[sdiy] 90-degree phase displacement network calculations

Bernard Arthur Hutchins, Jr bah13 at cornell.edu
Wed Jan 13 01:34:23 CET 2021

David –

The filter design problem addressed by Parks-McClellan (etc.) is not the Chebyshev problem, but rather a digital FIR version of the analog CAUER filter (sometimes called an elliptic filter); being “Chebyshev” in both the passband and the stopband (also allowing “transition bands”).  Please do read my “A New Simplified Equiripple Design Algorithm for FIR Filters” Electronotes 175 August 1989, pp 3-50.   The approximation (to a desired response) involves the same math whether you are talking amplitude response or phase error or whatever.

I understand what you did and for the third time state that there is nothing wrong with what you did.

But you have avoided my repeated questions about what the error plot looks like if you do fewer iterations.  [ Neither have you commented your program or (despite saying there were several errors along the way) provided a full corrected copy. ]


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