[HomeBrew] notch filter

[Steven Weber]

>Hello to group.
>I am trying to build a 72 MHz notch filter.
>
>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.
>

I plugged those values into NOVA-586 and it gave me a notch of only -0.2
dB! (I'm assuming 50 ohm termination) 

Something didn't look right with the magnitude of those values. The poles
need to resonate at the notch frequency and those values seemed way off for
72 MHz. 

Then I changed the values to 190 p || 25 nH
and 240  nH in series with 20 p 
and got a nice - 40 dB notch about where you want it. 
So I think you got the decimal point wrong in all the values.

For best results, you should put a shield between the tuned circuits. You
need a magnetic shield, so use tin. 

72,
Steve, KD1JV
"Melt Solder"
White Mountains of New Hampshire
http://www.qsl.net/kd1jv/
http://kd1jv.qrpradio.com