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
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