Amos Keag wrote:
. . .
3) A balanced feedline is used for a balanced antenna, e.g. dipole etc.,
to minimize RF coupling to the transmission line. The balanced line
needs to run away from the antenna for a minimum of 1/4 wavelength at
right angles to be effective. A dipole fed with coax cable needs a balun
to produce a balanced signal to the antenna. The coax should also run
away from the antenna at right angles for 1/4 wavelength to be effective
in minimizin current on the coax. If you need to run from the antenna at
less than 1/4 wavelength then a series of chokes or ferrites should be
used to keep RF out of the house. These chokes/ferrites should be
mounted at least 1/4 wavelength from the antenna.

A symmetrical feedline is no guarantee of balance. Balance is achieved
only when the two conductors carry equal and opposite currents, and that
can be achieved with either coax or symmetrical feedline. Likewise,
imbalance can occur with either type of feedline. You can learn more
about the issue at http://eznec.com/Amateur/Articles/Baluns.pdf. That
article doesn't mention imbalance caused by coupling to the antenna,
which can occur if a dipole isn't symmetrical or if either type of
feedline is asymmetrically placed relative to the antenna.

Roy Lewallen, W7EL