ANOTHER K2 FREQUENCY CALIBRATION TECHNIQUE
Glen Worstell, KG0T
March 19, 2003
For builders who do not have access to a counter, a marker generator, or
another receiver, the manual suggests a frequency calibration technique
involving zero-beating the receiver with WWV at 10 MHz. However, tuning to
zero beat within a few Hz is very difficult because the response of the
receiver falls off drastically at low audio frequencies (as it should).
An alternate method is to turn on the sidetone oscillator and tune WWV at 10
MHz so that the WWV carrier is heard at the same frequency as the sidetone.
By adjusting the receiver volume (and, if necessary the sidetone volume) so
that the two tones are about equal in amplitude it is fairly easy to find
the dial setting that is closest to zero beat. Because of the 10 Hz
frequency steps the best (lowest) beat frequency may be as much as 5 Hz,
which is still very easy to hear. It is best to do this during the short
time each minute when the WWV audio tone is off.
Because of the way the sidetone is implemented in the K2, the sidetone
frequencies are not exactly the values set in the sidetone pitch menu (ST
P), but the frequencies are known and are accurate to a fraction of a Hz
regardless of the setting of the 4 Mhz reference oscillator frequency (C22).
The relationship between the ST P settings and the actual sidetown
frequencies is not simple and is not known by the author, but the factory
kindly supplied the value for a ST P setting of 0.65.
Set the sidetone pitch to 650 Hz (0.65 will be displayed). The actual pitch
for this setting is very close to 660 Hz. Tune the receiver to 10000.66 KHz
(LSB mode), and you should be able to hear the WWV carrier. Turn on the
sidetone and slowly adjust the receiver frequency until you hear the WWV
carrier beating with the sidetone. You should be able to hear a very
distinct low frequency beat when you are close to the best setting. You are
not hearing the actual low frequency note, which will be only a few Hz, but
you will hear the tone rise and fall in amplitude at a rate of a few Hz.
The frequency of the beat note may be very close to zero, with one beat
every few seconds, or it may be off by as much as 5 Hz. You should be able
to hear the beat frequency increase if the dial is turned one step CW or CCW
from the setting that gives the closest match between the sidetone and the
The procedure outlined in the manual is then followed, except that the vfo
difference will be with respect to 10 Mhz PLUS the sidetone frequency of 660
Hz (if using LSB) or MINUS the sidetone frequency (if using USB). Important
note: the actual sidetone frequency, as described above, will be about 660
Hz when ST P is set to 650. Be careful not to move the K2 dial during the
You might want to leave ST P set to 0.65 and adjust the CW filters and audio
filters (if installed) to use this value. By doing so it is then easy to
check the calibration without removing the top cover. You can use any of the
WWV frequencies or the CHU frequency of 7.335 MHz.
This technique is accurate (within the limits of the K2 10 Hz resolution),
fast, and easy, and it requires no test equipment.