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

Mon Jan 11 13:16:00 EST 2016

That is not mentioned in the manual but, since you say it, it must be true.

Nonetheless, I HAVE had both on the bench at the same time and the early Omni 6 did sound better than the later one, more like an Omni 5, TO MY EARS at the time.

In addition, the effect of the 3.1 filters, evaluated in a test that few if any have ever duplicated, DOES make a significant difference (improvement) in the Omni 6+ audio when the DSP is bypassed. That is irrefutable.

73

Gary

> On Jan 11, 2016, at 11:54 AM, Barry N1EU <barry.n1eu at gmail.com> wrote:
> 
> All Omni 6's from day one, whether "early", middle, or late, had audio band
> pass filtering that IS the specific culprit in what is discussed here.  It
> has nothing to do with Omni 6+ specific dsp features.
> 
> Barry N1EU
> 
> 
> On Mon, Jan 11, 2016 at 12:10 PM, Gary J FollettDukes HiFi <
> dukeshifi at comcast.net> wrote:
> 
>> Early Omni 6 radios did not have DSP noise reduction. The plain Omni 6 did
>> have an analog audio Notch Filter function via U5 on the IF/AF board.
>> 
>> The original Omni 6 did have DSP auto notch in SSB as well as programmable
>> CW offset and a CW digital lowpass filter. No mention is made of any audio
>> low pass filtering in SSB.
>> 
>> So yes, the original DID have some DSP functions but not very much (sorry
>> for saying “no DSP”, I should have said “limited DSP”). From my personal
>> listening experience, they did not do any low pass filtering of the audio
>> in SSB in the first version.
>> 
>> An early Omni 6 had a sound very similar to that of an Omni 5, to my ears.
>> Not perfectly “natural” but not terrible.
>> 
>> 73,
>> 
>> Gary
>> 
>> 
>> 
>>> On Jan 11, 2016, at 10:30 AM, Lee <lee at wa3fiy.com> wrote:
>>> 
>>> I thought all Omni VI's had DSP.   Later versions only added to or
>> modified the DSP functions.
>>> 
>>> 73,
>>> 
>>> -Lee-
>>> 
>>> WA3FIY
>>> 
>>> ------ Original Message ------
>>> From: "Gary J FollettDukes HiFi" <dukeshifi at comcast.net>
>>> To: "Discussion of Ten-Tec Equipment" <tentec at contesting.com>
>>> Sent: 1/11/2016 10:45:22 AM
>>> Subject: Re: [TenTec] 3.1 KHz IF Filter for 2nd IF in Omni 6
>>> 
>>>> I don’t disagree with the things you have said about the role of the
>> DSP in restricting the Omni 6 SSB sound. It is a major limitation.
>>>> 
>>>> However, I had experienced significant audio frequency restriction in
>> previous tests I had done with plain Omni 6 radios that had no DSP. Perhaps
>> that was the result of some of the audio filtering that was present in
>> those radios.
>>>> 
>>>> However, I believe I am probably the only person who has had access to
>> this filter pair as they were very costly one-up devices.
>>>> 
>>>> The result was that, with the DSP and all on-board audio circuitry
>> bypassed in this very late Omni 6+ that I have, the use of the 3.1 KHz
>> filters in both IF’s made a very dramatic change in the audio quality, when
>> compared against the stock 2.4 KHz filters. No amount of operating the PBT
>> with the 2.4 KHz filters in place could produce the sound quality I hear
>> with the 3.1 KHz filters.
>>>> 
>>>> In addition, Inrad does offer a 2.8 KHz filter for the Eagle and the
>> Orion 2. Neither of these passes the CW signal through the IF roofing
>> filter. Why would they offer that?
>>>> 
>>>> I  think there is a need to define the term “restricted response” in
>> terms of a ham receiver. 2.4 KHz is plenty of bandwidth for any receiver to
>> produce acceptable communications quality audio and, as you state
>> correctly, the Omni 6 (any version) provides “acceptable communications
>> quality audio” with the stock 2.4 KHz filters in place and the DSP bypassed
>> or not present). But when I set any Omni 6 beside an Orion or an Icom Pro
>> series radio, the sound from the Omni is fatiguing because it does not
>> sound natural. I’m not looking for hyper-bass, just sound that is natural
>> (to me), as close as possible to that which I would hear with the person in
>> the room with me. With the 3.1 KHz filters in place, and the DSP bypassed,
>> this Omni 6+ sounds VERY natural.
>>>> 
>>>> I have been a music audiophile for probably 40 years, and have built
>> output transformer less vacuum tube power amplifiers from scratch in order
>> to give me the sound I wanted with some significant bass (but not to
>> excess). Therefore I am pretty experienced in knowing what to look for when
>> I make changes to an audio product, which is essentially what we are
>> talking about here.
>>>> 
>>>> 73,
>>>> 
>>>> Gary
>>>> W0DVN
>>>> 
>>>> 
>>>> 
>>>>> On Jan 11, 2016, at 7:09 AM, Barry N1EU <barry.n1eu at gmail.com> wrote:
>>>>> 
>>>>> I just wanted to post a fuller follow-on comment, now that I'm no
>> longer
>>>>> dependent on a cell phone to post.
>>>>> 
>>>>> People are free to believe whatever they want to believe, but in
>> actuality,
>>>>> there is ONE and only one reason for the restricted ssb rx audio
>> passband
>>>>> in the Omni 6, assuming you don't have narrow xtal filters installed
>> and
>>>>> assuming you have the BFO oscillators properly aligned.  Actually a
>> single
>>>>> picture tells the whole story:
>>>>> http://omni6.wdfiles.com/local--files/rxaudio/o6spectra_text.jpg  -
>> with
>>>>> the dsp processor out of the signal path (top trace), the response is
>> only
>>>>> determined by the filter bandwidth.
>>>>> 
>>>>> All the Omni 6 rx audio goes through the dsp processor.  The dsp
>> processor
>>>>> has several principal functions, and you can't simply bypass it without
>>>>> there being issues.  But one obvious dsp effect is rolling off the rx
>> audio
>>>>> spectrum at the bottom and at the top, by design.  Ten-Tec designed the
>>>>> Omni 6 from the beginning to use 2400hz filters and optimized the dsp
>>>>> processing for those filters.  It only becomes an issue if you want
>> fuller
>>>>> fidelity (especially on the low end).
>>>>> 
>>>>> The Inrad 2800hz 9MHz filter was introduced NOT to improve ssb
>> fidelity,
>>>>> but to produce a better sounding cw transmit signal.  You can search
>> the
>>>>> reflector archives and find all the information from ~15 years ago.
>>>>> 
>>>>> Over the years I've done A LOT of experimentation on improving the ssb
>>>>> receive response, but it's not a simple matter.  I succeeded in the
>> end,
>>>>> but I also came to realize that the Omni 6 is essentially/inherently a
>>>>> superb cw radio (perhaps the best ever) and the Orion is the much more
>>>>> suitable radio if you want better ssb receive fidelity.
>>>>> 
>>>>> I also found that the Omni 6 carrier null level is marginal with the
>> Inrad
>>>>> 2800Hz 9MHz filter installed, even after re-aligning as Inrad
>> recommends.
>>>>> I've done this on several Omni 6's and the carrier null is shallow and
>> I've
>>>>> always thought the amount of carrier still being transmitted was
>> enough to
>>>>> make me a bit uncomfortable using the rig in ssb with that filter
>> installed.
>>>>> 
>>>>> 73, Barry N1EU
>>>>> 
>>>>> 
>>>>> 
>>> 
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