[Elecraft] Filter Cascade Effect

[Bill W4ZV]

Jim Brown-10 wrote:
> 
> 
> Right on!  BUT -- one good way to deal with this when you already own the 
> narrower filter is to tell the K3 that its bandwidth is wider than it is.
> For 
> example, I have tell the K3 my 400 Hz 8 pole filter is 500 Hz, and the 1.8 
> kHz filter is 2.2 kHz. I find that I also want to shift the 1.8 kHz filter 
> down about 150 Hz. 
> 

        Been there and done that...

DSP    Measured     Cascaded (with 549 Hz XFIL)

500     482           432
600     522           426  (my usual setting...real but anomalous result)
700     608           457
800     700           492
1000    890          526 

As Ed W0YK said, you can get away with a *little* of this but I can assure
you there are very serious consequences if you tried to use DSP 1000 above
to stretch the 549 Hz XFIL to it's full BW (and even then you only get to
526).  I don't want to elaborate but speak from personal experience!

The real solution IMHO is about a 750 Hz XFIL which will net about 600 Hz
when cascaded with the DSP.  I had a 1k and got rid of it because it's
simply too wide for serious contest use where it will typically span
200-1200 Hz at normal PITCH settings.  For example, if you have 450 Hz PITCH
set, that S9+30 guy 500 Hz up (at 950 Hz) will come roaring through your 1k
XFIL and de-sense you.

As I said before, maybe the variable filters will work...or maybe Inrad will
do a 750 Hz filter.

73,  Bill

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