[TowerTalk] W1JR Balun [was: Balun filler]

[Chuck Counselman]

At 10:38 AM -0400 7/18/03, Joe Reisert W1JR wrote:
>The "W1JR Balun" uses a 2.4" OD ferrite core. The winding consists 
>of 12 turns of RG141 or RG303 (the later recommended) teflon coax in 
>a "contra-wound" fashion....

An appendix of the RSGB book on EMC teaches this style of winding.


>The core used is the standard 2.4" OD called the T240 by Amidon and 
>others. The material used is Fair-Rite type 61 (Indiana General Q-1) 
>which has a initial permeability of 125.

Excellent choice.  I've used Fair-Rite type 61 in my baluns and 
un-uns, too.  It has very low loss so it won't get hot at high power 
as type 43 or (worse) type 77 will.


>If you use 12 turns, the impedance will be greater than 500 Ohms at 80 meters

I can confirm this.

>...and typically much greater than 1,000 Ohms from 7-30 MHz with no 
>resonances.

I'm not disputing your statement, but I have not confirmed that a 
12-turn winding has no resonance below 30 MHz.  _A_priori_, I'd 
expect it to.  I'll measure one and report back.


>I hope this helps answer your questions.

Yes; thank you.

73 -Chuck, W1HIS