Just today, I happened to revisit a voltage balun I wound years ago for my
FD 80/40m inverted vees. It started out as an Amidon AB240 kit (Amidon
#FT-240-61 or Fair-Rite #5961003801 ferrite core). On the network analyzer,
it looked kinda cruddy... the ratio wasn't quite 1:1, and there was a bit
too much reactance in the measurement. I rewound it as a
super-inductor/choke balun with RG-58 like this:
http://www.iol.ie/~bravo/low_band_antennae.htm

Now, it IS 1:1 (by nature of the RG-58), and there is hardly any rectance
(less than an ohm up to about 20MHz). Common-mode reactance is about 200
ohms at 1.8 MHz, and 400 ohms at 3.5 MHz. I didn't bother checking above
80m.

Vy 73,
Bryan WA7PRC
PS: The correct link to Roy's info is a PDF file:
http://www.eznec.com/Amateur/Articles/Baluns.pdf

Roy Lewallen wrote:
Without a balun, your feedline could become part of the antenna. If
noise is being radiated by such things as house wiring, the feedline
part of the antenna is likely to pick up more noise because it goes near
and into the house. A current balun prevents the feedline from becoming
part of the antenna and so it can reduce the noise.

A lot of local noise is predominantly vertically polarized. So if you
have a horizontal antenna without a balun, the feedline, which often is
vertical, can pick up a lot more noise than the antenna. Again, a balun
prevents feedline pickup and can make things quieter.

If you're feeding the antenna with coaxial cable, put the balun at the
feedpoint. If feeding with twinlead, put it where the feedline connects
to the tuner or receiver.

To learn more about baluns, see
http://eznec.com/Amateur/Articles/Baluns.htm.

Roy Lewallen, W7EL

Bill Ogden wrote:
A discussion on the towers reflector mentioned, in passing, that a
current
balun helped lower received noise. The discussion was about something
else
and this aspect was not explored.

Is this common? I had never heard of it before, but I many holes in my
understanding of antennas. Under what circumstances would this apply?
Where
would the balun (toroids) be placed? Feed point or at bottom of tower?
(My
particular interest is for use with a half sloper and for 160/80/40
meters.)

Bill
W2WO