Accurate Adjustment of K2 BFO frequencies for CW
Although this subject is well covered already with appropriate links to
procedures provided on the Elecraft website, I thought I would share my own
procedure for adjusting the BFO frequencies. This procedure does not require
the use of a spectrum analyzer or spectrum analysis software, so does not
provide frequency response curves. However, I believe it to be as effective and
accurate as other recommended procedures for centering the filter passbands at
the desired CW pitch.
My procedure requires an RF signal source with stable amplitude and frequency
(I used the Elecraft XG-2), and an instrument for measuring audio pitch (I used
an MFJ-784B DSP audio filter, adjusted as described, with a pair of
The procedure is as follows:
1. Use the CAL FIL procedures in the K2 manual for selecting the four desired
XFIL bandwidths. (In my case, I used 0.35, 0.30, 0.20, and 0.15 KHz
2. Use the St P menu function to set the desired CW pitch. (I use 0.40 KHz).
3.Use the XG-2 Signal Calibrator to calibrate the K2 s-meter, as described in
the K2 manual.
4. Keep the XG-2 connected to the K2 antenna input. Connect the K2 headphone
output to the receive audio input of the outboard audio DSP filter. Use
headphones to monitor the audio output.
5. Setup the outboard DSP audio filter as a bandpass filter centered at the
desired CW pitch frequency (same frequency as selected in Step 2). Adjust the
bandwidth of this filter to the minimum possible (30 Hz on the MFJ unit). Note:
the MFJ -784B provides a Morse code indication of the exact center frequency
6. Setup the XG-2 to 50 microvolts output at one of the three available
frequencies (I used 7040 KHz).
7. Select FL 1 on the K2. Tune the K2 for maximum s-meter deflection from the
XG-2 signal source. Do this as accurately as you can. I used the K2 preamp to
get as many of the s-meter LED's lit as possible, making sure the s-meter was
8. Now use the CAL FIL procedures outlined in the manual to adjust the BFO
frequency for maximum audio output (from the outboard narrow audio filter set
up in step 5) in the headphones. Using the 30 Hz audio bandwidth of the MFJ,
the peak was unmistakable among only a handful of audible choices limited by
the resolution of thef BFO frequency setting.
9. Repeat steps 7 and 8 for the other XFIL bandwidths and for CW RV at each
This worked well for me.
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