[Elecraft] K2 Frequency Alignment

Sat Jul 26 23:59:09 2003

I made up an inductive "probe" by winding a few turns of wire along the end
of a length of coax and putting shrink-wrap over it. The coax then connects
to my PRO2 receiver input where I can either use the 4 MHz signal directly
or use the 20 MHz WWV harmonic.

I lay the insulated coil end anywhere near the microprocessor chip and pick
up enough signal for the purpose without noticeably pulling the oscillator
frequency, per a precision counter also on the line.

The PRO2 has the sensitivity to allow the very small pickup signal to be
used. I use DigiPan as an audio spectrum analyzer to measure the 4 MHz
signal by tuning the receiver to 4.001 MHz and looking at the nominal 1000
Hz trace on the waterfall. DigiPan will read the actual frequency to within
an indicated 0.1 Hz.

I previously calibrate the PRO2 with WWV by first measuring the WWV audio
tone in AM mode to verify the soundcard/program operation. Any deviation
from  400 Hz or whatever is noted as a correction factor. Then I tune to WWV
at 10.001 MHz and look at the 1000 Hz trace. Any departure from exactly 1000
Hz +/- the soundcard factor is the dial calibration error of the PRO2 which
is then factored into the 4 MHz calibration. I usually keep the PRO2 to
within 0.5 Hz of WWV as measured in this manner.

I find that using the 20 MHz WWV signal to be far and away the most
accurate, but the other approach comes close enough to allow a fair degree
of accuracy.

Considering the many strengths and advantages of the K2, I am willing to be
lenient with respect to dial calibration accuracy, especially since the
architecture of the receiver simply will not permit much better than +/- 20
Hz at best on some bands and much more on others.

If dial calibration is of importance, I compare the K2 with the PRO2 and
note the difference. I then use that as a correction factor for the K2 for
that band and at that time.

The inductive coupling method is, I believe, the best way to tap off some 4
MHz signal with the least disturbance to the actual oscillator frequency.

73/72, George
Amateur Radio W5YR -  the Yellow Rose of Texas
Fairview, TX 30 mi NE of Dallas in Collin county EM13QE
"In the 57th year and it just keeps getting better!"
<mailto:[email protected]>

----- Original Message -----
From: "Ron D'Eau Claire" <[email protected]>
To: "'Don Wilhelm'" <[email protected]>; "'Rich Lentz'" <[email protected]>;
"'Elecraft Reflector'" <[email protected]>
Sent: Saturday, July 26, 2003 10:28 PM
Subject: RE: [Elecraft] K2 Frequency Alignment

The way I get plenty of 4 MHz signal without loading the oscillator for the
purpose of zero beating with WWV at 20 MHz is to connect a test probe in
parallel with the antenna at the K2 antenna. I touch the tip of the probe to
the metal CASE of the 4 MHz xtal. The case is, of course, at ground for DC
and very nearly so for RF, but there's plenty of leakage to drive lots of 4
MHz signal into the K2 receiver. Indeed, when the 20 MHz signal is strong,
the test lead picks up plenty of WWV signal too.

My problem lately with the whole procedure is that it's been a long time
since I heard WWV on 20 MHz here in N.W. Oregon. I read that they are
working on a reduced schedule on 20 and 25 MHz and wondered if they off the
air. Are others hearing the 20 MHz signal? The lower frequency signals are a
reliable as ever, of course.

Ron AC7AC
K2 # 1289

_______________________________________________
Elecraft mailing list: [email protected]
You must be a list member to post to the list.
Postings must be plain text (no HTML or attachments).
See: http://mailman.qth.net/mailman/listinfo/elecraft
Elecraft Web Page: http://www.elecraft.com