[Elecraft] N6KR's 4 MHz oscillator cal method for the K2

[Don Wilhelm]

John,
Switching between LSB and USB will only produce the same tone IF you have
properly set the BFOs for BOTH LSB and USB to produce this condition
beforehand - it is 'iffy' at best.

When tuning to the carrier you also must take care to know that you are
beating with the carrier instead of  the tone.  An AM signal transmitting a
single tone is actually transmitting 3 distinct frequencies - the carrier
plus 2 signals at the carrier frequency +/- the tone pitch, so when zeroing
the carrier, make certain you observe it during those minutes that the tone
is not present.

Your reaoning would be correct if the K2 used the same BFO frequency offset
(from the IF frequency) on both sidebands - the K2 does not do that, the USB
and LSB BFOs are independent - besides, if you can hear the same pitch in
LSB and USB without moving the VFO, you are not likely hearing the carrier,
but a demodulated tone.

If you need more information about 'why', take a look at the article dealing
with K2 dial calibration on my website at www.qsl.net/w3fpr, plus
information about the frequency spectrum of an AM signal (info in the ARRL
Handbooks), and the block diagram for the K2 in the manual to see how the
demodulation process is handled.

You can use the same technique tuning to any signal of known frequency, but
the arithmetic is not as easy - in LSB mode, subtract the frequency of the
BFO from the VFO and that should be the frequency the K2 is receiving.

If you must zero the carrier, I suggest you use CW mode instead of LSB or
USB and tune for a pitch equal to your sidetone frequency.  Use Spectrogram
to display the pitch of the demodulated audio squarely at your selected
sidetone pitch.  That will get the job done for you.

73,
Don W3FPR

----- Original Message ----- 
|
| I made the assumption I was splitting the difference of the WWV carrier
| which I thought would put my display at zero. Either that doesn't really
| work that way or I tuned to some other tone/noise in the area. I don't
know
| which. I sure hope there's not a third choice here. Anyway I found Gander
| Radio signal at 10051.36kHz, where the USB sounds right to me, which is
| supposed to be at 10051.00kHz.
|
| One question before I have to quit playing with this, IF I line up the
500Hz
| and 600Hz on spectrogram  at proper place on USB and change to LSB, should
| they still be in the right position? I was under the impression they would
| be.
|