I suspect that you may have a defective filter. The fact that you had to
pad an oscillator is a clue. Or maybe a BFO crystal is out of tolerance.
I measured the audio frequency response of my Omni VI Plus using the
sinewave/power method. Once I did this, I was able to see the shape of the
filter and take into account the group delay which affects the "sound" of
the radio. I didn't do a squarewave response however. I also confirmed
that the DSP artifacts were present in the RX signal regardless of the NR or
Auto Notch usage.
I've found that the mechanical Collins filters used in the Omni VII offer an
significantly enhanced signal on SSB both in transmit and receive. They are
clearly different than crystal filters regardless if they are ladder of
lattice configuration.
73
Bob K4TAX
----- Original Message -----
From: "Fraser Robertson" <g4bjm@hotmail.com>
To: "Discussion of Ten-Tec Equipment" <tentec@contesting.com>
Sent: Tuesday, March 18, 2008 6:20 PM
Subject: Re: [TenTec] Omni VI Plus audio
>
> Thanks Bob, yes I'm referring to the TX signal, although RX is similar of
> course. I agree with what you say, although the Omni6+ SSB filter is
> worse than that in any other rig I've used. I did align the oscillators
> as per the manual, in fact I had to pad one of them as there wasn't enough
> adjustment range. I rarely use SSB myself so will let someone else worry
> about it! 73 Fraser> From: RMcGraw@Blomand.net> To:
> tentec@contesting.com> Date: Mon, 17 Mar 2008 20:02:33 -0500> Subject: Re:
> [TenTec] Omni VI Plus audio> > Typical of filters, the shape factor or
> each side of the slope as measured > from the -3 dB points is typically
> not identical although we'd like to think > they are and wish they were.
> Thus a modulated carrier placed on the side of > the slope, at say the -3
> dB points, will sound different when listening to > USB or LSB output
> products of the filter. It is not a common failing, it is > a law of
> economical filter design and selection of filters that have a > rea
> sonable or tolerable amount of insertion loss as well as a host of other >
> factors such as ripple across the top, phase shift, group delay and etc.>
> > I do not discount that fact that a crystal component within the filter
> may > fail or may change frequency such that, in either case, the shape
> factor of > the filter changes. If you have means to measure the filter
> and its skirts > and insertion loss then you might find a clue as to why
> it sounds different > on USB and LSB. Otherwise, invest in a new filter
> and then complete an > alignment of the BFO oscillators. It is important
> that the alignment be > carried out in the exact sequence as described in
> the manual. There is > interaction between the adjustments. Even the FSK
> adjustments need to be > made although you may never intend to operate
> FSK.> > I trust you are speaking of transmit signal sounding different an
> not > receive signal sounding different. For receive signal sounding
> different > that may be caused by and additi
> onal factor being mis-alignment of the > PassBand tuning oscillator.> >
> 73> Bob, K4TAX> > ----- Original Message ----- > From: "Fraser Robertson"
> <g4bjm@hotmail.com>> To: <ken.d.brown@hawaiiantel.net>; "Discussion of
> Ten-Tec Equipment" > <tentec@contesting.com>> Sent: Monday, March 17, 2008
> 6:49 PM> Subject: Re: [TenTec] Omni VI Plus audio> > > >> > Our club's
> Omni6+ option3 sounds very different on USB and LSB, and it's > > not
> possible to correct it by adjusting the BFO frequencies, so it must be > >
> down to the filter being asymetrical. I understood that was a common > >
> failing, but perhaps our filter is faulty?> >> > 73 Fraser G4BJM> >> Date:
> Sun, 16 Mar 2008 18:37:51 -1000> From: ken.d.brown@hawaiiantel.net> > >>
> To: tentec@contesting.com> Subject: Re: [TenTec] Omni VI Plus audio> > > >
> >> > Now I don't know why the higher bands are different on your rig.> > >
> >> Wonder if you have an antenna problem? > >> > > If the SSB Receive (or
> > >> transmit) audio sounds differen
> t on 10, 15, 20 > meters than it does on > >> 40, 75 meters, you should be
> comparing the sound > on USB versus LSB. > >> Your SSB audio
> characteristic should not change at > all due to changing > >> bands,
> other than because of the convention of using > USB above 9 MHz > >> and
> LSB below 9 MHz. The audio characteristics also > should not change > >>
> very much from USB to LSB. If it does change, that is > an indication > >>
> that your BFO frequencies are misaligned for one or both > SSB modes. > >>
> Another possibility, although not nearly as likely, is a > partially > >>
> failed crystal filter with a non-symmetrical passband shape. > The first >
> >> thing to do is check the BFO frequencies. If you install new> > >
> filters, of any brand, without getting the BFO frequencies right, you > >
> > will still have a problem.> > DE N6KB> > > >
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