[RFI] Yet another balun question

[Kim Elmore]

I've a question about number of turns. Using enameled wire on a 2.40" core, I've made these with -20 bifilar turns. I know there's a point of diminishing returns due to distributed capacitance. Am I near that with 20 turns or well past it?

Kim N5OP

"People that make music together cannot be enemies, at least as long as the music lasts." -- Paul Hindemith

> On Jun 28, 2016, at 17:29, Jim Brown <jim at audiosystemsgroup.com> wrote:
> 
> Hi Paul,
> 
> First, let's call a spade a spade -- it's not a "balun" or even a "current  balun," it's a common mode choke.  What we CALL it helps us understand what it is and what it does.
> 
> See more comments below.
> 
>> On Tue,6/28/2016 1:47 PM, N1BUG wrote:
>> I am sorry to ask this, but the probably obvious answer isn't obvious to me.
>> 
>> Assume I want to make a current balun consisting of two (or more) chokes in series. Assume each choke will consist of a single 2.4" toroid core wound with RG-303 coax (RG-58). Question: What should I be looking at for physical orientation of one choke to another, and distance between them? I am assuming that if nothing else, capacitance between turns on one choke and turns on another choke would be a consideration. Any guidance?
> 
> Orientation of one choke to another is not critical. For all practical purposes, the field is confined to the ferrite core .
> 
>> Second question: I think I read somewhere that there is little difference in performance between all turns on a single such choke wound "sequentially" around the core vs, winding half, then passing the coax through and 180 degrees across the core, then winding the remaining turns such that the coax leading into the choke and the coax leading out can be 180 degrees opposed to each other.
> 
> As far as I know, this method was proposed by W1JR for a choke he wound on a #61 core. I've wound such a choke and measured it, and I've never been able to see a difference between it and a sequential choke. Joe is a fine engineer, but I've shown (in my tutorial) why #61 is a terrible material for a common mode choke for the HF bands.
> 
> You didn't say how much power you want to run through it or what the antenna is.  For 80M to about 15M, one of the bifilar chokes I've described wound with 12 turns of a pair of #12 enameled wire or #12 THHN should provide about 5K ohms of choking Z. If the antenna is reasonably well balanced and resonant, it should be good for at least 600W. For higher power and/or significant imbalance, two such chokes in series would be a good solution. With enameled wire, Zo is about 50 ohms. With THHN, it's closer to 80-90 ohms. Jerry Sevick described chokes like this in one of the later versions of his classic work, and noted these values for Zo. I've made both types and measured them, and got the same result. This is for closely spaced pairs.
> 
> 73, Jim K9YC
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