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

[Lee]

  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
>>
>>
>>