[Elecraft] Re: start without ANY extra roofing filters....

[Jack Smith]

Passband ripple is more a function of the filter design parameters--was 
it designed as a Chebyshev with 1 dB passband ripple, or a Butterworth 
with a flat passband, or a Gaussian with a rounded passband, etc. And, 
of course, those parameters govern also how fast the skirts roll off 
and, of great importance in many applications, how the group delay looks.

All else being equal (e.g., two filters, same nominal 3 dB bandwidth, 
same design parameter, e.g., Chebyshev) the one with more poles will 
have better passband roll off, or shape factor.

I can show you some four pole crystal filters I've designed and built 
with essentially perfectly flat passbands and others with lumpy passbands.

Jack K8ZOA


Fred (FL) wrote:
> If my CAD computer design days don't fail me, I recall
> 8-pole type filters - had much steeper skirts, but
> not so hot passbands, sort of ripply.  Having already
> forgotten the spec on group-delay (phase?) - I'll
> have to look that up.
>
> Fred, N3CSY
>
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