You're correct, and I apologize. In fact, the example I gave of a
"quarter wave" filter contradicts the statement about the attenuation. I
was thinking of a Butterworth when I wrote it, but as you point out and
as my own example shows, there are many other types for which the
statement is wrong.

I apologize for the error. Thanks for the correction.

Roy Lewallen, W7EL

Peter O. Brackett wrote:

Roy:
[snip]

The last sentence should read:

A lossless lowpass filter has zero attenuation only at DC.

:
:

Roy Lewallen, W7EL


Ummmm... no that statement is only true for one type of approximation
polynomial.

. . .