Posted by
Don Wilhelm-3 on
Oct 11, 2006; 9:14pm
URL: http://elecraft.85.s1.nabble.com/k2-freq-readout-calibration-tp394462p394465.html
Carel,
The K2 does not use the 4 MHz oscillator in real time for frequency
determination, most of the time it only serves as the oscillator for the
microprocessor, so its frequency is not critical. That is why nothing
obvious happens when you change C22.
The 4 MHz Reference osc is used for frequency determination during CAL FCTR,
CAL PLL and CAL FIL. Before expecting accuracy with any of these menu
procedures, you must accurately set the 4 MHz oscillator beforehand.
If you did not accurately set the 4 MHz oscillator first, that alone may
explain your dial calibration error. Let the K2 warm up for about 1/2 hour
before starting the calibration cycle.
If you have an accurate frequency counter (known accurate to 1 Hertz or
better at about 12 MHz), then you can use the counter to set the 4 MHz
reference oscillator. Set the K2 to the 7 MHz or the 10 MHz band and
connect both the internal counter probe and the external counter to test
point TP1. Enter the menu for CAL FCTR and then adjust C22 until the
frequency displayed on the K2 matches the frequency shown on the external
counter. This method is outlined in the K2 manual.
If you do not have an accurate frequency counter, you can still set C22 with
accuracy as long as you can receive a station of known frequency. A
standard station like WWV is ideal, but other broadcast stations will
suffice if their operating frequency is known (an AM station is best). Tune
the station accurately in LSB or USB mode, then set the K2 menu to CAL FCTR.
Read the frequency at TP1, then read the frequency at TP2 and subtract the
two. Adjust C22 until the result of the subtraction is equal to the
transmitting frequency of the station you used as your 'standard'. This
procedure is the one available on the Elecraft website for download (it is
not in the K2 manual). The resulting accuracy does depend on your ability
to accurately tune the station (be certain to use LSB or USB, not CW because
of the CW offset). I like to use WWV because I can use Spectrogram to
display the 500 or 600 Hz tones and know that I have it tuned accurately -
other standard stations have their own transmitting format, check the one
that you can receive.
After accurately setting the 4 MHz oscillator (and before it drifts
significantly), run CAL PLL and then enter CAL FIL - tap BAND- and cycle
through each of the BFO settings, change each one (and then change it back
to the original setting if it was previously correct) to force the K2 to
write new values into EEPROM based on the new setting of C22. You must do
this for each and every BFO - 8 for SSB, 8 for CW and if you have the RTTY
filters set, yet another 8 BFOs must be set.
When you hgave finished all that, retune the station you originally used for
a standard, and you should find it now tunes within 20 Hz of the correct
frequency. If not, you did something wrong (or out of sequence) along the
way - the sequence is important, set C22 first, then CAL PLL and then CAL
FIL.
73,
Don W3FPR
> -----Original Message-----
>
> I have for some time (1 year) a well functioning k2. Never
> bothered to do a
> proper frequency.calibration because I used the k2 as IF for VHF.
> Recently I
> tried to do so (according to the w3fpr method), but no luck. I
> can't get the
> dial correct and have a quite big error (2 KHz or so). It seems that there
> is no change at all when performing the calibration (yes I do PLL CAL and
> XFIL CAL.).
>
> I do have one question to start with:
>
> If you tune to a carrier (CW) signal and adjust C22 (on the control board,
> to adjust the 4MHz xtal osc) what should happen ? Should the pitch of the
> carrier change ? should the frequency readout change ? (With my
> K2 "nothing"
> happens, no change in pitch, no change in readout, is this normal ?.).
>
>
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