K2 CAL PLL

[David J Windisch]

Hi, all concerned:

I get the operation of the hfo in general terms -- the PLL part, anyway.

I'm looking for (links to or) a fuller explanation of what happens in this
process: number of points, interpolation, etc.

TIA & 73, Dave, N3HE

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[Don Wilhelm-3]

Dave,

Have you read the information in the "Circuit Details" section of the K2
manual?  It contains a good description of  the synthesized VCO operation in
the RF board Sheet 1 section.  That information coupled with a careful study
of the schematic should give you the operation details that you request (the
DAC sizes are indicated in the schematic, so you can extrapolate the step
sizes from that info).  I am not aware of any documents that elaborate
further - the code in the firmware that drives all this 'magic' is Elecraft
proprietary.

73,
Don W3FPR

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

> Hi, all concerned:
>
> I get the operation of the hfo in general terms -- the PLL part, anyway.
>
> I'm looking for (links to or) a fuller explanation of what happens in this
> process: number of points, interpolation, etc.
>


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[Masleid, Michael A.]

Hi David,

>I'm looking for (links to or) a fuller explanation of what happens in this
>process: number of points, interpolation, etc.

To find out on your own, you could try this:

1. Get a stable CW signal source.
2. Get the spectrogram program.
3. Setup spectrogram for very high resolution.
4. Using CW mode, display the tone from the source in spectrogram.
5. Copy down the VFO setting and the tone frequency per spectrogram.
6. Change the K2 VFO setting by 10 Hz (don't change the signal).
7. Do steps 5 and 6 until the tone is at the edge of the CW filter bandwidth.
8a. Note the frequency per spectrogram
8b. Change the CW signal source frequency to get the same tone as in 4.
8c. Take the difference and write it down.
9. Do step 7(loop 5-6) and 8 until the signal is outside the RF filter bandwidth.
10. Plot the points as an X Y graph.

This will look like a saw tooth.  If you add back the differences recorded
in step 8c you can fix up the curve to get a ramp and see each interpolation point.  

Step 8b causes an error that accumulates, but over any short range you can see
how the K2 is setting the VFO.

A better procedure could be done with an old fashioned crystal calibrator, but
I think you'll get a feel for how the K2 works after looping through steps 5-8
a few times.

73 de Michael, AB9GV
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