[Elecraft] Setting K2 Frequency Calibration

[Ron D'Eau Claire]

Earl makes an excellent point.

The way I set C22 in my K2 that is directly traceable to the National
Bureau of Standards was to pick a time when the WWV signal on 20 MHz was
audible on my auxiliary receiver. Then I arranged a pickup wire near the
K2 so I could hear the 5th harmonic of the 4 MHz oscillator in my aux.
receiver as well. It is easy to adjust C22  to put the 4 MHz oscillator
frequency within 1/4 Hz of WWV. That is, the 'swish' of the slow beat
between WWV and the oscillator signal as heard in the auxiliary receiver
was less than one every four seconds. That places the 4.000 MHz
oscillator to within 0.05 Hz of 4.0000000 MHz. That's much MUCH closer
than the temperature stability of the oscillator will be able to keep it
over time, so the accuracy of the K2 is then set entirely by the
stability of the oscillator and NOT by my calibration.

No "fancy" test equipment required, just a receiver capable of receiving
WWV on 20 mHz. That's sometimes a bit of a challenge because WWV runs a
much lower power on 20 MHz than it does on the other HF frequencies. It
may require a little messing around with the wire pickup for the 4.000
MHz signal from the K2 so it is not too strong or too weak. The "beat"
will be strongest when both WWV and the oscillator signal from the K2
are equal in strength. 

And it is important to be sure that you are zero-beating the carrier
frequency of WWV and not one of the sidebands produced by the tone
modulation. That's easy to spot during the voice announcement. You
should hear the 'swish' of the beat during the voice announcement. If
your "beat" goes away when the tone stops, you've zero beated the
sideband and not the carrier. 

Don't forget to run CAL PLL after adjusting C22, and going through CAL
FIL and changing each BFO frequency then resetting it to force the
system to re-calculate the frequency data stored in memory.  

Now any errors in the frequency display will be due to the oscillator
drift or the tuning algorithm, as Earl points out. 

Ron AC7AC
K2 # 1289



... the #1 choice of setting C22 in the K2 manual is to set if for
exactly 4000.0000 kHz [and ignore any VFO frequency error].

73, de Earl, K6SE _______________________________________________