[Elecraft] Usnig Spectrogram for Zero-Beating WWV, Frequency Calibration, and Filters

[frastephen@comcast.net]

K2 #2644 continues to be aligned!

There is serious lightning here in the Philly area right now, so #2644 is
disconnected from everything!  Hence, a good time to send along some
insights I had this evening.  Maybe this is old hat to everybody, but I am
pleased I figured this out and maybe it might help someone else.

Well, I wanted to calibrate the frequency of the VFO and align the filters.
So I downloaded Spectrogram (and registered it!  I used to be a programmer
in a previous life and I liked to eat, too!) and used it with N0SS's
wonderful instructions from the Elecraft web site for aligning the filters.
What a really great program (although, I wish the audio sent into the MIC
was also patched out to the speakers so you could listen to the audio as
well as watch it!).

I then realized I had not done anything to calibrate the frequency of the
VFO!  Oops!

Well, then I got an interesting idea ... why not use Spectrogram to get a
really close zero-beat of WWV?  You might remember that WWV sends precision
audio tones of various frequencies along with a 1000Hz "tick" each second
(details on their web site).  So I hooked it back up and Spectrogram gave a
really great display of these various tones and I was able to get a really
great zero-beat of WWV, which I used to ultimately do the adjustment to C22
for the 4 MHz Oscillator calibration (using the instructions from the
Elecraft website).  It took a few iterations of the procedure (I believe,
three), but in the end I believe I have the frequency calibrated to within
10 Hz (theoretically, I see from the Specifications on p. 5 of the manual
that the VFO accuracy is +/- 30 Hz).  Not bad!!!!  Probably as good as you
can get.

Then I used N0SS's instructions to do the alignment of the filters.

Then I got another insight!  Why not use Spectrogram to verify and make fine
tuning adjustments to the filters with a strong signal on a known
frequency....

So back to Spectrogram and I used it to monitor the audio from a certain
signal at 7047.5 kHz.  W1AW was blasting away, as usual here.  With the
frequency display calibrated I could tune it in right on the money (although
I have seen some posts about W1AW not being exactly WWV when it comes to
frequency stability -- never noticed it myself).  So I used that steady
signal to fine tune the filters exactly where I wanted them in the audio
spectrum across all four filters (8 actually, counting the CW RV settings).
Nice strong peaks at 600 Hz right across the board without tuning the VFO --
a steady tone across all the filters.

Bottom Lines:    I got everything aligned quite well!
                        I learned a lot about how the K2 VFO and filters
work!
                        I learned a lot about Spectrogram!

A worthy evening, if I do say so myself!

Fun and educational!

Well, the lightning has passed ....

Peace and 73,
Stephen
W3SMK
K2 #2644