[Elecraft] 4 Mhz Oscillator calibration

[Ron D'Eau Claire]

Andreas, If you are trying to find the setting of C22 to put WWV right
'on frequency' use 10 MHz. But that still may not be optimum. 

The problem with trying to make WWV "right on" 10.00000 KHz is that the
4.000 MHz oscillator might then be off 4.000 MHz due to some tuning
uncertainty in the K2 firmware. It's not "perfect". 10.000 MHz is the
"low end" of the 30 meter tuning range (it'll tune further, but
according to the Elecraft documentation, is the recommended frequency to
use if you are trying that method). So it will be closer to "right" than
the other WWV frequencies. Still it's not "perfect". Expect 20 or 30 Hz
error. 

A better way is to set the 4.000 MHz oscillator directly to zero beat
with WWV. Unfortunately, WWV does not have a signal at 4.000 for you to
use, but you can use the fifth harmonic of the oscillator and beat that
against WWV at 20 MHz, since you obviously can hear that. If you can't
hear WWV at 20 MHz, you MAY be able to use WWV at 15 MHz (see below). 

Tom H asked me to write up a procedure for this, and I have been working
on it with another op. We are still working on it but here's what seems
to work best: 

Let your K2 warm up for at least half an hour. An hour or more is
better, especially if your "shack" is cool.

Select CW mode.

Press and hold the MODE button so it is NOT possible to "key" the
transmitter. 

Tune in WWV on 20 MHZ and zero beat the carrier with your SPOT function.
It may not be exact. It can be as much as 5 Hz off, since the K2 tunes
in 10 Hz steps. But a 5 Hz "error" at 20 MHz is only a 1.25 Hz error at
4 MHz. That's more accuracy than the K2 can use. 

Once you have WWV zero beat with the SPOT command, press and hold the
RATE button to LOCk the tuning so you can't 'bump' it. It's very
important that you not disturb the tuning. 

Disconnect the antenna and connect a test lead to the antenna jack. A
DMM test lead works very well for this if you have a banana jack adapter
for your K2 or have the KPA100 installed (The SO-239 coaxial connector
on the KPA100 takes a banana plug in the center hole). 

Touch the other end of the test lead to the metal "can" of the crystal
on the Control Board. You should be hearing the fifth harmonic of 4.000
MHz crystal oscillator very clearly along with the SPOT tone now. You
can confirm that you are hearing the 4 MHz crystal oscillator by
touching the metal crystal can with your finger, or reaching under the
crystal to C22 and touch it with your finger tip. Doing that will move
the oscillator frequency and you should hear the beat note against the
SPOT tone change.  

NOTE: If you have the KPA100 installed and seem to have a lot of
interference with another strong signal, you may be hearing the 4MHz
oscillator in the KPA100 itself. The frequency of that oscillator is
unimportant. It will not hurt to move it well off of 4 MHz by adjusting
C27 on the KPA100 board. Indeed, Elecraft recommends tuning it above 4
MHz if you find interference form it at the "top" of the 75 meter band. 

Once you are sure that you are hearing the Control Board 4 MHz
oscillator beating against the SPOT tone, adjust C22 for zero beat. It
may be  "touchy", since all changes are magnified five times because you
are listening to the fifth harmonic of the oscillator. But that also
means that small errors don't matter.

Next, tune your K2 to 40 meters and run CAL PLL and CAL FIL to make the
firmware re-read all the frequencies and store new tuning values. You
are done! 

WWV may NOT be EXACTLY at 10.000 or 15.000 or 10.000 MHz even after
doing this, but the tuning errors will be minimized across the whole K2
tuning range. 

FOR OPS WHO CANNOT HEAR WWV at 20 MHz, I have noticed that there is a
harmonic of the 4 MHz Control Board oscillator audible on 15 MHz in my
K2. Actually it is a harmonic of some counted-down signal derived from
the 4 MHz oscillator, but it seems dependent upon the frequency of the
4MHz oscillator only, as far as I can tell. It is not as strong as the
5th harmonic of the oscillator at 20 MHz, but it is clearly audible in
my K2 with the test lead touching the crystal can itself. You can use
the same procedure at 15 MHz by listening to this signal. If anyone
tries this with your K2, I'd like to know how it worked for you. Again,
you can confirm that it is the 4MHz oscillator on the control board that
you are hearing by touching the top of C22 with your finger and hearing
the beat shift. 

Indeed, I'd appreciate any comments folks have about his procedure. You
can drop them to me personally to hold down the reflector traffic. I
will gladly use the inputs when assembling a procedure with details for
Tom and the Elecraft guys to look at before I forward it to Tom to put
it on his web site. 

Ron AC7AC
K2 # 1289