K3 frequency accuracy versus displayed precision

Posted by Paul Kirley on Nov 17, 2009; 2:28am
URL: http://elecraft.85.s1.nabble.com/K3-frequency-accuracy-versus-displayed-precision-tp4016138.html

The K3 is capable of displaying frequencies to 1 Hz.  It can
be calibrated to somewhat less than 1 Hz against WWV (method 2).

Because I wanted to see if my K3 serial 1322 was capable of
measuring frequency to its displayed precision, I decided to
attempt the November 11/12 ARRL Frequency Measuring Test.

I warmed up my K3 for about two hours because--even with the
optional TCXO--my K3 drifts almost 0.1 ppm per degree Centigrade
from 25C to 30C, the latter part of its warmup range this time
of year at my QTH.  (0.1 ppm is almost 1 Hz on 40 meters.)

Then I carefully used method 2 to calibrate against 10 MHz WWV,
checking after exiting REF CAL by tuning across WWV on CW with
SPOT activated to see that the beat notes were similar on each
side of zero beat for 1 and 2 Hz off frequency.  (A lack of
similarity indicates that a small tweak of REF CAL is needed.)
Tuning past WWV's carrier on CW with SPOT enabled also provides
practice for the real thing.

When W1AW (and each of the other FMT stations) began its call-up,
I tuned its frequency to be centered in the passband with the DSP
set at 50 Hz bandwidth.  When the long dashes began, I turned on
SPOT and zero-beated against the sidetone with 1 Hz fine tuning.

After recording the result, I moved on to the other frequencies
and stations that had been specified in the ARRL FMT
announcement.  I was able to copy and measure 4 of the 5 tests,
with one station on one frequency being inaudible at my QTH.

Result:  my K3 was within 1 Hz on all 4 readings, that is, its
accuracy matched its displayed precision--after warmup and
careful calibration.

73, Paul W8TM

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