[Cu-wireless] Summary of antenna test results

[Paul Riismandel]

At 03:58 PM 11/12/2001 -0600, Dave wrote:
>I had a hunch that we'd get better reception with all antennas at a height
>off the ground.  I only tried the Pringles. At 1.3km, we got 25dB when
>I stood on top of the van with the Pringles can antenna, 20dB with the
>same antenna when I stood on the ground beside the van. I suspect that
>the ground plane of the earth affects reception (there appears to be a
>lot of discussion of some such phenomenon in the ARRL Antenna Handbook),
>but there's no telling. It was not a very scientific test, climbing on
>the roof of the van.

Yes, I'd suspect that the Pringles can provides a ground plane of some sort 
that is lacking in the NCSA antenna, and unnecessary with the parabolic 
(which is well tuned and focused to the frequency range in question).  I 
can only guess at what this specific parabolic antenna looks like, but I'd 
guess you could probably make similar antennas with sheet metal, metal 
screen or some other conductor, since it appears to me that the foil in the 
pringles can acts as both a collector/reflector, like a parabolic dish, and 
as a ground plane radial, like a ground plane antenna.  My antenna 
knowledge at this wavelength is minimal, but I'm pretty sure that the 
ground plane effect is not terrifically useful for line-of-sight 
applications.  At least in the VHF band it's mostly useful for 
omni-directional broadcasting (many FM antenna designs utilize ground 
planes). Ground planes become much more important at lower frequencies, 
especially around the AM broadcast band.

--Paul