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Wimpie[_2_] · April 1st 14, 10:20 PM posted to rec.radio.amateur.antenna

El 01-04-14 21:33, escribió:
wrote:
Channel wrote:

Radials on a elevated antenna only works if the radials are placed at or
near the bottom of the antenna and are arranged at a 45* angle.

Any other angle and you might as well not have any radials at all!

Utter nonsense.

The radials do have to be at or near the bottom but the angle of the radials
mostly determines the antenna impedance.

With the radials at 90 degrees the impedance will be around 40 Ohms and
at 45 degees very close to 50 Ohms.

One can download the demo version of EZNEC and observe the effect of
radial angle for themselves.

On a 10 -12 meter antenna, these radials would need to be at least 1/4
of a wavelength long - 9 feet and preferably 18 feet long to do any
good!

The ideal radial length for ANY ground plane antenna is slightly longer
than 1/4 wavelength, no matter for what frequencey.

If you coil them up they do not work as intended, but they might help a
little.

If you coil them up, you are inductively loading them, shortening the
physical length just like a loaded vertical.

If you make them electrically around 1/4 wavelength, loaded radials will work
just fine.

Ground plane antennas have been made with 4 hamsticks; 1 for the vertical
element and 3 for the radials and they work.

They major drawback to such is the limited bandwidth of loaded antennas.

snip remaining babbling nonsense

Slight correction:

At 90 degrees the impedance will be close to 20 Ohms and at 30 degrees
close to 40 Ohms if not very close to the ground.

Jim, nice detail! Many reference say 35 Ohms (as they assume an
infinite ground plane), but it is really as low as you stated.

For JOTA oparation we used a 6 elevated radials arrangement at 40 m
band and I had to extend the radiator to get 50 Ohms. Just adding a
tuning capacitor "removed" the inductive component. Now we have the
means to erect a half wave giving sligtly lower main beam elevation,
and we use 3 radials now.

It would help if you were to specify what band or bands you are interested
in and how hight this balcony is off the ground.

--
Wim
PA3DJS
Please remove abc first in case of PM

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