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@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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