Jason,
Yes, 2456 kHz IS way too low - in fact it is quite out-of -bounds - and is
close to only half the frequency that it should be.
First thing to check is soldering, then re-check the soldering, and when you
are finished, check soldering again. Use the schematic to identify those
components in the BFO area and check them carefully for good solder joints
and proper values.
Be certain the varactor diodes are the correct type, and be certain the
crystal the correct one and is properly soldered. The BFO is a VXO type
circuit, and if everything is proper, it would be very difficult if not
impossible to pull a good crystal by 50% of its frequency. If everything
else is correct, you may have a bad crystal (or perhaps it is shorted at the
solder joints by excess solder) - consider removing the crystal, cleaning up
the solder and putting it back in.
Lastly, look for something wrong with either the counter probe or the RF
voltage at the BFO test point. It is possible (but not probable) that the
voltage is high enough to properly count the frequency at the high end, but
drops off at the low end and counts only approximately half the pulses. If
you have a 'scope (or build the RF probe included with your K2 kit), it
should be able to tell you if the RF voltage is really lower at the low
frequency end.
The calibration of the 4 MHz reference may cause reading to be off by a bit,
but not nearly the difference you are reporting. If you set it with another
receiver, you are close enough for now - you can refine it later when you
have completed the K2 and are ready to do a precise dial calibration. I
recommend using the most recent method of zeroing WWV and comparing the BFO
and VCO frequencies (previously known as the N6KR method). Details are on
the Elecraft website and can also be found in the K2 dial calibration
article on my website www.qsl.net/w3fpr.
73,
Don W3FPR
----- Original Message -----
From: "Jason Marten" <[EMAIL PROTECTED]>
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 >=
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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