[Elecraft] K2 frequency counter question

[Don Wilhelm]

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.
>