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@comcast.net>
To: "Discussion of Ten-Tec Equipment" <tentec@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@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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