[Elecraft] More on N6KR method for setting the reference

[Ron D'Eau Claire]

I had my K2 open yesterday and a tuning tool was too close to my hands
and...

Curiosity got the better of me. Months ago I set my 4 MHz clock by zero
beating with WWV at 20 MHz, and the "dial accuracy" of my K2 had been =
within
20 Hz of the actual frequency since after a decent warm-up interval. =
Even
so, I gave Wayne's new procedure a try to see how it "worked".=20

I did NOT use Spectrogram, just my ears in both CW and SSB modes. As Vic
observed a while back, both USB/LSB comparisons in SSB mode and zero =
beating
against the SPOT tone in CW mode work FB. Wayne agreed with him about =
using
CW and noted that he had specified using SSB modes only because so many =
ops
have trouble hearing the 'zero beat' between the signal and sidetone in =
CW
mode.

Maybe I have a good ear for tones, I don't know. I'm not a musician. =
Still,
if I'm using SSB mode I find it easy to locate zero beat with WWV by
listening to WWV's tones while switching between USB and LSB. (Remember,
just press and hold the AGC button to hop from one sideband to the =
other).
If I'm off frequency it's obvious that one sideband is higher pitched =
than
the other. Adjusting the tuning eventually will make the sides switch: =
the
OTHER sideband will suddenly be higher pitched. For example, if at first =
USB
is higher pitched than LSB, there will be a point as I tune at which the =
LSB
is obviously the higher pitched. The frequency in the middle at which =
the
tones can't be told apart - or they are close as one can get - is "zero
beat" on SSB.=20

You can confirm that zero beat in CW mode is at the same dial setting, =
if
you are able to hear zero beat using the SPOT tone. If you've done CAL =
FIL
since the last time the filters were touched, CW should show zero beat
within 10 Hz of the SSB setting.=20

At the time I did my test yesterday, the dial read 10000.01 when I was =
zero
beat with WWV and sure 'nuf, the BFO/PLL frequencies were 10 Hz apart as
Wayne's procedure predicted.

Having been "Hands on" with the process of tinkering with C22 (again!), =
I
have a few notes that might help someone tacking it for the first time:=20

1 - The long term stability of the 4 MHz oscillator is NOT important. =
The 4
MHz clock only has to be accurate UNTIL you've run CAL PLL and CAL FIL =
to
record new values in memory. Once that's done, drift in the 4 MHz =
oscillator
or even changing C22 won't affect the dial accuracy unless/until you run =
CAL
PLL or CAL FIL again.=20

2 - The actual frequency of the sidetone is not important if you are =
zero
beating the received signal to it using SPOT. Whatever the sidetone
frequency is, the K2 offsets the displayed frequency that amount. You =
can
choose any sidetone frequency you want to use, and it doesn't matter how
close the sidetone frequency is to the indicated value.=20

3 - As others have noted, C22 is VERY TOUCHY! It can be a real pain
"tweaking" it. I use a nice small-but-solid METAL screwdriver. The metal
slot in C22 is at ground and I find that the metal shaft and blade have =
no
effect on the 4 MHz frequency. It's a lot easier to tweak the thing with =
a
screwdriver that is solid, fits the slot properly and which has a handle
much larger than any tuning wands in my tool box. Just don't let it slip =
and
short things on the board. A bit of stiff shrink tubing around the shaft =
is
good insurance. Shrink it tightly up away from the blade. Leave the end =
at
the blade unshrunk and cut flush with the end so it'll fit around the
capacitor adjustment screw and hold the screwdriver in place.

My K2 has all the stability mods in it. When I turn it on "cold", WWV at =
10
MHz is at about 10000.04 - 40 Hz high. After 15 minutes or so it is at
10000.02 or 20 Hz high. Over the next five hours or so it'll slowly drop =
to
somewhere around 9999.98 or 20 Hz low.=20

Ron AC7AC