Dick wrote:
Danny Richardson wrote:

I would be far more concerned as to what its common mode impedance is.
From what you describe it sounds like a voltage balun and those
generally have a poor common (blocking) mode impedance.

Danny, K6MHE


I would guess that you are right Danny and this is a voltage balun. I dug
it out as I have recently moved to a flat in the centre of town 100 yards
from a large telephone exchange and surrounded by noise sources. My old
trusty vertical is giving me so much noise here that I want to put up a
balanced antenna in the hope that this will reduce the interference. To
minimise this noise I need a well balanced system. I already have coax up
to the roof and balanced line would be difficult to route so am planning
to
fit a balun either at the dipole centre or a few feet below with a short
balanced feed. I dug this balun out as it looked like it would give good
balance. I have another (current) balun which has a simpler bifilar
winding. I'm not sure which will be best for my application.
Incidentally
I only run QRP so efficiency is a major factor. I also considered a
folded
dipole using 600 ohm line as that would be less prone to static noise but
would then have to look at a 4:1 design.

73 de Dick G4BBH


Hi Dick,

Have you considered a simple "Ugly Balun" (http://tinyurl.com/uvnt3)? It is
nothing more than the end of your feedline coiled up, at the antenna
feedpoint. Another better approach is a stack of ferrite cores at the
feedpoint. These are commecially available, though you can easily make your
own. I found some good reading he http://tinyurl.com/uzvkh.

A folded dipole will look like 300 ohms. A 4:1 balun will present 75 ohms to
the feedline; you'd need a 6:1 ratio in order to see 50 ohms.
That aside, a multiwire dipole (such as a folded dipole) will exhibit
greater bandwidth than a single-wire dipole. My experience says that (at
80m) you'll see ~ 100 KHz for each set of wires, whether they're in the form
of fan dipole, cage dipole, or folded dipole. I prefer a cage dipole over
the other two:
1 - same number of supports as with a single-wire dipole or folded-dipole
2 - matches directly into low-Z coaxial cable
I use one (in inverted-vee form during Field Day
(http://tinyurl.com/ybbsba)... approximately 400 KHz bandwidth, and uses
easy-to-make spreaders.

Vy 73 ob,
Bryan WA7PRC