[Elecraft] K2 BFO Test: BFO low freq is really low

[Ron D'Eau Claire]

It looks like the counter is only registering half the frequency and it's
really at 4912 kHz. 

I don't think it's physically possible for the BFO to oscillate down there.
Certainly not under crystal control. C22 won't vary your counter time base
enough to cause anything like that sort of error. You can confirm that he
counter is working by simply going back to the other end of the range where
you read 4917.54 kHz and confirm it still works. 

I'm really stumped to suggest where it might be happening though. I'd say
the counter but if you get a good reading at 4917.54, I don't see how that
could be it.  

Ron AC7AC

-----Original Message-----
I've come to the Alignment and Test, Part II.  I think I'm having a problem 
under the BFO test.

Following the instructions, I switch to 40m, hook up the frequency counter 
to TP2, and get a reading of 4913.52.  The manual says I should get 
something between 4908 and 4918.  So far, so good.

Next, I go to the part where you determine the BFO range.  After hitting 
Band+, I get a reading of 4917.54 kHz.  The manual says you need >=
Band+4916.3,
and it's usually between 4916--4917.  Maybe a tad high, but looks good to 
me.  After hitting Band-, I get a reading of 2456.11 kHz.  The manual says 
it must be <= 4912.7 (which it most certainly is) but it is usually about 
4909--4912 (which is isn't, by a long shot).  This results in a range of 
2461.43.  The manual says it must be >= 3.6 (which it is, by a lot), but 
it's typically 4--6 kHz.

It looks like I'm meeting the letter of the law based on the >= and <= 
requirements, but I'm nowhere near the typical ranges on the BFO low freq. 
and range.

Following this test in the manual is some info on what to do if the 
frequencies are too high or too low:

First off, I did not use a frequency counter to adjust C22 on the control 
board,   I used a separate receiver and hooked up a wire from its antenna 
jack to the 4 MHz crystal, as described in the manual.  This resulted in me 
turning C22 less than 30 degrees counter clock wise (anti clock wise).  This

seems reasonable to me, so I don't think C22 is off by very much.  However, 
I think I might want to try using a frequency counter, to get a little more 
accuracy in calibration.  Could anybody recommend an affordable frequency 
counter?  I've never shopped around for them, so I have no clue as to the 
price, etc.

The third point mentions I might have shorted out part of L33.  Looking 
under a loupe, I did not see any evidence of a short, and in fact, I can 
slide L33 underneath R116, it doesn't appear that heating R116 affected L33.

The fourth point mentions L33 could be broken.  I put my DMM on the tiny 
leads attached to R116 and got 1.7 Ohms.  Does this sound reasonable?

The final point says to check the capacitors and diodes in the BFO circuit.

After another quick look, this appears to be OK to my eyes.

Any help would be appreciated!


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