1:1 balun for Inverted v

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Joseph Miglino:
Dave KD8GEH,
I was thinking PVC, but the plastic coffee can idea saves me a trip to Home Depot, (but I got to tell you I could spend 6 hours wandering around that place.)
I would love to encapsulate the entire thing in shrink tubing, but I doubt they make it 8+ diameter.

Burning 20~22 ft of coax for a choke does not make happy, but it is what it is. Would that length still applied when using RG-58?

Thx,
Joe

Cecil A. Moore:
6 turns of coax doesn't give much choking impedance on 40m. The following article sheds some light on the ugly balun problem.

http://www.k1ttt.net/technote/airbalun.html

For 40m, it says:

            6 Turns
           4-1/4 in
          sngl layer
          ----------
Frequency  Mag Phase
7.00E+06   190  89.4

190 ohms is not nearly enough for an effective choke. 1000 ohms is a lot better. Some antennas (not a resonant inv-V) need a 10k ohm choking impedance.
--
73, Cecil, w5dxp.com

Robert Morris:
One can increase the choking effectiveness by adding a second choke of this design. One at the antenna and one at the equpment. Just a heads up. 73

Dave Z:
Cecil & Owen both have good points and are much more knowledgeable than I.  

I use my chokes generally on multiband di-poles, loops and inverted L's.  Check out the site Cecil mentioned, really good data there. They imply that straight 40 meters, 12 turns of 213 works well. That’s a pretty big choke, and as mentioned, without proper equipment, there is a bit of trial and error.  I have used the same method with 58 no known issues. I run up to about 600 watts no RF in the shack. With lower power, its less of an issue in my experience.

73,
Dave KD8GEH

Joseph Miglino:
Cecil W5DXP,

Thanks, I found the article to be just what I what I needed and even printed it out (I don't care what anyone says, reading off a computer monitor does not compare at all with reading from a piece of paper physically in one's hands.) Up to now the info I have found on air wound chokes has been based anecdotal evidence, not to  say it's incorrect, the article's author provided empirical results that I could more confidently hang my hat on.

I wish I could find a Java Applet calculator for air wound chokes.

Thanks again,
Joe

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