[hidden email] wrote:
> Use the shape factor to predict the 60 db down response or band width.
> example = the 200 Hz filter has 4 to 1 so ................... multiply
> with a calculator the 6 db response by 4 and that would equal 224 X 4 =
> 896 Hz and the 8 pole 250 Hz has a 2 X 1 so it is 270 X 2 = 740 !
>
> so the 8 pole is really 156 Hz narrower than the 200 in getting rid of
> LOUD ADJACENT QRM !
This is very misleading, because the ultimate selectivity is provided by
the DSP.
So even though there would a big difference if the selectivity were
provided only by the filters, they are only needed to protect the DSP. A
signal *within the crystal passband* has to be S9 +30 dB before it will
activate the hardware AGC; so if a signal is already on the skirt of the
crystal filter, it will have to be even louder before any desensing will
take place.
--
73,
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco_______________________________________________
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