On Mon, 2008-05-05 at 06:02 -0700, Jim WA9YSD wrote:
> Voltage balun or Current balun. With out any fancy clamp on RF current
> meters and the sort, what are some simple things can the average ham can do
> to determine if a Current balun or a Voltage balun is needed when working on
> different types of wire antennas fed with either coax or open line?
>
> Proper way of doing things is to use a voltage balun at the feed point of the
> antenna followed by a current balun, right? Now there is a beast called a
> Hybrid balun that take the place of the combo. Who sells this Hybrid? Is
> this the best way to go? Why?
>
> Keep The Faith, Jim K9TF/WA9YSD
>
>
You use a voltage balun when you want the balun to force the balance,
even if the antenna isn't quite balanced. Works many times and works
well if the antenna is balanced.
You use a current balun when you want to balun to let the antenna
balance control the currents and you want to keep unbalanced currents
from the outside of the coax. Also works.
Neither balun will work well at keeping RF off the outside of the coax
if the coax leaves the antenna not at right angles to the antenna.
Keeping RF off the outside of the coax is handy in cutting TVI and
received noises from stuff in the house. Its handy when wishing to
confine the radiation of the antenna to one polarization. Its handy at
VHF and up with balanced fed yagis that outperform gamma match fed
elements. Sometimes not having a balun at the antenna and having RF on
the outside of the coax allows making contacts that wouldn't otherwise
be made because the radiation from the coax has a radiation pattern that
includes the desired station that the main antenna doesn't. So the balun
isn't always the best answer. E.g. lack of balun makes the feed line act
as an antenna saving having to have two antennas with different
polarization for each band.
73, Jerry, K0CQ
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