Posted by
Don Wilhelm-3 on
Apr 29, 2006; 10:51pm
URL: http://elecraft.85.s1.nabble.com/Elecraft-balun-tp389237p389239.html
Fred,
If you have a phasing line connected to the antenna, and attach the balun at
the junction of your coax and the phasing line, all should be well - you can
then use any length of coax from the balun to the shack.
BUT - you said your phasing line was coax (which is unbalanced), so I figure
you would not want to introduce a balun at a junction of coax to coax
(however a unun may be appropriate). If your coax phasing line is attached
to a balanced antenna, then I would think you would place the balun right at
the antenna center feedpoint. OTOH, if this is one of those special
offcenter-fed antennas, you may not want to use a balun at all - at least
one of the Elecraft BL1 configuration. If you want to keep RF off the outer
shield of the coax, then a ferrite bead balun or a coil of coax is the best
solution - place thone of those either at the shack entry point or at a half
wavelength interval from the antenna.
To answer your direct question, one would have to know the relative
impedances of your entire antenna system as well as the lengths of each part
of it - even if one knows the transmission line characteristics of the
Elecraft balun for a 50 ohm load that is no assurance that the behavior will
be similar at other impedance levels. We would have to calculate the
feedpoint impedance of the line at the point where the balun is inserted.
73,
Don W3FPR
> -----Original Message-----
>
> I want to use my Elecraft BL-1 1:1 balun on field day.
>
> The balun would serve as center insulator, but the coax line
> plugged into it is a phasing line.
>
> Here is my question: Will the windings on the balun, introduced
> between the antenna and the phasing line, effectively increase
> the length of the phasing line?
>
> I think it will, and I am wondering by how much to shorten my
> phasing line to account for it. I think the windings are six to
> seven inches in length and would imagine the velocity factor to be high.
>
> 73
>
> Fred - kt5x
> K2 # 700
>
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