Jim,
Of course that can be done. You would need to construct a coaxial
counter probe similar to the internal probe (with a 10pF capacitor in
series with the tip), but unlike the internal probe, you would have to
provide a ground lead to the shield near the tip end. (the internal
probe depends on the K2 PC board ground for the return path - that does
not exist with an external device).
The length of your "probe" coax may reduce the maximum frequency that
can be used. With a short probe, the counter is good to 40 MHz.
The K2 display is limited to 10 Hz resolution, and its accuracy is
dependent on properly setting the 4 MHz reference oscillator. You can
check that by tuning to WWV in SSB mode and using the N6KR method to
determine the correct setting.
The details of how to do that are on my website www.w3fpr.com K2 Dial
Calibration article. The use of Spectrogram to determine that the
transmitted audio tones are received at the correct frequency. If you
need Spectrogram, you can download it from my website opening page -
look near the bottom for the links. I have versions 5.17 and version 16
there.
73,
Don W3FPR
On 10/29/2018 2:53 PM, Jim KO5V wrote:
I have what may be a stupid or naive question: has anyone used the built-in
frequency counter in a K2 to measure the frequency of a circuit external to the
radio?
I found what may be a reference to this, done by a French ham, but his link no
longer works. If this is possible, any info (especially potential gotchas)
would be greatly appreciated. I have built a couple of nixie-tube clocks as
Christmas gifts, and I need to adjust their internal frequency references. The
output is a 400khz, TTL level square wave. I know I probably need more
precision that the K2's counter may have, but right now, I just want to get as
close as possible.
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