[RFI] DSL Filter Update

Roger Parsons ve3zi at yahoo.com
Sat Mar 7 21:11:39 PST 2009

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 performance.

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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