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SWR Indicator for balanced line

Questions and solutions about your antenna and feedline projects.
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VE3PCP
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SWR Indicator for balanced line

Post by VE3PCP » Sat Sep 30, 2017 8:11 am

Hi:
Many years ago I made one of these and it worked very well as a basic indicator of SWR on 300 ohm twin lead which I have used for many antennas over the years.
I just taped it to my feed line right after the tuner so I could see it from my seated position while operating.
Not sure how many of you use balanced line but here is a link to the article about how it works and how to build one.
Enjoy!
Rob
VE3PCP
http://www.rfcafe.com/references/qst/tw ... r-1947.htm
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VE3PCP
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Re: SWR Indicator for balanced line

Post by VE3PCP » Sun Oct 01, 2017 7:38 am

I rebuilt my unit yesterday and did up a short video to explain it and show it in operation.
Enjoy!

[BBvideo=560,315]https://youtu.be/TBWElwXIBXU[/BBvideo]
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va3ts
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Re: SWR Indicator for balanced line

Post by va3ts » Fri Oct 20, 2017 10:31 pm

Some history and theory on open wire feeder and swr

[BBvideo=560,315]https://youtu.be/w1eE13UXAKs[/BBvideo]

open line - spacing usually < 1% of the wavelength

When the line length is an even multiple of wavelength/2 , the input resistance is equal to the load resistance, regarless of line Zo.

The characteristic impedance of air insulated parallel conductor line
Zo=276 log 2s/d where s = center to center distance d = outer diameter of conductor
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