[Antennas] dipole question

2002年8月18日 15:04:40 -0500

"George, W5YR" wrote:
> > OK, let's go to a 140' folded dipole made with 600 ohm ladderline for the
> > horizontal element, and fed with 450 ohm ladderline. Will this one load 160
> > much easier than the simple dipole?
>> First, a folded dipole does not behave any differently from a conventional
> wire dipole. Adding the second parallel element and connecting them
> together at the ends just raises the driving-point impedance by a factor of
> four (number of conductors^2). So, you don't want to use 600 ohm line for
> the flattop since that would give you a 2400 ohm input Z with you trying to
> feed it with 450 ohm ladderline.

I have to disagree here George (your math is somewhat flawed above)
A dipole is always 75ohms for argmument sake; yes it will vary +/-
due to height above ground, etc.....BUT regardless of wire size,
the average single wire dipole is 75ohms....a FOLDED two wire dipole
is always then 300ohms at feed point....regardless of the Z of the wire,
spacing, etc used in the folded dipole....I cannot see how using 600ohm
Z line for the dipole element makes it 2400ohms at the feedpoint...
The Ladderline's Z used for the DIPOLE element is a moot point...
The same rules apply to it as a std dipole or folded dipole..
Folded dipole (conventional) is usually 300ohm Z...+/- 10-20%...
Chris
WB5ITT