Dan Jacobson wrote:
Yes! Say, can one just cut the reflector 5% longer than the antenna?
The antenna is some complex double 5/8 wavelength job.
If the reflector is shorter than the antenna, it becomes a director?

Nope, the reflector needs to be 5% longer than 1/2WL.
A 5/8WL antenna is NOT resonant. Passive elements must
be close to and referenced to resonance.

I had a vertical loop resonant on 17m. I installed a
reflector 1.05 x (1/2WL of 20m). It became a beam on 20m.
--
73, Cecil http://www.qsl.net/w5dxp


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On Wed, 16 Feb 2005 04:29:38 +0800, Dan Jacobson
wrote:

D It might well be worth your while to experiment with a simple
D somewhat-directional antenna. A single reflector, located perhaps
D .1 to .2 wavelengths on the mountainside side (sorry :-) of your
D current vertical, cut to perhaps 5% longer than a half-wavelength,
D could be used to shape your antenna's pattern into something
D vaguely cardioid.

Yes! Say, can one just cut the reflector 5% longer than the antenna?
The antenna is some complex double 5/8 wavelength job.
If the reflector is shorter than the antenna, it becomes a director?
What if the reflector is just a pole jabbed into the ground, thus
grounded and longer downwards than the 5%? What if the pole is "very
much longer than the antenna in both directions"?
How about the thickness of the reflector? Only as thick as the antenna
itself (but wait, the antenna has two thicknesses, top thin, bottom
thick), or just grab any iron pipe (wait, metal type and shape
important?)


I am going to take a stab at this.
I would think that the 5% greater than the 1/2 wave will be a better
reflector than the 5% greater than 5/8 wave. I am thinking that the
wavelength of the signal is what we are dealing with more than the
size of the transmission element.

I did a very non-scientific experiments with rubber duck antennas and
beam elements many years ago. One of the tricks I used was to put a
rubber duck between the reflector and driven elements of a small beam.
The signal improved radically. I also tried it with three rubber duck
antennas. The reflector duck had an extension to make it a little
longer. The change in the signal strength was, as expected, a little
improved, but not greatly.

I also placed a 5/8 wave j-pole between the reflector and director.
It produced a better signal than the rubber duck did, but not as much
as I had expected. I didn't go any farther with the experiment. I
didn't keep a log or use calibrated equipment or anything. Like I
said, I was just playing around with it a few minutes.


--
73 for now
Buck
N4PGW