(Richard Harrison) wrote ...
Around the 1/4-wave length, the folded monopole`s resistance is steadily
rising with frequency. High radiation resistance as compared with loss
is good. This happens with the open-circuit 1/4-wave vertical too.

Around the 1/4-wave length, the folded monopole undergoes an abrupt
change from inductive reactance when it is too short for resonance to
capacitive reactance when it is too long for resonance. The open-circuit
whip undergoes a similar change but it has a capacitive reactance when
it is too short for resonance and an inductive reactance when it is too
long for resonance..


Not to be picky and unncessarily perpetuate this discussion, but it's
already been correctly stated in this thread that a folded monopole or
dipole exhibits the same impedance characteristics around resonance as
a conventional antenna. That is, when it's too short for resonance,
reactance is capacitive, and is inductive if too long. And resistance
is 4 times the resistance of a conventional antenna, and actually
*increases* on either side of resonance, according to models.

The above statements are only true in the region of operation around
1/4 wavelength (folded monopole). As frequency or length is decreased
more significantly, past the anti-resonant point (something that
doesn't happen with conventional 1/4-wavelength monopoles), its
characteristics take on a completely different twist, where reactance
suddenly becomes (and stays) inductive and decreasing, and resistance
decreases rapidly.

A folded monopole (or folded dipole) is, in some respects, like two
different antennas, with two different sets of characteristics,
depending on whether you are operating above or below anti-resonance.
One of the problems in discussing folded monopoles/dipoles is because
of just this reason -- you simply can't make general statements about
how it works unless you also provide some of the parametric
assumptions.

Al WA4GKQ