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@reagan.com>
To: "Discussion of Ten-Tec Equipment" <tentec@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@earthlink.net>
Sent: Sunday, October 19, 2014 5:38pm
To: "'Discussion of Ten-Tec Equipment'" <tentec@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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