The frequency has to be resolved to 1 Hz or better per Ten-Tec info. This
BFO along with the HF osc and VFO all have a relationship with regard to the
final frequency received or transmitted. Any error at any of these makes
things worse. I've always practiced that the final frequency resolution
should be done by an instrument capable of an accuracy of 1/10 the final
value. Hence to resolve to 1 Hz a resolution of 0.1 Hz is required.
Personally I notice a lot and I mean a lot of CW and digital QSO's that are
apparently not on the same frequency. Although not of recent repairs,
previously I did find that many, and I reference other brands, where the
transmit frequency and receive frequency are not the same. In some cases
the difference may be 1 or 2 Hz but in some the error may be 5 to 10 Hz.
With AFC on digital programs running, and two stations in QSO and a 5 Hz
shift on one, each transmission they will leap frog up or down the band by
that amount. A QSO with 20 transmissions will then move some 20 to 50 Hz.
With the newer digital displays capable of showing a frequency to 1 Hz, then
hams expect them to be accurate to 1 Hz., because that's what the display
shows. Our radios today are good, but they are not precise frequency
determining equipment. As I've stated before, "the strength of a chain is
defined by its weakest link".
It is just a matter of how precise we desire to be.
73
Bob, K4TAX
----- Original Message -----
From: "Barry N1EU" <barry.n1eu@gmail.com>
To: "Discussion of Ten-Tec Equipment" <tentec@contesting.com>
Sent: Wednesday, July 30, 2014 8:33 AM
Subject: Re: [TenTec] Omni VI Mystery
Why does a BFO oscillator need 0.1Hz accuracy?
Barry N1EU
On Wed, Jul 30, 2014 at 1:30 PM, Bob McGraw - K4TAX <RMcGraw@blomand.net>
wrote:
Sorry I can't agree that using a receiver would be adequate for
alignment.
My experience in repairing Paragon and Omni VI radios, a frequency
counter
with an accuracy of 0.1 Hz or better is required for the BFO adjustments.
For proper alignment, one must follow the steps in exact sequence as
listed
in the manual under the section TX Audio.
There is interaction between the alignment steps and I always go through
the steps in sequence at least 2 or 3 times before completion. This
includes the CW, LSB, USB and FSK Space and FSK Mark modes. In
performing
the alignment procedure one will likely find the BFO switching is not
taking place thus providing the transmitter off-set thus the true reason
for the fault.
Although I no longer do repair work, except for my self, I have referred
this to a person that does repair Paragon and Omni VI radios. He is not
associated with Tentec.
73
Bob, K4TAX
----- Original Message ----- From: "Barry N1EU" <barry.n1eu@gmail.com>
To: "Discussion of Ten-Tec Equipment" <tentec@contesting.com>
Sent: Wednesday, July 30, 2014 6:18 AM
Subject: Re: [TenTec] Omni VI Mystery
Instead of a freq counter, you can use a general coverage receiver with
fairly precise digital readout. I've used a K3 and Orion subrx for this
purpose. The Omni 6 BFO test point level is low enough to feed directly
into the rx antenna input through a capacitor.
Back on day 1, I encouraged you to check your BFO oscillator alignment.
Barry N1EU
On Wed, Jul 30, 2014 at 1:43 AM, Jim Allen <jim.allen@longhornband.net>
wrote:
Some will remember the thread a few months back in which I described
the
problem I had been having making contacts with the Omni VI opt 3 I
have.
I
realized there was a problem with the radio when I used my 706MKIIG at
5
watts one day in a QSO party with the same antenna and made contacts
all
over the place no problem.
It turns out the radio is off somehow by about the amount of the
sidetone,
so when I zero beat a CW station (match tone set in sidetone) and
transmit,
the other station hears no tone. My signal is below his audible range
and/or outside his passband.
We did some testing here between the 706, the Omni and other stations
and
determined that the problem could be gotten around by setting the XIT
on
to
-whatever the sidetone was, in my case, usually 700Hz. That made the
radio
work, except for the transmit frequency being off, and hopping around
with
QSK, but it put my signal at the frequency that other stations would
hear
it.
I was not content to leave it like that so sent it to TenTec to check
the
alignment and/or correct whatever was occurring to cause this. To my
chagrin, Paul reported that the radio was just fine, working as
designed,
no problems, aligned just fine working per factory spec, nothing
needed,
etc., and sent it back. At least he didn't charge me for this.
About that time, I found a Omni VI+, with full filters and
speaker/power
supply at a price that I found attractive, so I bought it. I've been
using
it for more than a month, works great, just the way you expect, and
have
no
trouble making contracts, in the context of a 100 watt radio with a
so-so
antenna anyway. I used it for Field Day at 5 watts output to a
homebrew
S9v31 vertical and was very pleased with the performance, given the
circumstances.
This Omni VI still bugs me though, so I set up all three radios and did
some testing. I set all three radios on 14.030, using the no output on
the
two Omnis and a dummy load on the 706. When I transmit using the 706,
I
hear that signal on 14.030 in the Omni VI+, and at 14.030.4 zerobeat on
the
Omni VI, in both cases matching the tone using that function on the CW
button. Both sidetones are set at 700Hz.
When I set the Omni VI to 14.030 and transmit, I zero that on the Omni
VI+
at 14.030.04, a 40 Hz difference. On the 706, I zero the signal at
14.030.07. There is a slight difference in the calibration of these 3
radios, and they sometimes vary 10 Hz or so anyway.
When I hear the Omni VI+ and zerobeat that signal in the Omni VI, it is
at
14.030.42. In a QSO, I would hear the Omni VI+ calling and zero that
signal. When I called using the Omni VI, on the zero frequency, I hear
it
in the VI+ as a very low pitch, almost a buzz. When I turn on XIT, at
-700Hz and call, the Omni VI+ hears it with a higher audio tone, and
zeros
the Omni VI signal at 14.029.79.
It looks to me like perhaps the Omni VI is off calibration slightly,
but
that doesn't explain why it doesn't transmit with the proper offset as
expected, without XIT being on anyway.
I tried a QSO with these three radios. I call CQ using the 706, I
"hear"
and zero that signal on the Omni + at 14.030, the same as the 706. I
reply
using the Omni VI+ and hear the reply in the 706, with a ~700 hz. tone.
I
hear and zero the same signal from the 706 using the Omni VI, at
14.030.39. When I reply to the 706, the 706 hears a strong signal at a
very low audio tone, inaudible. When I click XIT -7 on the Omni VI, I
hear
it in the 706 just fine.
I have consulted off list with a very clever and exceedingly
knowledgeable
Tentec user, who probably wishes to remain anonymous, and he has
suggested
I check the alignment myself. This fellow also suggested a way to
determine if one or more of the parts in the affected circuit have gone
bad. I do not have a frequency counter, and do not know where to
obtain
access to one. What kind of frequency counter ought to be used for
this?
Is there anyone who works on these radios, other than Tentec, who has
the
test gear etc to resolve this?
There has to be an explanation why the VI doesn't work like the VI+ in
this
respect.
TIA
73 de W6OGC Jim Allen
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