[TenTec] OMNI-VI question

Sun Oct 19 22:44:50 EDT 2014

All this sounds good and so easy to do, however  we are dealing with an Omni 
VI which may have an oven oscillator that may or may not heat correctly and 
does take time to warm up and does drift with temperature as much as 100 Hz 
or so.  Or perhaps a later model Omni VI that does have a TCXO for the 
reference.  Plus the BFO oscillators that are crystals, not TCXO's nor oven 
controlled nor are they locked to the master oscillator.  The same is true 
for the Paragon series.

I presently have an Omni VI Plus on the bench for service and it does have 
the later TCXO.  I'll measure it tomorrow, normalize the error and let you 
know the results on every band.  We all may be surprised.

For those that choose to use WWV, as we've done for years and while this is 
a good reference of known frequency, it only allows one to check accuracy or 
calibration on the specific band i.e 30 meters or 10 MHz.  What about the 
other bands 160M, 80M,40M and such?  For me I must start by knowing the 
frequency and associated error for every band.  Take note of the fact they 
will be different.  Then find the mean frequency and adjust typically 30M 
for that error.  This keeps the errors on other bands within reason.

Typical of one model radio I recently serviced:
160M = -25Hz
80M = - 13 Hz
60M = -7 Hz
40M = -3 Hz
30M = +/-0 Hz
20M = + 2 Hz
17M = +5 Hz
15M = +7 Hz
12M = +10 Hz
10M = +20 Hz

In the above case, it would have been better to set the 30M reference to + 2 
Hz as opposed to 0 Hz.

Now if one had used the 2.5 MHz WWV and set the reference for 0 Hz on 160M, 
when they checked the radio on 10M they likely would have been found it to 
be off some 50 Hz to 60 Hz.

There is a way to normalize the errors and bring the accuracy to within 
typically +/- 10 Hz or better on all bands  I don't view how it can not be 
done with another ham receiver unless that receiver is known to have an 
error of less than 1 Hz on all bands.  This is not very likely to happen 
from my experience.

We have gotten so accustomed to setting the dial to a specific set of 
numbers and saying that is the frequency.  Well it is close, maybe close 
enough for you, but don't kid yourself,  it is likely more in actual error 
than you may realize.  If you choose to see just how good your receiver is 
with regard to frequency, try the ARRL frequency measuring test in November.

If you believe that 10 Hz to 20 Hz is close enough for your operation,  then 
so be it.  However some operators insist on being zero beat within 1 or 2 
Hz.  Thus the reason for the prescribed precision.  After all, many of our 
radios today have a frequency read-out to the 1 Hz digit.

For those that have one of the "smart phones" I suggest the free app 
Cateater Tuner. It reads out in 0.1 Hz.  Just set it next to the radio, let 
it hear the CW note and adjust the tuning for your sidetone frequency.  It 
also generates a very nice sine wave signal too.  If you use the F5 musical 
note it is 698.5 Hz.   I find the accuracy to be +/- 0.5 Hz.

73
Bob, K4TAX

----- Original Message ----- 
From: <wt4t at reagan.com>
To: "Discussion of Ten-Tec Equipment" <tentec at contesting.com>
Sent: Sunday, October 19, 2014 5:56 PM
Subject: Re: [TenTec] OMNI-VI question

> Charles
> Is a great idea to use the computer ,my problem is my shack computer is a 
> mac. not saying these programs aren't available for the mac,I have never 
> seen them. Since the VI has a coupla of other problems ,think I will sent 
> it to ten tec while they still service the VI. Like I mentioned before my 
> old test gear ,as in heath kit and eico,is not up to the task of doing 
> this tight of setup.
> thanks
> 73
> dale wt4t
> -----Original Message-----
> From: "Charles Strickland" <wa4oss at earthlink.net>
> Sent: Sunday, October 19, 2014 5:38pm
> To: "'Discussion of Ten-Tec Equipment'" <tentec at contesting.com>
> Subject: Re: [TenTec] OMNI-VI question
>
> Most of us today have test gear sitting in front of us that allows us to 
> do things that years ago was beyond our financial means.
>
> If by chance you have your pc interfaced to your rig for received audio. 
> Use one of the many free spectral analysis programs to view the 500 or 600 
> hz tones from WWV while in the am mode. With a narrow span identify the 
> tone that you choose, switch to either upper or lower sideband and rotate 
> the tuning until the tone is at the same position (frequency) as when in 
> am mode. Then using the receiver frequency display you have the error 
> amount. Adjust the reference oscillator until the tone is at the correct 
> position or frequency on the spectral display while in either upper or 
> lower sideband and the receiver is properly tune to WWV. Use the highest 
> frequency that you can receive WWV for best resolution. Be sure to keep 
> track of which tone WWV is sending.
>
> I have been able to get mine to within plus or minus 0.3 hz at 20 mhz with 
> this method. That is when compared to my rubidium standard.
>
>
>
>
>
>
>
>
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