Hi,

Thanks for reply.

Tests were done indoors.
Various locations; similar results.

Best regards,
Bob

------------------
"Wimpie" wrote in message
...
On 14 ene, 14:47, "Robert11" wrote:
Hello,

Not an antenna expert, so thought I'd post my questions here, for all you
theorists.
Would appreciate any thoughts on the following, as it really confuses me.

Have a new handheld scanner; GRE 500 model.
Has a rubber duckie for its antenna, which is pretty typical for these
kind
of scanners, of course.

Tried listening to an airport control tower (118.5 MHz AM), about 5
miles
from the house.

Here's what I found playing around.

When the unit is held normally, that is with the antenna vertical, the
airport comms from the tower were really poor.
Lots of static and noise.

But, much better when held horizontally.
a. Any idea why ?

I would have thought that their antennas would be polarized vertically
to communicate with planes.

b. any idea how their tower antennas are likely polarized (if at all) ?

c. and this one really confuses me.

The best reception, by far, is if I point the antenna vertically, but
DOWNWARD ! Big difference from vertically up.

Wouldn't vertically up, and vertically down be identical and
symmetrically
the same re polarization, reception, etc. ?

Thanks,
Bob

Hello Rob,

Did you do the tests indoor, or very close to objects?

As far as I know, VHF AIR comms are vertically polarized (ground
station).

Due to reflection and refraction, polarization may change and the
field will no longer be uniform. So the strength and polarization
varies with position of the antenna. This is also valid for various
sources of interference.

Your rubber duckie will be part of the antenna; your hand, arm and
body will be the rest of it. Your hand serves as ground / opposite
pole for the antenna. Probably you will find more spots where you have
better reception (or even no reception).

I live about 16nm SE of EHAM (Schiphol Amsterdam, Netherlands), flat
terrain profile, very thick full wave dipole, 30 ft height above
average terrain. Signals from ground control are strong; signals from
airplanes at airport are reasonable. I use a 3 pole preselector to
attenuate broadcast signals. When you are going to use a larger
antenna, you may get intermodulation problems also.

Best regards,

Wim
PA3DJS
www.tetech.nl