http://elecraft.85.s1.nabble.com/ladderline-and-balun-question-tp7179004p7179217.html
Don:The gentlemen with the 1 wave loop on 160 could extend the 450 ohm feeder out where it presents a current loop That would place him at a current loop on 80, as well or, just continue with the 450 ohm line (a multiple of half waves) into the shack and couple up there.He could place the balun at at any current loop, or better yet, a link coupled balanced matching network in the shack.Bst RgdsBill-w7kxb
> Date: Wed, 11 Jan 2012 17:02:51 -0500
> From:
[hidden email]
> To:
[hidden email]
> CC:
[hidden email]
> Subject: Re: [Elecraft] ladderline and balun question
>
> Don,
>
> According to L B Cebik's modeling, a 2 wavelength horizontal loop will
> have a feedpoint impedance of 180 - j125 ohms, and a 4 wavelength loop
> (the same loop used on 80 meters will have a feedpoint impedance of 235
> - j135.
> Both are good candidates for the use of a 4:1 balun - but that only
> applies if you mount the balun right at the antenna feedpoint. The fact
> that you have 60 feet of 450 ohm feedline changes the situation
> drastically - that is about 1/8 wavelength on 160 and close to 1/4
> wavelength on 80 - so the feedoint impedance at the end of that 60 feet
> of feedline is quite a bit lower - that is most likely why your 1:1
> balun worked so well. You can work with L B Cebik's antenna feedpoint
> impedances and the TLW application available from the ARRL to find the
> feedpoint impedance at the end of the 60 foot feedline, but I think you
> will find it closer to 50 ohms than to 200 ohms.
>
> The other question is what type of balun is your 4:1 balun - if it is a
> voltage type, it has no chance of stopping common mode current.
>
> My guess for why your current choke did not work is either that you did
> not place it at the right point on the coax, or it was at a point where
> the RF voltage was high, and in light of a high RF voltage (think
> impedance equal to 2000 to 4000 ohms, a choke of 5000 ohms impedance
> does not have much of a chance to stop any current.
>
> So bottom line - go back to what you had before, or put the 4:1 balun at
> the antenna feedpoint where it should work if your antenna is anything
> like L B Cebik's simulations.
>
> 73,
> Don W3FPR
>