[Elecraft] K2 Frequency Alignment

[Don Wilhelm]

Rich and all,
One question - how are you getting the signal from the 4MHz oscillator.  If
you are connecting to any part of the circuit, you will be pulling the
frequency --- sooo when you adjust C22 to set it on 4.000...000 zero beat
with 20 MHz WWV, etc., it will truly be at 4.00000 with the probe attached,
but when you take the probe off, the frequency will be a bit higher - just
how much depends on the probe used.
Note: a high reference oscillator will result in you dial readings being
low!!!

To couple energy out of the 4MHz oscillator, I put the loose end of a wire
next to the casing of the MCU near the oscillator crystal and put the other
end of the wire into the antenna input of the receiveer I am using to listen
to the oscillator - couple the real antenna into the receiver too so you can
adjust the level of WWV so it is about the same as the reference oscillator.

I just completed alignment of a K2, and since this discussion was ongoing, I
tried a few experiments.  WWV was not too strong earlier in the day, so I
tried reading the oscillator frequency directly by putting my low capacity
10X 'scope probe on the hot side of C22 - The frequency counter said it was
over 100 Hz low, so I adjusted it up to read 4.000000, ran CAL PLL and tried
to find WWV - it was WAAAAY off, so putting even a low loading probe onto
the oscillator circuit is a no-no.

I did it my favorite method - plugged the internal probe into TP1, set K2
for CAL FCTR, and connected my counter also to TP1.  Then I adjusted C22
until the K2 FCTR reading is the same as my external counter.  Actually I
cheat a little, because I know at 19 MHz (the K2 was set on 20 MHz and I was
measuring the VFO) my counter is 45 Hz high.  After setting the reference in
that manner, and running CAL PLL, I found that 10 MHz WWV was 10 Hz low, 15
MHz was 12 Hz low and 20 MHz was only 15 Hz off.  I quit there because the
pressure of touching the adjustment slot on C22 with an insulated alignment
tool results in a change of 10 to 15 Hz and I had made fine adjustments many
times to compensate for this adjustment 'slop' before I got it to read the
same as my counter.

I have tried listening to the 5th harmonic of the reference oscillator
directly on the K2 tuned to 20 MHz WWV and have had no luck with it - I
cannot obtain a sufficienly strong signal without connecting to a part of
the oscillator circuit - and that pulls the frequency.

I don't know if I addressed your problem, but the exercise was educational
for me and I though I should let everyone know what I found.

73,
Don W3FPR
----- Original Message -----

I think I don't understand the K2 frequency calibration.  I have repeatedly
read on the reflector that if the clock is set for 4.00000000000 MHz you
will get good frequency readings.  After doing the Temp comp mod, I very
carefully aligned the K2 MCU oscillator by Zero Beating it against WWV at 20
Mhz.  This is confirmed audibly, a very slowwwww beat, and visually, when
the audio is piped to the MixW I get a fading track which goes solid when I
disconnect the antenna. The two signals are within 1/2 to 1/4 of a Hz of
each other.  I even fed the signal into the ant jack of the 706 and the two
signals are right on.   BUT, WWV at 10 Mhz is ~ 30 Hz low and WWV at 20 Mhz
is ~ 80 Hz low.  ( Upper and lower side band.) WHY?