[TenTec] 3.1 KHz IF Filter for 2nd IF in Omni 6

Sun Jan 10 09:58:24 EST 2016

Gary, you REALLY need to go to omni6.wikidot.com and read the audio info
there

73, Barry N1EU

On Jan 10, 2016 1:18 AM, "Gary J FollettDukes HiFi" <dukeshifi at comcast.net>
wrote:
>
> It would seem to me that the best use of the Inroad wide filter would be
to leave the original filter in position one in the first IF. The you could
easily move a few wires to bypass that filter in receive, and go directly
to the 2l.8 KHz filter in position 2. This is easy because, in the Omni 6,
TenTec cascaded the first filter into the second one. If you use the PIN
diodes to go around the position one filter (2.4 KHz) you would take full
advantage of the wider filter in position two only in receive. In transmit,
everything would remain stock.
>
> Omni 6 radios never sounded all that bad in transmit, only in receive
(tony ears anyway). The above method should improve that sound by quite a
bit.
>
> BTW: I never observed any significant improvement in Omni 6 audio on
receive with the so-called audio improvement mod. I have tried it on
several Omni 6’s and never saw much difference.
>
> I believe the filters in the Omni 6 have more in band ripple than they
should, and also the positioning of the first OF filter with respect to the
second IF filter combine to produce the nasal sound of the omni 6
(non-optimal overlap). No amount of audio chain alteration will correct for
that.
>
> I have even taken the audio directly from the product detector and passed
this through to an outboard audio amplifier. No real improvement in audio
was observed.
>
> This supports the notion that the restricted audio arises in the IF
combination of filters and their respective center frequencies and overlap.
>
> The only other p=lace where such restricted frequency response could take
place is in the very first ceramic filter that is used prior to any of the
9 MHz roofing filters. I have never tried bypassing this just to see what
impact it has on the audio response. I will wait for that until I see hows
the filter arrangement in this particular Omni 6+ sounds.
>
>
> I can’t wait to hear how this Omni sounds tomorrow with the high buck 3.1
KHz filters in both IF’s. I have high hopes...
>
> Gary
>
>
>
>
> > On Jan 9, 2016, at 10:58 PM, elespe at lisco.com wrote:
> >
> > That is why I asked.
> > I have the 2.8khz INRAD filter and the radio sounds fantastic and gets
> > great audio reports but keeping the carrier supression better than 34 db
> > on both sidebands is impossible without moving the bfo which, without
> > doing the math on the entire radio frequency scheme, seems to have a
> > trickle down effect on screwing something else up along the way.  If the
> > bfo is wrong doesn't that reflect in the readout as well?
> > I love the INRAD "wide" filters but am going to change the 1st if down
to
> > a 2.4khz model to keep everything else in check.
> > Along the line of sounds great I somehow stumbled across a speaker that
> > fits the original hardware and hole and actually makes the OMNI VI sound
> > better than any external speaker system I have tried on it. Just dumb
luck
> > and Parts Express---who would know.
> > Paul K0UYA
> >
> >> As I recall, when one purchased the Inroad â€œwideâ€  SSB filter for
the
> >> first IF, one needed to adjust the BFO frequencies in order to get
proper
> >> positioning of the carrier on the filter slope. I do not (yet) know the
> >> adjustment range for the BFOâ€™s bu I am guessing that the BFO
adjustments
> >> in this one must have pushed that frequency another 300 Hz, or the BFO
> >> crystal(s) were changed out.
> >>
> >> Anyone who had spent $1000 to have custom filters made up would
certainly
> >> have taken proper measures to ensure that transmitted SSB was properly
> >> generated.
> >>
> >> I should know the answer tomorrow.
> >>
> >> I have not looked yet, but it is POSSIBLE that the radio may have been
> >> rewired to route the TX 9 mHz IF signal through the position 2 filter.
> >> That is a lot easier to do the one might think, due to the use of diode
> >> switching to select the desired filter, so it is possible.
> >>
> >> The first IF filter that was in the position 2 is marked â€œ48074â€
and
> >> the second IF filter in position 2 is marked 48058.
> >>
> >> Can anyone tell me if these are the numbers for the â€œstockâ€  SSB
> >> filters?
> >>
> >> I can measure them fairly easily for bandpass but it would save some
time
> >> if anyone simply knew the answer to that.
> >>
> >> I will, however, put a frequency counter on the BFO tomorrow and
measure
> >> the frequencies on LSB and USB to determine what was done to make this
> >> work. As you know, without adjustment of the BFO down the filter edge,
> >> both carrier suppression and SSB suppression would suffer quite a lot.
> >>
> >> Gary
> >>> On Jan 9, 2016, at 9:54 PM, Paul Kraemer <elespe at lisco.com <mailto:
elespe at lisco.com>> wrote:
> >>>
> >>> How is that possible?
> >>> The lsb and usb bfo frequencies are only 3khz apart
> >>> Paul K0UYA
> >>>
> >>> -----Original Message----- From: Gary J FollettDukes HiFi
> >>> Sent: Saturday, January 09, 2016 9:05 PM
> >>> To: Discussion of Ten-Tec Equipment
> >>> Subject: Re: [TenTec] 3.1 KHz IF Filter for 2nd IF in Omni 6
> >>>
> >>> I bit the bullet and took the entire bottom cover off.
> >>>
> >>> I found that there is also a custom 3.1 KHz filter in the number 1
> >>> position in the first IF (9 MHz)! This is also an 8 pole filter with
the
> >>> IF cans on board to tailor response. It is equally well made as the
> >>> second IF filter is well made.
> >>>
> >>> Iâ€™ll report tomorrow on how the radio sounds with quiet band
> >>> conditions and also get a transmitted SSB audio report. I may have
found
> >>> the Omni 6 of my dreams!
> >>>
> >>> I have always hated the SSB sound of the omni 6 (all variations).
> >>>
> >>> I contacted the fellow from whom I got this and he informed me that
the
> >>> original owner of this radio had these filters custom made for a cost
of
> >>> over $1000. I sill do not know what company made them but they are top
> >>> quality all the way.
> >>>
> >>> Apparently that fellow hated the sound of the Omni 6 as much as I
doubt
> >>> had the resources to take corrective action.
> >>>
> >>> Hopefully these filters will offer some relief as the overall design
of
> >>> the Omni 6 is one of my favorites over any other radio design.
> >>>
> >>> Itâ€™s also on of the prettiest radios going.
> >>>
> >>> Gary
> >>>
> >>>
> >>>
> >>>> On Jan 9, 2016, at 8:17 PM, Mark S. Holden <mark at holden-insurance.com
>
> >>>> wrote:
> >>>>
> >>>> On 1/9/2016 8:32 PM, Gary J FollettDukes HiFi wrote:
> >>>>> I have a 3.1 KHz bandwidth filter in one of my Omni 6+ radios. It
fits
> >>>>> perfectly into the TenTec socket and was obviously made for the en
> >>>>> Tec. However, it looks unlike any filter I havee ever seen in ANY
Ten
> >>>>> Tec product.
> >>>>>
> >>>>> It is an 8 pole filter but it also had four small IF transformers on
> >>>>> it, presumably to tailor the passband shape.
> >>>>>
> >>>>> Has anyone heard of this filter? Does any know who made it? It is
too
> >>>>> perfect to have been a home brew job. It is built on thicker board
> >>>>> stock than that used for most Ten Tec filters.
> >>>>>
> >>>>> I would assume that its intent is to improve received audio in SSB.
I
> >>>>> am going to try it in a few minutes to see what the radio sounds
like
> >>>>> compared with the others.
> >>>>>
> >>>>> Gary
> >>>>> _______________________________________________
> >>>>> TenTec mailing list
> >>>>> TenTec at contesting.com
> >>>>> http://lists.contesting.com/mailman/listinfo/tentec
> >>>>>
> >>>>>
> >>>> I'd expect that to be a fun filter for rag chewing.
> >>>>
> >>>> My Harris RF-550 rx has a 3.24khz crystal filter that's incredible
for
> >>>> SWL.  I also installed some crystal filters intended for the Racal
> >>>> 6790gm in my AOR 7030+
> >>>> _______________________________________________
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> >>>
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> >>
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> >>
> >
> >
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