[TenTec] Omni VI Mystery

Bob McGraw - K4TAX RMcGraw at Blomand.net
Wed Jul 30 10:27:17 EDT 2014 

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 at gmail.com>
To: "Discussion of Ten-Tec Equipment" <tentec at 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 at 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 at gmail.com>
>>
>> To: "Discussion of Ten-Tec Equipment" <tentec at 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 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
>>>> _______________________________________________
>>>> TenTec mailing list
>>>> TenTec at contesting.com
>>>> http://lists.contesting.com/mailman/listinfo/tentec
>>>>
>>>>  _______________________________________________
>>> TenTec mailing list
>>> TenTec at contesting.com
>>> http://lists.contesting.com/mailman/listinfo/tentec
>>>
>>>
>>
>> _______________________________________________
>> TenTec mailing list
>> TenTec at contesting.com
>> http://lists.contesting.com/mailman/listinfo/tentec
>>
> _______________________________________________
> TenTec mailing list
> TenTec at contesting.com
> http://lists.contesting.com/mailman/listinfo/tentec
>

More information about the TenTec mailing list