[TenTec] Omni VI Mystery

Barry N1EU barry.n1eu at gmail.com
Wed Jul 30 07:18:05 EDT 2014


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 at 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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