Filters and things...

Ed Kleckner
Wed, 1 May 1996 16:38:25 -0700 (PDT)

Vernon -- I'll take a stab at some of your questions, but also refer you 
to Chapter 17 of the 1995 ARRL Handbook which describes in great detail 
the operation of the Omni VI which, i think, is very similar to the Omni 
> Many of you out there had told me the virtues of running a 1.8 and .500
> filters cascaded together for CW work.  Okay, I've tried this; what is the
> advantage?  I have found myself using the .250 on crowded bands instead of
> the .500 & .500 combo.   
I usually use 500/500.  Using 500 in the 9 MHz filter has the advantage 
of keeping a lot of noise and spurious signals out of the IF 
channel...I'm not sure what the advantage of using 1.8 in the ( MHz 
channel is.
> Basicly what I am asking is this; (remember I'm a new HAM); how does the
> two filters (1st and 2nd IF) work together?  Where does the passband tuning
> fit into this picture?  Is the passband tuning in between the two IF's?  I
> have learned how to separate two signals coming thru the filters using the
> passband tuning; but how does it work? 
The 9 MHz filter is conventional, the 6.3 MHz filter has two mixers one 
at the entrance and one at the exit. They are both driven by a common 
local oscillator.  As the frequency of the LO varies, the bandpass of the 
6.3 MH filter is shifted relative the the bandpass of the 9 MHz filter, 
thus affording bandpass tuning.  On CW this is very effective if both 
filters have the same bandpass.
Hope this helps...Ed
~ Ed Kleckner, N7YQR          ~
~ ~