frequency, it is just that
the subtraction of the BFO frequency from the VFO frequency is not as
straightforward.
An AM station broadcasting standard and constant tones (such as WWV) is
easiest because one can observe the demodulated audio tones with
Spectrogram assuring accurate tuning. If you have a good ear, you may
be able to tune to a station broadcasting music to within 5 or 10 Hz.
If you do use an AM broadcast station without standard tones as your
standard, I would suggest that you tune it by ear in LSB or USB first,
then switch to CW while observing the audio with Spectrogram - the
carrier should appear 'straight and tall' at the frequency you have set
in the K2 for the sidetone pitch - thus assuring accurate tuning of the
station. Then go back to SSB mode to set C22 while doing the
subtraction between the VFO and BFO frequencies. A note to help - any
adjustment of C22 will move the VFO frequency reading about 5 times
faster than the BFO reading, so do the adjustment with the counter probe
plugged into TP1 and then check the result in TP2. A few trials should
yield an accurate setting.
73,
Don W3FPR
David Woolley wrote:
Don Wilhelm wrote:
refer to the K2 Dial Calibration article on my website
http://w3fpr.qrpradio.com for techniques to accurately set the 4 MHz
reference oscillator and the following steps to achieve good dial
calibration.
Unfortunately, the sun doesn't seem to favour picking up WWV. The
original calibration was against the MHz birdies on an FRG7, which
was, I think, calibrated against WWV in the past. However I just
tried on some 41m broadcast stations, and it looks like the
calibration might be 30 to 40 Hz high on that band, which probably
equates to 50 to 70 Hz, in the same sense, on 10m, so I may try a
calibration against those broadcast stations. (Does anyone know a
relatively accurate broadcast station, receivable in a noisy location
in the UK, and near the high end of the VFO range?)
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