Bill,
Beverage antennas are very lossy and tightly coupled into the nearby
Earth, as a result there is virtually no mutual impedance among even very
close spaced Beverages. It's very simple to experimentally confirm this
by pumping RF into one Beverage and measure the loss into an adjacent
Beverage (a spectrum analyzer with tracking generator is an easy way to
measure this). Parallel Beverages spaced from each other by the same
distance as their height above ground have about 30 dB of isolation
(somewhat dependant on ground properties).
One way in which the efficiency of Beverage antennas can be improved is
by use of multiple close spaced Beverages. This distributes the currents
flowing in the ground and significantly improves their efficiency. This
is a common approach for Beverage receiving arrays operated above 7 MHz.
A common configuration is three Beverages, 4 feet high and 4 feet from
each other, and their efficiency is about 3 dB better than a single
Beverage (again dependant on ground properties). The commonly used feed
mechanism is to bring all three wires together at the feedpoint, and feed
them thru a 3:1 transformer.
On the other hand, if narrower beamwidth is desired, wider spacing must be
used. My phased 580 foot Beverages use 270 foot side-by-side spacing and
their performance is similar to an 1160 foot Beverage, which I do not have
room for!
73
Frank
W3LPL
donovanf@sgate.com
On Tue, 21 Oct 1997, Bill Fisher - W4AN wrote:
> > The new array ??? A phased array of 128 Beverages! Each Beverage is 220
> > feet long ( the nominal freq range is 8 MHz and up) and 4 feet high,
> > separated 4 feet from each other, with sloped ends. Grounding is extremely
>
> 4 feet of seperation? Frank can you explain more about this close
> seperation? Why did they not use less beverages with say 1/4 wave
> seperation? Please, more details!
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