Your off frequency OM!

WWV calibration procedure.

Many times in the past I have described this method of Master Oscillator calibration on most solid state rigs that are out there today.

First off, this method does not work on ALL rigs, second, rigs that are equipped with I.F. shift feature, are much easier to use this method on. For radios that have "Pass-Band Tuning" like many ICOMs, tune the PBT for maximum low frequency response.

Here is the step by step procedure:

(1) Tune the rig to WWV, on 10.000.000 Mhz. or higher(15 or 20Mhz). Be sure that the unit display is on 10.000.000 Mhz. as close as possible, regardless of weather or not there is a "Zero-Beat".

(2)Locate the unit's Master oscillator, trimmer (for adjusting the frequency).

(3)Be sure that the rig has "warmed up" for at least 1 hour before doing this procedure.

(4)Place the rig mode, to USB or LSB.

(5)Tune the I.F. shift/PBT to the lowest frequency audio response you can get.

(6)Tune the M.O. trimmer for "zero-beat", with the lowest frequency "beat-note", that can be heard. Once the beat-note has dropped below your ear's ability to hear it, look at the S-meter, and watch the meter move slowly up and down. Your goal is to get the meter needle to stand still after you reach the lowest audio beat-note possible.

(7)Be careful not to be fooled by a higher frequency beat note, that can make the meter needle stand still. Don't be worried if you can't get the trimmer to reach absolute Zero-beat, many rigs are not able to do it, even some of the "high-end" rigs.

(8)Once you have reached Zero-Beat, or as close as you could get, recheck it after the rig has sit for about 30 minutes. When your satisfied that the unit is accurate, your done.

(9)It is very possible to reach an error factor in the M.O. of 1/4 cycle per second or less, (read visually, not heard) using my method. I have done it, so can you, with a little practice.

(10)Switch to the opposite side-band, to check that the SSB oscillators are properly aligned, if there is a large variation between side-bands (more than 50hz), the USB & LSB oscillators are out of alignment, and should be aligned according to the service manual for your unit. (Note, when switching side-bands, the zero beat method should be use again, and the IF shift will need to be tuned the opposite direction.) If the SSB oscillators needed realignment, repeat the entire procedure. This step does not apply to newer radios that are IF DSP based, no SSB adjustment is possible in these radios.

If the radio is calibrated at 15MHz for example, the frequency error in the frequency of operation will be plus on one side of the calibration frequency, and minus on the opposite when the frequency of operation is tuned from one end of the radios range to the other end. Attempts should be made to calibrate the radio at the "middle" of its range of operational coverage. This would minimize the error slew on one side or the other of the cal freq. If the user desires a greater frequency precision on a particular portion of the radio's range, the WWV calibration frequency should be closer to that part of the desired operation frequency. This will depend greatly on the MO frequency, which is not the same as the calibration frequency.

It must be understood that no matter what model of radio, there WILL be some amount of frequency error regardless of the precision of the M.O., but a precise calibration will minimize the error. Usually, this error is very small.

For new radios, a check of calibration is usually all that is required (don't be surprised if you new radio is off slightly). As the radio ages, the calibration should be checked every 3-5 years. All quartz based oscillators age and change frequency, so checking and minor adjustments will keep them "spot on".

This trick was taught to me, by my Elmer, KF5MC Joe Pursley, Many thanks to him, it works beautifully.