[Premium-Rx] Filter phase response

[John Reed]

----- Original Message -----
From: "George Georgevits" <georgg at bigpond.net.au>
To: "Premium-RX LIST" <premium-rx at ml.skirrow.org>
Sent: Tuesday, October 07, 2003 4:33 PM
Subject: RE: [Premium-Rx] Marconi LP Filter


> Interesting that no-one has mentioned the IF filter group delay or PHASE
> RESPONSE!
>
> I think you will find this is responsible for many of the effects
described
> qualitatively by others here. For example, the amount of ringing exhibited
> by a filter is a function of its phase response. When a receiver is used
for
> data reception, linear phase response (ie. flat group delay) is what it is
> all about.

Check out this web page from the Lowdown:

http://www.lwca.org/library/articles/jtreed/impr/impr1.htm

This article compares a digital, linear phase 100 Hz filter in a W-J HF-1000
with a 100 Hz crystal filter from an old surplus receiver.  Take a look at
these two impulse responses and see if you think linear phase is the answer
to ringing problems.

John Reed