[RFI] Yet another balun question

[N1BUG]

Hi Jim,

Thanks for responding.

Comments below.

> 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.

Correction noted. In theory I should know better.

> Orientation of one choke to another is not critical. For all practical
> purposes, the field is confined to the ferrite core .

OK. I was thinking capacitance between turns of adjacent chokes 
might come into play if they were quite close, say an inch or two.

> 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.

Good. For some applications, depending on number of turns and 
mounting, I like the visual symmetry of that approach. I know that 
is being ridiculous. I am often ridiculous.

> You didn't say how much power you want to run through it or what the
> antenna is.

100 watts on 30 meters, 1500 watts on 40 meters. The antenna is a 
rotatable two band dipole. See below.

> 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.

I have been using chokes of 16 turns RG-303 on 160 meters, 16 turns 
#14 THHN on 80 meters, 14 turns on 40, 13 turns on 30, and 12 turns 
on 20-10m, all on #31 material. I have yet to experience a failure 
at 1500 watts on my wire antennas. Perhaps I have been lucky. I 
considered it marginal when I built them.

I have no evidence to back this up, but I am concerned the TH-11DX 
antenna below the new 40/30 meter dipole may introduce significant 
imbalance. The 40/30m dipole will be parallel to TH-11DX boom. I 
want to design for more choking impedance to be on the safe side. I 
plan to use #43 material for these chokes.

My bifilar chokes are a little different than what you describe in 
your tutorial. I made sure the wire was very straight, then bundled 
into pairs with a continuous wrap of tightly wound teflon plumber's 
tape.

> 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.

Understood. I have yet to see any objectionable affect on SWR using 
#14 THHN.

73,
Paul N1BUG