Yes, I understand now. That seems like a great system for attenuating 2nd
harmonics. Its equivalent circuit (assuning lossless coax) resembles a pi
filter. At the second harmonic, the input and output parallel branches
(stubs) would approximate short circuits, and the series branch would
approximate an open circuit. Thanks for the great idea.
73,
Riki, K7NJ - 4X4NJ
-----Original Message-----
From: cq-contest-bounces@contesting.com
[mailto:cq-contest-bounces@contesting.com]On Behalf Of W0UN -- John
Brosnahan
Sent: Friday, June 11, 2004 12:58 PM
To: R. Kline; cq-contest@contesting.com
Subject: RE: [CQ-Contest] Bandpass filters for M/S or M/M environment
At 09:05 AM 6/11/2004, R. Kline wrote:
>I agree in principle. However the 30-40 dB attenuation expected appears
>somehwhat exaggerated from my personal experience and from what I've read.
>Perhaps there is a more involved system of stubs that will do this (other
>than a simple short circuited quarter wave stub in parallel with the
>line)?????
>73
>Riki K7NJ - 4X4NJ
30 + dB is easily obtainable at the deepest part of the null with a single
filter. But the Q is fairly high.
40 + dB is easily obtainable with the typical dual-stub filter. With proper
stagger tuning it is possible to maintain 40 dB over a broader range.
I always use twin stubs--1/4 wave apart on the harmonic to get a solid
30 + dB over most of the band/mode.
I can't provide specific patterns--my notes are all at the Colorado QTH.
--John
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