[Elecraft] Do I have a problem? I do have questions! (long)

[Vic Rosenthal]

Max Moon wrote:

> 1.  In switching filters, the received CW signal changes pitch both up and
> down, depending on which of the four bandwidths is selected. In addition,
> the 2nd filter (0.7--all are at default widths) is muffled or noisy, unlike
> the others. (In other words, how much variation is acceptable--these changes
> are definitely beyond the 10-20 Hz DAC variation I read about.)

Hi Max,

Just redo the CAL FIL with the Spectrogram program.  It is possible to get the
pitches within 10/20 Hz. with arbitrary filter bandwidths.  If you hate having
ANY pitch change (I do), you can change the bandwidth of a filter by 20 Hz (for
example, I use 220 instead of 20) and then re-center the BFO and you will be
able to get the exact pitch on all filters.  Most likely the BFO frequency is
far off on the filter that sounds muffled.

> 3.  The OHR WM-2 (which I re-calibrated a couple of months ago) never shows
> 5W output, rarely shows 4W, & sometimes not even 3W, even though both the K2
> bargraph & LCD display show 5W. (Sometimes when I tune the antenna at 2W
> (indicated by the K2) the WM-2 shows 3W, and when I go back to up to 5W on
> the K2, the WM-2 is still less than 4W.) (The WM-2 is inserted between the
> K2 and the ATU & has seemed consistent in the past.)

If you don't have the KAT2, the power reading is likely to be incorrect when the
antenna isn't perfectly matched.  You can calibrate the K2 at 5w once you have
adjusted your tuner for a 1:1 SWR.

> 3.  What Rev. B mods do you think are essential for a CW/QRP-only K2? (my
> impression is that the "BFO Toroid & PLL Ref Osc Xtal Upgrade" and "2nd
> Filter Upgrade" make sense--do you agree?--but I don't know about any of the
> others...)

The BFO/PLL mod does improve stability. The second filter upgrade mod is for
SSB.  The 'better grounding of crystals' mod made a big difference for me as a
CW operator; also the 'modification of sidetone circuit' for a sinewave sidetone
was helpful -- it makes zero-beating easier.  I did not have a scratchy audio
pot, but if you do then you should make that mod.

> 5.  Are there any specific mods you'd recommend for a CW/QRP K2? (My
> thinking is that the 7-matched-crystal CW filter mod might help but I don't
> know what else, not even whether it's worth going all the way & doing the
> 14-crystal swap...)

If you want to do this, it's only 7 crystals for CW.  The 14 are needed only for
SSB.  However, many older K2's do not have a problem with the CW filter and
don't need this mod.  When you get your filters aligned with spectrogram, check
the additional attenuation at 200 Hz bandwidth.  If it is much greater than
about 3 DB you might want to do this mod.

I haven't answered all of your questions, but I'm sure others will or already
have!

73
Vic K2VCO