Hi all,
I'm chiming in a bit late on this topic, as I have been away from the
home QTH and the computer for a few weeks. I own an Omni VI and often
peruse the manual. Much of the confusion on this topic is due to
semantics. If we agree to the definitions of terms the confusion will go
away.
If we agree that the term "offset" means the difference in our CW
transmit frequency from the frequency of a received signal that is zero
beat to our sidetone, then a properly adjusted Omni VI has ZERO offset,
and that offset is NOT adjustable from the front panel ( RIT and XIT
turned off). By properly adjusted, I mean that the BFO frequencies and
the master reference oscillator are all adjusted by the book. The radio
equipment "offset" is zero regardless of the sidetone setting, which is
adjustable. When using narrow filters (in the 9 MHz IF) the sidetone
frequency has to be set to the difference between the filter center
frequency and the CW and LSB BFO frequency (which is 9.000 MHz) in order
to hear signals that are zero beat with the sidetone.
If the sidetone is not set as described above, you can OPERATE "offset",
listening to signals not zero beat to your sidetone and transmitting on
a slightly different frequency than the signal you listen to. In this
case the radio equipment offset is still zero, it is the operator that
is listening offset from his transmit frequency.
If you were to adjust C10 and/or C16 ( the CW TX and CW/LSB RX BFO
trimmers) on the TX AUDIO BOARD differently than "by the book", you
could make the radio have a non-zero offset. In that case the frequency
display would be incorrect for transmit, receive or both, depending on
how you misadjust them.
When using a very narrow filter in the 9 MHz IF, the PBT adjustment is
of very little utility, as the 6.3 MHz IF where the PBT works is AFTER
the 9 MHz IF, where the received audio frequency note and bandwidth has
already been determined by the narrow filter's center frequency and
bandwidth.
Dead horse now sufficiently flogged.
DE N6KB
Fraser Robertson wrote:
> Hi all, sorry if I've caused or added any confusion. I appreciate that the
> sidetone pitch is front panel adjustable, and we're told that the TX offset
> tracks that (sorry I'd forgotten that, I need to check the manual).
>
> The point I intended to make was that when our club bought its used Omni6+,
> the CW netting (offset) was way out of line with the sidetone pitch (from
> memory worse than 500Hz off). This was corrected by adjustment of a trimmer
> capacitor (on the TX AF board, top rear of rig).
>
> Regarding filter pitch, I find there is plenty of adjustment to listen at a
> low pitch if desired, by adjustment of the PBT. We did have one of the
> specially made low pitch filters, but it would not cascade with the standard
> offset filters.
>
> 73 Fraser G4BJM
>
>
>
>> From: "Roy" <royanjoy@ncn.net>
>> Reply-To: Discussion of Ten-Tec Equipment <tentec@contesting.com>
>> To: "Discussion of Ten-Tec Equipment" <tentec@contesting.com>
>> Subject: Re: [TenTec] OMNI-6+ cw offset adjustment
>> Date: Sun, 1 Jul 2007 09:56:52 -0500
>>
>> Was stated,
>>
>> "The CW offset is fixed, but is adjustable with a trimmer capacitor inside.
>> Regarding filters, I find...(etc.)"
>>
>> No, the cw offset is programmable.
>>
>> 73, Roy K6XK
>>
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>
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