[Elecraft] Setting K2 Frequency Calibration

Thu Oct 31 21:16:15 2002

Hi

That sounds like a good method also. Just remember the 4.000 MHz clock is=
 only required during the CAL PLL routine, so long term stability is not =
required. It only needs to be exactly 4.000 MHz for a few minutes while t=
he calibration runs. The frequency counter is used to build the look up t=
ables in the EEPROM to calibrate the voltage controlled VFO. Once this is=
 done the counter is not even connected to the VFO.

You can improve the accuracy and cut the drift in half by removing X2 in =
the reference oscillator. As long as you can get a 10 KHz shift in the re=
ference oscillator as described on page 57, one crystal will work better.=
 If you can not get enough range swap the crystals or order a new set (Er=
ic told me all of the newer crystals have enough range so this should not=
 be a problem). This works because each step of the D to A converter chan=
ges the reference frequency a smaller amount with only one crystal and on=
e crystal is more temperature stable so you get a double benefit. I have =
done this on several K2's and it really makes a difference. You need to r=
e-run the CAL PLL after you remove the crystal or if you change crystals =
and of course the 4.000 Mhz oscillator needs to be right on for the calib=
ration using your favorite method. :-)

Don Brown
KD5NDB

----- Original Message -----
From: Ron D'Eau Claire
Sent: Thursday, October 31, 2002 6:00 PM
To: [email protected]
Subject: [Elecraft] Setting K2 Frequency Calibration

Earl makes an excellent point.

The way I set C22 in my K2 that is directly traceable to the National
Bureau of Standards was to pick a time when the WWV signal on 20 MHz was
audible on my auxiliary receiver. Then I arranged a pickup wire near the
K2 so I could hear the 5th harmonic of the 4 MHz oscillator in my aux.
receiver as well. It is easy to adjust C22  to put the 4 MHz oscillator
frequency within 1/4 Hz of WWV. That is, the 'swish' of the slow beat
between WWV and the oscillator signal as heard in the auxiliary receiver
was less than one every four seconds. That places the 4.000 MHz
oscillator to within 0.05 Hz of 4.0000000 MHz. That's much MUCH closer
than the temperature stability of the oscillator will be able to keep it
over time, so the accuracy of the K2 is then set entirely by the
stability of the oscillator and NOT by my calibration.

No "fancy" test equipment required, just a receiver capable of receiving
WWV on 20 mHz. That's sometimes a bit of a challenge because WWV runs a
much lower power on 20 MHz than it does on the other HF frequencies. It
may require a little messing around with the wire pickup for the 4.000
MHz signal from the K2 so it is not too strong or too weak. The "beat"
will be strongest when both WWV and the oscillator signal from the K2
are equal in strength. =20

And it is important to be sure that you are zero-beating the carrier
frequency of WWV and not one of the sidebands produced by the tone
modulation. That's easy to spot during the voice announcement. You
should hear the 'swish' of the beat during the voice announcement. If
your "beat" goes away when the tone stops, you've zero beated the
sideband and not the carrier. =20

Don't forget to run CAL PLL after adjusting C22, and going through CAL
FIL and changing each BFO frequency then resetting it to force the
system to re-calculate the frequency data stored in memory.  =20

Now any errors in the frequency display will be due to the oscillator
drift or the tuning algorithm, as Earl points out. =20

Ron AC7AC
K2 # 1289

... the #1 choice of setting C22 in the K2 manual is to set if for
exactly 4000.0000 kHz [and ignore any VFO frequency error].

73, de Earl, K6SE _______________________________________________

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