The information on this page is not official information from Elecraft. It is merely my comments and observations about the Elecraft K2 radio derived from my experiences while working on the K2 radio I own.
The following comments about R21 and the PLL document behaviour I noticed while working on my K2. I am noting them for historical reasons (mine at least) and on the chance someone else may find them of interest some day.
While checking my PLL range, the PLL frequency looked good when I hit BAND+. When I hit BAND- the frequency dropped to 0. I discovered that one end of R21 was clipped so the resistor was no longer in circuit. Replacing R21 with a new resistor fixed the problem.
After replacing R21, I noticed a slight reduction in the PLL range. The measured value of the new resistor was slightly less than the one I removed. It appears that the range of the PLL is affected by changes in the value of R21 but only by a small amount.
There were a number of messages on the Elecraft mailing list from people having some trouble finding the right adjustment for L34. The following notes detail a procedure I developed which I feel takes some of the guess work out of the process.
In addition to the K2, this procedure requires a computer capable of running the Spectogram program, and an audio cable to connect the K2 and the computer.
In general, the procedure is as follows:
Set up your K2 and computer as if you are getting ready to align the filters. The main difference is that you need to tune the K2 so that you can hear the birdie on the 40m band (usually found near 7MHz). Turn off the AGC.
Start with the slug in L34 near the top of the can. Turn the slug of L34 clockwise to lower it in to the can. As you do this you should see the strength (height of the birdie as seen on the Spectogram display) increase. Stop turning the slug in L34 once you reach the point at which there is no further increase to the signal as seen in the Spectogram display.
Turning the slug in L34 past the point at which no increase in signal strength is observed will just result in an increase in noise. It was reported on the Elecraft mailing list that the best signal to noise setting for L34 may be about 1/4 to 1/2 turn BEFORE you reach the point of maximum signal.
This is not the only procedure for adjusting the slug in L34 but this should help make it easier than adjusting by ear alone.
Don't forget to re-run CAL S Hi/Lo after making any adjustment to L34.
The best way to calibrate the frequency display of the K2 is to use the N6KR method. I have two additional comments on the procedure. The second comment is important and will save you a lot of grief.
First, if a frequency counter is available, there is an alternative to zero beating against WWV on 10MHz. What I did was to connect a dummy load, turned the power down to about 0.5 watts (ie. only enough to get a stable reading on the external counter), tune to 10MHz, then use TUNE to measure the transmit frequency. I adjusted the VFO to get as close to 10MHz as possible (which might be above or below 10MHz).
Second, and most important, when you are about to adjust C22, make sure the frequency counter probe of the K2 is in TP1 (to measure the PLL frequency). This is important since small changes to C22 affect the measured frequency of the PLL more than they do the frequency of the BFO since the PLL frequency is three times the frequency of the BFO.
The N6KR method is an easy way to get the frequency alignment of a K2 as good as it can get. After following the procedure your worst case frequency error should be no more than about 50Hz. On my K2 (#2172) I had a frequency error of between 20 and 25Hz worst case at the top end of the 10m band.