From: Masleid, Michael A.
Dated July 28, 2003
Subject: RE: K2 Frequency Alignment
I think this is a bit more complicated.
>You have hit the nail on the head.
>Attaching anything to the 4 MHz oscillator circuit will pull its
>My rule of thumb - never attempt ot measure the frequency of an oscillator
>by connecting to the oscillator section - measure after a stage of
>buffering, or use indirect pickup methods.
There is an exception. When you measure the frequency of the reference
oscillator of a counter with the counter itself, it should show the same
value, regardless of what frequency it is actually running at. A one foot
ruler is exactly one foot long, if you use that same ruler to measure itself.
>Sooooo - when one attaches a probe, adjusts it to exactly 4000.00 kHz, then
>removes the probe, the oscillating frequency is NOT 4000.00 kHz anymore.
Understood. To compare the 4 MHz oscillator to other signals, I hang a wire
clip near the top of the crystal. To make sure I'm not messing up the
oscillator, I watch the signal get lost in the noise as I pull the clip
away from the control board.
>Bottom line - don't do it that way!!! Apologies to the experienced folks
>who already know that, but I fear there are several looking and listening
>who are not aware of the consequences.
This method is per step 3, page 45 of the Owners Manual, revision E. Not
useful for setting C22, but certainly a good way to test the counter. In
my case, in step 3, I get 3999.98 kHz. It doesn't change when C22 is
>Since CAL FCTR is only accurate if the 4000.00 kHz oscillator is correct,
Are you very sure of that? For some reason, on #3430, CAL FCTR gives results
that are 5 parts per million low when the oscillator is set to 4 MHz. Is
it possible that the correct value for the 4000.00 kHz oscillator is about
4000.02 kHz in my case?
>using CAL FCTR to measure a known external frequency (such as a stable
>oscillator) and adjusting C22 until the display shows the correct frequency
>of that external oscillator is an excellent method.
>Just be certain that you do know the frequency of that external oscillator.
>The finished product is only as good as the tools used to produce it.
I agree fully. Another method involves measuring an unknown oscillator that
is at least stable. Calibrate the K2, and check error against WWV and other
known standards. Use the error to extimate exactly what the unknown must have
been, and adjust C22 to display that frequency for the unknown oscillator.
Calibrate the K2, and check error against WWV again, repeat as needed.
73, Michael, AB9GV