[Elecraft] MCU frequency adjust

[Don Wilhelm]

Ed,

You really don't need the reference oscillator adjusted 'right on' until you
have the entire K2 tuned and are ready to finally set the dial calibration.
When you are ready for that, the 'N6KR method' will provide the best
results.  See my website (www.qsl.net/w3fpr) article on K2 Dial Calibration
for more information on that subject.

For right now, setting it close will be OK, but if you would like to get it
within range now, here is my recommendation for 'how to do that':

If the frequency of the reference is too high, you could try increasing the
value of C21 (C21 and C22 are series connected across the oscillator
crystal, so increasing C21 will also increase the range of adjustment) - but
check to see that the value of C21 is 33pf first.

OTOH, if the reference frequency is too low, check that you do have the
correct value for C21.  Decreasing the C21 value will reduce the range of
adjustment and should raise the frequency too.

It is possible that your crystal is not right on frequency (there are a few
like that - mine was high), so if you have enough range for an adjustment,
you could try several small value capacitors (5 to 50 pf is 'small') either
across C22 or even directly across the crystal until it is at the proper
frequency.  Although Elecraft would likely ship you a new crystal if you
ask, I personally would rather just trim it a bit rather than waiting for
the new crystal and going through the checks again.

There is an advantage to having a small range of adjustment for C22 because
it becomes more difficult to adjust if the range is larger.  I would prefer
to settle for a small tuning range which is adjusted by the use of small
trimmer caps if I had a choice.

73,
Don W3FPR

----- Original Message ----- 

I am at RF stage 2 test.  I cannot adjust the frequency with c22 to agree
with my HP counter.  The internal counter is very close to the hp while
looking at tp3, and only needs to move a few hertz, but it only seems to
move a couple of hertz across the tuning range of c22.

I put a scope on one side of c21 and see the 4mhz sine wave at the mcu.
Tuning c22 mostly affects the amplitude, and the frequency stays nearly
constant (according to the internal frequency counter in my tek scope).