From: Masleid, Michael A.
Dated July 28, 2003
Subject: RE: K2 Frequency Alignment
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Hello Don,
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
>frequency!!!
>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
adjusted.
>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