[Elecraft] [K2] VFO alignment & display accuracy

[Don Wilhelm]

Sean,

Check the value of C21 - if should be a 33 pF disc ceramic capacitor.  
If you put the blue capacitor labeled 331 into the C21 position, the 4 
MHz reference frequency will be too low and you will not be able to get 
the counters to match.

Your BFO and VFO frequencies are within the realm of sanity, so that is 
not the problem.  The problem is with the frequency of the 4 MHz 
reference.  That is controlled by C21, C22 and X2 alone.
You should have a red dot on C22.

If the capacitors are correct, it may be that the 4 MHz crystal is off, 
and that would be the first thing I would replace.  If you have to order 
parts, I would suggest you get new parts for X1, C21, and C22 at the 
same time - the extra cost for the capacitors will be less than $1.00.

73,
Don W3FPR

On 4/16/2014 4:55 PM, Sean Michael Johnston wrote:
> Don,
>
> Thanks for the quick response.
> I gave this a try and went the other direction with the counter. Now after running PLL, my offset is further off (120Hz).
> I am still not able to get the BFO and VFO counters to line up. Turning the other direction put me closer the 120Hz offset above.
> I have been using the methods found on your website by N6KR in LSB mode zerobeating to the 600Hz tone of WWV by using the “Spot” function.
> When moving the probe from TP1 to TP 2, I cannot get the counter to line up any closer than 70Hz, no matter how many directions I turn C22.
> This is why I believe it is a hardware issue.
>
> - Sean K5SMJ
>
> On Apr 16, 2014, at 2:23 PM, Don Wilhelm <w3fpr at embarqmail.com> wrote:
>
>> Sean,
>>
>> If the BFO (TP2) is at 4913.05 and the VFO (TP1) is at 14912.97, then the frequency read at TP1 must come *up* in frequency by 9 to 10 Hz.
>> In other words, the count *must* rise.
>>  From what you said, the count will rise above 14912,97, and that is exactly what you want.
>> The count for the VFO will move about 5 times faster than the BFO, so try setting the count at TP1 at 14913.07 as your first guess, then check TP2 - it should be near 4913.07 - if not make minor adjustments until the 3 low order digits in both counter displays are the same when properly tuned to WWV.
>>
>> On tuning to WWV, you must do that is SSB mode, and the carrier will be at zero frequency (which you cannot hear).  I recommend you use Spectrogram or other audio spectrum analyzer to show you the frequency of the tones transmitted by WWV.  The 1 second tone every minute is at 1000 Hz, and the normal tones alternate between 500 and 600 Hz with a 440 Hz tone 2 minutes after the hour.
>> Tune the VFO to align those tones at the correct frequency.
>>
>> If you do not have Spectrogram, you can download it from my website www.w3fpr.com.
>>
>> Note that after running CAL PLL and CAL FIL, the count frequencies will be different than they are now.
>>
>> You might want to review the K2 Dial Calibration information on my website www.w3fpr.com.
>>
>> 73,
>> Don W3FPR
>>
>> On 4/16/2014 1:18 PM, Sean Michael Johnston wrote:
>>> I have been trying to get my VFO aligned by adjusting C22 based on the methods recommended by N6KR and as posted in the app notes on the Elecraft website - http://www.elecraft.com/Apps/notes_on_adjusting_c22.htm.
>>> I can never get it closer than 70 Hz. I am using the 10MHz WWV signal for reference. When I switch between TP1 and TP2 the closest match I can reach is between 4913.05 and14912.97. I tried to adjust for a -70 Hz offset while connected to TP2, but 14912.97 is as far as the I can go before the count starts to rise again.
>>> I saw an older post where Don W3FPR mentioned changing C21 to a different value. Would this solve my issue, and if so, are there any suggestions as to which value I should use?
>>>
>>
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