On Wed, 2007-03-07 at 13:39 -0500, Bill Cotter wrote:
> Peter,
>
> I have the Inrad 763 filter (600Hz CW, 9000.7kHz IF) installed on
> the roofing filter board, Inrad 759 filter (400Hz CW, 9000.7kHz IF,
> N2) and Inrad 750 filter (400Hz CW, 6299.25kHz IF) installed in my
> OMNI-VI+. Operating on 80/40M during the early evenings is a
> particular challenge with the atmospheric noise, static crashes and
> QRM from SSB stations closing in on the CW sub-band.
>
> Operating without the roofing filter, 2.4kHz first IF and 500Hz TT
> filter, the QRN and QRM is dramatic. Activating the -20dB
> attenuator and/or reducing the RF gain reduces the overall noise
> power mentioned by Gerald below.
And it cuts down on how much the peaks of the noise spikes overload
stages.
> Switching in both 400Hz filters
> (1st and 2nd IF) plus the 600Hz roofing filter SUBSTANTIALLY
> reduces the noise on weak signals. I attribute the improvement in
> S/N ratio to the total shape factor and quality of the filters.
> And, this improvement is without using the LP/NR DSP settings, with
> their unique contribution of artifacts (ringing, popping, etc).
The more you narrow the band going into the DSP, the more you handicap
its noise reduction algorithms.
>
> For many years I used the TT dual-500Hz and TT Dual-250Hz filters,
> in spite of their passband ripple and perceived blow-by. Upon
> installation of the Inrad filters, you can immediately hear the
> improved shape factor and low PB ripple. It is startling and
> clearly obvious with the first listen.
>
> I have the same issues with diminished hearing, and the Inrad
> filter combination was a sound financial decision for the return in
> weak signal performance improvement. The reduction in fatigue from
> noise and QRM has made operating the OMNI a continuing pleasure.
>
> 73 es tnx bill n4lg
>
> PS: I have no pecuniary or other interest in INRAD other than being
> a satisfied customer.
>
--
73, Jerry, K0CQ,
All content copyright Dr. Gerald N. Johnson, electrical engineer
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