[Elecraft] Frequency calibration - again
Don Wilhelm
Don Wilhelm" <[email protected]
Sun Aug 24 09:42:00 2003
Dave,
The sidetone frequency will not enter the picture if you use LSB or USB mode
(only CW). Use your Argo program to measure the pitch of the audio tone
rather than beating with the internal spot tone. In LSB mode, if you move
the VFO to receive the standard signal at a pitch of (say) 500 Hz (tune a 20
MHz signal at 20000.50) and then zero the reference harmonic at the same
pitch, you should have the job done.
If you are consistently 30 Hz off, you can compensate. Use CAL FCTR and put
the probe in TP1, then adjust C22 to move the count by 30 Hz (the actual
frequency reading doesn't matter, just the 30 Hz movement). Re-do CAL PLL
and CAL FIL and you should be right on (or very close).
Since you do have an external counter, I would recommend that you use it in
conjunction with the K2 internal counter (CAL FCTR) to measure the same
point (like TP1). Even if your counter is not calibrated, I will assume
that it has good short term stability. When the CAL FCTR reading is the
same as your external counter, the reference is set - do CAL PLL and CAL
FIL.
Now, since you don't know your counter's calibration - you may be off. Tune
to a standard frequency and see how much you are off. Then re-do the
measurement with both the internal and external counters, but set C22 so the
internal counter is lower or higher (as required) than the external counter
by the amount of your dial error. Run CAL PLL and CAL FIL again and you
should be a lot closer (if not right on).
73,
Don W3FPR
----- Original Message -----
| Last night I had another bash at calibrating my K2 using an
| alternative method similar to GU3MBS's Spectrogram method but using a
| program called Argo originally designed for reception of slow CW
| (QRSS) on 136kHz. This allows one easily to see and adjust signals
| seperated by 1Hz or less. I will give more details later, with a link
| for the software, but a couple of things I have noted first.
|
| The first thing I noticed is that it said my sidetone, set to 700Hz
| in my case, was at 710.3Hz, and a check with my counter confirmed
| this. What implications does this have in using the sidetone beat as
| a guide for exact tuning, and is this a common problem?
|
| The basic problem with adjusting C22 is that it is very difficult to
| set it precisely to frequency at 20MHz - it is easy to get it within
| 50-100Hz, but anything better is a natswhisker of an adjustment. I
| did manage to get it once within 2Hz, but it didn't stay there, any
| mechanical movement and it will move off by 10-20Hz or more.
|
| Of course I am still unsure how accurate the 1MHz reference in my
| counter is. End result last night is that I am back to where I was
| with the dial reading around 30Hz high on all bands.
|
| I intend to have another bash, but it really does seem to get the
| 1ppm accuracy claimed is hard to achieve in practice.
|