In article ,
John Smith wrote:

When using balanced antennas such as loops, dipoles, etc. a voltage
balun can be used, however, great detail should be paid to the
symmetry of the antenna and even one leg of a dipole being nearer a
metal building, trees, etc. can effect that symmetry.

You are better off with a current BALUN type. They have a wider, flatter
response and are usually more efficient.

When using unbalanced antennas end fed, long wire, monopole, etc. a
unun is better used and will even eliminate most common mode
currents.

Well, I think you mean noise currents. The signals the single element
antenna picks up are also common mode.

Here the voltage type UNUN has the advantage of DC isolation between the
receiver and antenna where it can direct static voltage potential to
ground. With a receiver plugged into the mains AC supply noise from that
system can conduct on the outside of the coax or the coax itself can
pick it up if it goes by a noise source. Once it reached the antenna
connection it can couple to the antenna. The two circuits of the voltage
transformer can be independently grounded so that the antenna RF ground
is not the same as the coax ground where the mains noise is going.

Single wire element antennas (random wire, long wire) are a Marconi type
where the other half of the antenna is ground. If you only have one
ground then RF ground for the antenna is also a noise current ground
where they can mix.

The mode these antennas pick up signals is common mode so the antenna
needs to be in a RF quiet environment or you are wasting your time. This
usually means you need to be living in a semi-rural to rural area or you
cannot get the antenna far enough away from your house or your
neighbors. I live in an urban environment and a Marconi antenna picks up
way too much noise to work well.

--
Telamon
Ventura, California