[HomeBrew] notch filter

[Loren Moline WA7SKT]

Richard,

I have built a few notch filters for 75 ohms that work great. I have 2 types 
of filters I have built. They could probably be scaled for any impedance.

Loren



Not my plan but his plan for my life is my guide!
Loren Moline WA7SKT  CN86cx
Member: ARRL, Pacific Northwest VHF Society #151





>From: "Richard Blackman" <richard.blackman at sympatico.ca>
>To: "HOMEBREW" <homebrew at mailman.qth.net>
>Subject: [HomeBrew] notch filter
>Date: Mon, 29 May 2006 22:00:59 -0400
>
>** Please do NOT cross-post messages when posting to HOMEBREW **
>
>Hello to group.
>I am trying to build a 72 MHz notch filter.
>
>I  have used the ELSIE software from  Tonne Software, the free demo student 
>edition.
>It is a butterworth T shaped filter.
>pole 1 is 2.5 nH in parallel with a 1900 pF cap
>pole 2 is 2.4 uH in series with a 2 pF cap
>pole 3 is 2.5 nH in parallel with a 1900 pF cap.
>
>The plotted  shape , and tabulated values for transmittion give over -30 dB 
>at 72 Mhz.
>The problem is that it does not appear to be working, all it does is 
>slightly attenuate all frequencies applied to it. I built the filter on 
>single sided copper board, and cut out pads with a dremel tool for ugly 
>type construction on the copper side. The components are very tightly 
>grouped. I wonder if each pole should be farther apart and isolated with 
>metal dividers. Do you feel that the closeness of the components, 
>especially the inductors, is causing bleed through and loss of attenuation? 
>Or am I way off base in my troubleshooting? The second pole uses a trimmer 
>cap and a trimmer inductor. varying either has absolutely no effect in 
>notching out a 72 Mhz signal from my homebrew 72 Mhz local oscillator.
>
>Any ideas on how to improve, or should I take a completely different 
>approach?
>
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