It all depends on a lot of things.
For one thing there are filter loss compensation jumpers in the Omni VI,
but I think those are only for the 9 MHz filters, not for the 6.3 MHz IF
filters.
The other thing that really matters is the spectral distribution of the
noise and signal power within the filter bandpass. For example if the power
of the noise or the signal is distributed uniformly across the whole 2.4
kHz bandwidth of the filter, then it would be perfectly normal for the S
meter reading to drop by a factor of 1.8 / 2.4 when switching from the 2.4
kHz filter to the 1.8 kHz filter. On the other hand, if you had a narrow
band signal like a CW signal centered in the bandpass of both filters,
which was the dominant contributor to the S meter reading, then the S meter
reading should not change when switching between those two filters, unless
the filters have significantly different losses.
The S meter responds to the total power in the whole bandpass of the IF.
When you reduce the bandwidth, all other things being equal and with a
uniform power distribution (white noise) then the total power is
proportional to the bandwidth. So the S meter should drop with narrower
filters. But with a non-uniform power distribution, such as a single tone
CW signal which has the power concentrated in a small fraction of the total
filter bandwidth, you would expect no change in S meter reading when going
to narrower filters, provided you keep the signal inside the filter
bandwidth.
DE N6KB
On Sun, Aug 6, 2017 at 4:12 PM, Stan Gammons <s_gammons@charter.net> wrote:
> Hi everyone,
>
> After adjusting the BFO and TCXO and using the Omni VI for SSB and digital
> modes for a little over a week now, I kind of like the new to me rig. I
> noticed a +2 or so S unit change when switching from the 2.4 Kc filter to
> the 1.8 Kc filter. It's like there is less loss or more gain when
> switching to the 1.8 Kc filter. I wouldn't think that would be "normal"
> Switching to the .5 Kc filter doesn't do that. S meter reading is the same
> as the 2.4 Kc filter. Anyone seen this before?
>
>
> 73
>
> Stan
> KM4HQE
>
>
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