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Re: [CQ-Contest] Bandpass filtering

To: <cq-contest@contesting.com>
Subject: Re: [CQ-Contest] Bandpass filtering
From: "S56A" <s56a@bit.si>
Date: Fri, 31 Dec 2010 00:31:11 -0000
List-post: <cq-contest@contesting.com">mailto:cq-contest@contesting.com>
N4ZR wrote: From what W3LPL has told me, I am pretty confident that I can 
simply parallel the output of the 6 filters, but can I also parallel the 
inputs?

I very much doubt that W3LPL told you that!  His BPF are triple tuned 
circuits with top capacitor coupling.  They exhibit low impedance on the 
frequencies above bandpass.  10 m filter is coupled to 50 Ohms with 33 pF 
while 160 m has 719 pF.   That gives 475 (square) power ratio or -27 dB 
loss.

Only serial tuned circuits can be paralleled at 50 Ohms and even that 
becomes difficult beyond triplexer.  Check http://www.nuhertz.tv/

You don't need any BPF for QS1R, just band STOP filters to prevent input 
frying from nearby TX.  ICE filters might be easily converted to band-stop 
with change of both inputs to serial notch and adding just one more small 
coil for parallel resonance (de)coupling.

HNY & 73 de Mario, M/S56A from London


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