Topband: Elevated Radials
richard at karlquist.com
Tue Mar 5 20:42:41 EST 2013
One of the problems with discussing this topic is that
nearly all studies of radials deal with 1/4 wave verticals.
Most ham stations including mine don't have the luxury of
a height of 130 feet.
There are many cases where some "novel" grounding scheme
is touted as "just as good as 120 radials" and indeed it
may be for the 1/4 wave height case.
What is scarce is advice for the owner of a short vertical
as to what to do about grounding. What grounding scheme
would it take to make the proverbial 43 foot vertical play
as good as a 130 foot vertical? Whatever that scheme is,
we know that it will have very narrow bandwidth. This is
a good litmus test to separate short vertical installations
worthy of additional testing from low efficiency ones. Of course, narrow
bandwidth is merely necessary, but not sufficient, to
prove high efficiency. The advantage of the bandwidth
criterion is that it is easily and unambiguously measured,
as opposed to field strength. The bandwidth should ideally
be determined by measuring the antenna drive impedance
directly, rather than looking at it through a matching
network. A matching network will to a greater or lesser
extent decrease the bandwidth of the antenna. Alternately,
the matching network can be modeled to remove its effect
I think it is less likely that you can be fooled by a bandwidth
measurement than you can with base impedance measurements.
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