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
reasonable 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 additional 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 different 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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