A coil loaded elevated shorter radial system, intended as a counterpoise
rather than a ground plane, can still offer a reasonable antenna efficiency.
Unavoidable gap of an efficient antenna of this type is a very narrow
bandwidth when the counterpoise is short and the loading is big.
The required conditions to save the efficiency are low losses along antenna
elements (loading device's Q must increase with bigger loadings, so it's
better not to exceed in shortening the counterpoise) and a minimized ground
losses.
In the case where coils are used (better one for each radial) to resonate
a counterpoise, they must be size proportioned to the used power, must have
an high Q and beeing preferably placed far from the antenna highest current
points.
It's useful to remember that a properly elevated counterpoise made of only 2
opposite radials is already enough to generate the classic omnidirectional
pattern of a vertical antenna and with limited losses compared to a classic
ground plane antenna.
73,
Mauri I4JMY
-----Messaggio originale-----
Da: Tom Rauch <w8ji@contesting.com>
A: towertalk@contesting.com <towertalk@contesting.com>; R. Sigismonti
<n3rs@cynet.net>
Data: domenica 4 luglio 1999 18.21
Oggetto: Re: [TowerTalk] PVC & Losses
> Wonder if anyone could comment on the use of 4" OD PVC Tubing as a form
> for a loading coil that will be used in an above ground shortened radial
> system on each element of a 4-SQUARE? Should I hunt around for
> Polyethylene or is the PVC OK for this type application.
Hi Sig,
Since a coil loaded elevated radial system is pretty inefficient
anyway, I don't think the loss of Q caused by using PVC would
hurt much anyway.
If the system had reasonably high efficiency, then the PVC would
be a problem.
I would worry about moisture detuning the coils. Put them in some
kind of enclosure that keeps water away from the coil.
73, Tom W8JI
w8ji@contesting.com
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