KV5R: Icom IC-706MkIIG Mods and Tips
3. Repeatedly adjust the VR, very carefully, until no frequency shift is seen on the computer. It is
possible to get within 1 Hz.
4. Note: Your computer soundcard clock may not be calibrated, so you may not see 600.0 Hz on the
status line frequency readout. Simply adjust the VR until the numbers are equalized between CW
and CW-R modes. Afterward, you can adjust your soundcard clock (in MixW) to make it alternate
599.9/600.0 (in AM mode) and then your computer will also be calibrated.
5. When satisfied, replace the cover and return the room to normal temperature.
Testing the Frequency Calibration, Notes:
1. Accuracy increases on lower frequencies and decreases on higher frequencies. For example, if it is
off 1 Hz at 20 MHz, it will be off 0.5 at 10, or 0.25 at 5 -- or 10 Hz at 200 MHz and 20 at 400.
Hence, Icon Service (and the Service Manual) will tell you to calibrate the radio using a lab-grade
Service Monitor or Frequency Counter at 60 MHz or higher. However, even the best lab-grade
, the broadcast of the US NIST cesium atomic clock, so I
recommend just bypassing the Service Monitor and using WWV directly, at its highest frequency,
20 MHz, and getting the Master Oscillator within 1 Hz in a temperature stabilized room.
2. Many do not know that the modulated audio tones on WWV are also Frequency Reference
Standards. The "beep" at the top of each minute is exactly 1000 Hz; the continuous tones (when
on) alternate between 500 and 600. Thus, you can listen to WWV on AM and get an exact 500 or
600 Hz tone, then switch to LSB and USB and compare them with the true tone heard on AM. You
can also beat a 500 or 600 Hz offset tone against the 500 or 600 Hz modulation, when available,
but this beat is hard to hear below a few Hertz.
3. To periodically test the calibration, simply return to 15 or 20 MHz (exactly) and repeatedly switch
between CW and CW-R, comparing the tones. You’ll see it go off a little when the room
temperature is not normal, and when the radio is heated up from lots of transmitting, but it
shouldn’t be more than 2-3 Hz off, at 20 MHz.
4. You can determine your exact error by connecting to a computer and reading the frequency
differential between CW and CW-R. Divide the differential by two and that will be your error
(readable to - 0.01 Hz using MixW.) If you then QSY down, divide the new frequency by
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