Rick,
A few ideas in response to your query...
I do not use multiwire Beverages, but you will probably get additional
comments on this topic.
First, I don't think a metal fence will affect a Beverage so badly that
you need to keep 200 feet away. Many measurements on adjacent Beverage
antennas indicate that separation at least equal to their height above
ground (eight foot separation for Beverages eight feet high) is adequate.
more is beeter, but 200 feet separation to a fence line should not be
necessary.
The issue with the feedline is mostly isolation of signals flowing
on shield from the ground terminating the feedpoint of the
Beverage. Any signals induced onto the shield will cause current to flow
in the ground system, which then create a voltage in series with the
signals coming off the Beverage. There are several steps to minimize
these undesired shield currents. You do N O T need to incorporate all
of these steps, many successful systems use none!
- Bury the feedline (usually impractical!)
- Use an excellent ground (multiple ground rods with B U R I E D wires
interconnecting them
- A matching transformer design with inherently good isolation from
currents on the feedline shield
- Isolate the feedline shield from the matching transformer with ferrite
beads
- Install a second ground rod -- isolated from the transformer -- to
ground the shield. Some even uise a third ground rod ten ot
tweenty feet down the feedline.
Good luck!
73
Frank
W3LPL
donovanf@sgate.com
On Wed, 8 Oct 1997, Richard Karlquist wrote:
> I have been reading up on Beverage antennas, but have not seen much
> about proper routing of the feed line to the Beverage. I gather that
> you obviously don't want to run it directly underneath and parallel to the
> antenna, but can it be in parallel and spaced away some distance? I
> read that the antenna should be 200 feet away from wire fences. Is
> this also true for coax, or can it be closer that 200 feet due to being
> on the ground? I have seen a technique where a 2 wire beverage is used
> with transformers at the end so you can run the coax from either end and
> utilize both directions. Is this technique in general use or is it too
> temperamental (or unnecessary)? Can the deleterious effects of coax be
> mitigated by inserting choke coils in the coax at regular intervals to
> prevent currents from flowing on the outside of the shield? What spacing
> would be needed?
>
> Rick Karlquist
> N6RK
> rick@area.com
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