[Elecraft] N6KR's 4 MHz oscillator cal method for the K2

[Dave Sergeant]

Wayne's method certainly is novel, but as GU3MBS says not necessarily 
simple for many builders. However the biggest problem in Europe is 
that we do not have a reliable frequency standard on 10MHz. The 
nearest is RWM on 9996kHz but that makes the arithmetic a little 
harder! It also only transmits a usable carrier for five minutes each 
quarter of an hour.

I re-calibrated my K2 a few weeks ago using my 20MHz signal generator 
checked against my frequency counter - the sig generator has an error 
in its reference so it cannot be used directly. By feeding its output 
to the CalFctr input I was able to adjust C22 to 10Hz at 20MHz. I 
seem to have got around 20Hz error at 10MHz checked against RWM and 
have the feeling this is as good as I am going to get it. In any case 
it is good enough for me... By the way, the counter has a 1MHz 
reference output, not high enough to get the required resolution.

One problem is that you cannot tune for zero beat in SSB mode as the 
zero beat frequency is out of the filter bandwidth. Tuning for best 
sounding audio on speech is dodgey if you are aiming at getting 
better than 10Hz. Tuning for a beat note against the sidetone 
oscillator (700Hz here) is the most sensible way but needs a stable 
non-keyed carrier - you cannot do this on the rapid keyed cycle of 
RWM.

The biggest problem is not being able to measure the 4MHz crystal 
directly with a counter. I tried various coupling loops etc but there 
is just not enough coupling to trigger the counter. It would have 
been nice if the internal oscillator was buffered to a test point 
where you could connect a counter, rather than relying second hand on 
reading it (deduced) via the inbuilt counter.

All interesting discussion, but I am not going to lose any sleep over 
a few Hz.

73 Dave G3YMC

dsergeant@btinternet.com
http://www.dsergeant.btinternet.co.uk