"Richard Harrison" wrote in message
...
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..
Hey, Richard -
Take a look at Roy's second paragraph:
"If you're dealing with an air-dielectric folded dipole, the transmission
line stub is nearly a quarter wavelength long. So at resonance, its
impedance is high and it doesn't have much effect on the feedpoint
impedance. As you lower the frequency or shorten the antenna, the
resistance of the antenna (as opposed to the transmission line) drops
fairly slowly, and the reactance becomes negative relatively quickly.
This is in parallel with the transmission line, whose reactance becomes
more positive as the line gets electrically shorter. If you look at the
net result of this parallel combination, you get a feedpoint impedance
that has a rising resistance as frequency drops or the antenna shortens,
and a reactance that gets more negative."
What Roy is saying is also what I'm seeing with EZNEC. You are saying the
opposite reactance occurs with a folded monopole.
John
|