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

[Ken Wagner]

Good morning all:

A few days ago someone reported that they followed this "new" procedure and
ended up 500-600 Hz off freq... I don't remember who, but it made me
curious, 'cuz the math says it has to work.

This morning I warmed up old #920 and tuned to WWV on 10 MHz on LSB. Using
Spectrogram, I tuned to put the 600 Hz tone under the 600 Hz marker in
S-gram, measured the VCO freq (14913.41) and the BFO freq (4913.42). This
indicated ~10 Hz off.

I then switched to CW mode, and zero-beat the carrier tone against the K2
sidetone and got the following results... VCO = 14913.89; BFO = 4913.30. The
difference is ~590 Hz. Hmmm... that's the sidetone pitch I have set in. I
checked with lowest pitch (400Hz) and highest pitch(800 Hz) and the results
track. So if one attempts to adjust C22 in CW mode so that the VCO - BFO
exactly equals the display freq, then does the CAL PLL and CAL FIL, the
result will be off by approximately the amount of the sidetone pitch. This
makes sense because that is the way the K2 generated the CW offset during
Rx.

So to use CW mode for this method by zero beating the carrier against the
sidetone, one must account for the sidetone pitch/CW offset that is set in
the K2. The equation would be:
        Tuned freq(10Mhz in this case) = VCO - sidetone pitch - BFO

All with the usual caveat that one must make _sure_ that he is zero beating
the carrier freq and not the occasional 500 or 600 Hz tone from WWV.

BTW... I didn't make any adjustments to C22 'cuz <= 10 Hz is OK for me.<g>

73, Ken K3IU
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

----- Original Message -----
From: "Wayne Burdick" <n6kr@elecraft.com>
To: "Vic Rosenthal" <vic@rakefet.com>
Cc: "Elecraft" <elecraft@mailman.qth.net>
Sent: Wednesday, August 20, 2003 22:36
Subject: [Elecraft] Re: N6KR's 4 MHz oscillator cal method for the K2


| This would work, Vic. I didn't mention it because historically we've found
that
| many people have trouble listening for a beat-note. But this would make a
good
| addition to the procedure.
|
| tnx
| Wayne
|
|
| Vic Rosenthal wrote:
| >
| > Wayne Burdick wrote:
| >  > Use USB or LSB mode rather than CW, so that there will be no CW
| >  > receive offset.
| > ...
| >  > TIP: Zero-beat the carrier precisely, or listen to a voice signal and
| >  > adjust the VFO for the best quality.
| >
| > Would it not be as good to use CW mode and tune for the slowest beat
| > after holding SPOT?  I find this much easier than trying to find
zero-beat.
| >
| > Or would this introduce some inaccuracy?
| >
| > Vic K2VCO