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Re: [TowerTalk] Is anyone using the 3 feedline approach ontheC31XRfor SO

To: "Dan Zimmerman N3OX" <>, <>
Subject: Re: [TowerTalk] Is anyone using the 3 feedline approach ontheC31XRfor SO2R?
From: "Tom Rauch" <>
Reply-to: Tom Rauch <>
Date: Tue, 5 Jun 2007 11:54:14 -0400
List-post: <>
> If you modeled this, did you include loads in the centers 
> of the
> elements that go to other radios that model the effect of 
> the
> feedlines terminated in the stubs and bandpass filters for 
> the other
> radios?

Modeling a system like this is very complicated since the 
input impedance of the radio on receive and the output 
impedance of the PA stage on transmit when looking back into 
the PA sets the load on the transmission line for the 
non-excited yagi section.

Then, since that is almost certainly a large mismatch, you 
have transmission line effects to add in.

You'd either have to know all the information exactly, which 
no one does, or assume a worse case condition and play with 
loads at the antenna until coupling is maximized.

A better solution would be a very high Q shunt system at the 
feedpoint of some known distance from the feedpoint that 
establishes a near zero impedance at the undesired 
frequencies. That would make it easy to model interaction.

The bottom line is to be safe we need isolation within 
several dB of the value a common feedline would require. It 
certainly does simplify splitting and combining, but not 
filtering to any significant extent. Expect big smoke 
without the filtering.

73 Tom


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