[TowerTalk] Are All Low-Pass Filters Alike?

[Jim Lux]

At 12:11 AM 8/16/2005, Peter Chadwick wrote:
>I agree with Jim, K9YC. It's impossible to determine the real differences
>between them. A Cauer Chebycheff can be usefully arranged to have notches at
>harmonics of the various bands, but it doesn't say so.
>
>What it does say is pretty well pure BS.
>
>73
>
>Peter G3RZP
And, one of the problems with filters with zeros like Cauer (aka Elliptic) 
is that they tend to be a bit more picky about component values, especially 
when picking notch frequencies.  Most ham oriented products are hardly 
precision devices with 0.00001% components, and also are often operated 
over wide temperature ranges (which changes the component values) and with 
terminating impedances that are hardly 50 ohms (particularly out of band).

It would be quite revealing, I suspect, if ARRL or the mfr were to publish 
some test results on filters operating into a typical mistermination (say a 
dipole cut for one band).  You might find that the attenuation isn't 
anywhere near what it is with nice 50 ohm terminations, particularly if the 
filter doesn't have a lot of sections.

Jim, W6RMK