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Re: [RFI] DSL Filter Update

To: rfi@contesting.com
Subject: Re: [RFI] DSL Filter Update
From: Roger Parsons <ve3zi@yahoo.com>
Reply-to: ve3zi@rac.ca
Date: Sat, 7 Mar 2009 21:11:39 -0800 (PST)
List-post: <rfi@contesting.com">mailto:rfi@contesting.com>
I stand corrected about feed/load impedance and measurement of filter response. 
I should have said 'If the feed and load impedances are purely resistive and 
reasonably close to the filter design impedance then the effect will be 
negligible.' I will try to be more precise in future....

I am sure that the response of the filter in terms of phase, and to a lesser 
extent amplitude is not optimum. However, it is a very simple filter and in 
several cases it has effected a complete cure without affecting the speed of 
the DSL circuit. (In my case ~5Mb.) In pure engineering terms I am sure that a 
Bessel's function filter would be better, but it would need many more sections 
to achieve a satisfactory cut-off. Additionally, I don't believe that the 
perfect filter is possible as the DSL passband can include 160m, so that if 
protection is required on that band there must potentially be a hit on DSL 

Surely the art of good engineering (if that is not an oxymoron) is to design 
equipment that achieves the desired effect with the least possible effort. I 
think that the unknown OK station did just that.

73 Roger

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