[TenTec] Omni VI Plus freq. readout

George, W5YR w5yr@att.net
Sat, 28 Sep 2002 20:04:14 -0500

Pete, when I turn on my IC-756 PRO from a cold start, it will be less than
5 Hz different from WWV. After two minutes it will be within 3 Hz of WWV.
After 5-10 minutes it will be less than  two Hz different from WWV. AT any
time after the rig has been on for several hours, the observed dial
calibration is usually 1.x Hz removed from WWV.

I measure dial calibration error by tuning in WWV at 9999.000 USB (and/.or
10,001.000 LSB) and looking at the 1000 Hz beatnote on an audio spectrum
analyzer program such as SpectroGram or a PSK31 program such as DigiPan.
DigiPan will measure the input frequency to within 0.1 Hz by centering a 15
Hz bandwidth DSP filter over the incoming signal. I have crosschecked both
programs with a professional audio spectrum analysis program costing many
$$$ in comparison. Both are right on.

I use the PRO to set up my counter since there is no guarantee that the
counter is accurate to any particular reference. I also run the counter
24/7/365 and still it needs to be touched up by a Hz or two or three

In order to verify the intergrity and accuracy of the program and of the
soundcard, I first tune in WWV on AM and measure the audio tone modulation
frequency. Invariably, this frequency will be reported as 500.0 or 600.0 or
whatever tone is being used. Then I set the dial as described above and
measure the beatnote to obtain the dial calibration error. This approach is
quick, highly accurate and does not rely upon any human sensory judgement
or action in determining the outcome, other than selecting the audio trace
with a mouse click.

Now, this experience with the PRO is exceptional in my opinion and
experience. I had a Kachina 505DSP that was seldom closer than 5 Hz even
after it performed its automatic self-calibration. My IC-765 tunes in 10 Hz
steps and is usually within 10 Hz after warming up thoroughly and can be
calibrated to within a Hz on a short-term basis.

Try the audio spectrum analyzer approach and see how you like it.

73/72, George    
Fairview, TX 30 mi NE of Dallas in Collin county EM13qe   
Amateur Radio W5YR -  the Yellow Rose of Texas
In the 57th year and it just keeps getting better!

AC5E@aol.com wrote:
> Except for a few rigs with a built in frequency counter, I haven't found ANY
> rig that's on its indicated frequency. Most rigs are within 7-10 ppm, a few
> have been within 2-3 ppm, but they have all been more or less "off."
> I don't have a "professional" counter but my ears say the crystal calibrator
> is within 2 Hz of WWV at 10 mHz, the B&K I do have says the calibrator is
> dead on, and that all three of my VI's, one plus and two option 3's, are rock
> solid and within perhaps 30 Hz of the indicated transmit frequency.
> Of course, besides the direct method of transmitting and checking the
> frequency, you can hook a counter up to the speaker, tune in WWV in CW mode,
> and check the audio frequency over time. This is a pretty solid check of
> receive frequency stability as well.
> I sure wish Izzy had gone some other way. I'd be at the 'fest.