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

[Baker]

On Fri, 22 Aug 2003 10:20:17 +0100, Dave Sergeant wrote:
>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
>
>
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I have been following the thread and would like to forward my=
 2p's 
worth.

a) No adequate reception of HF frequency standard transmissions=
 in 
the UK. Radio 4 on 198 khz is a possibilty, but not a simple 
solution.

b) Zero beat/voice characteristics also very subjective as=
 previously 
mentioned. Maybe if the audio could bypass all the filtering for=
 
setting up we could hear 10 Hz ?

My method:-

Set FT1000MP to AM and generate a few watts into a dummy load.
Use frequency counter to measure the frequency and set to 10Mhz 
exactly.
Connect Chan A of dual channel scope across dummy load and=
 trigger of 
Chan A.
Wave probe of Chan B around near 4MHz oscillator until sufficient=
 
pick up.
Connect K2 internal probe to TP1.
Adjust C22 until trace B stationary with A.
Run CAL PLL.

SIMPLE !

I am assuming that my counter timebase is correct. Anyone know=
 how to 
check it without an on-air frequency standard ?

73

Stewart G3RXQ
-- The Bakers' Home
-- baker@nildram.co.uk on 22/08/2003