Charlie, you did not mention what kind of an array you were planning. The
answer would be very different with a simple cardioid array or 4-square as
compared to a wide spaced BSEF type array. You also did not mention the length
of the wire fence and if it was insulated and possibly close to some resonance
near the operating frequency.
The higher the RDF of an array which most times comes right along with
medium to high Front to back, the more sensitive the array will be to nearby
objects. I did some extensive testing last year in an effort to quantify this
very question. Frankly there are too many variables to provide an answer much
more than a guess. What I have found is that if you can simulate the nearby
wires or even objects in Eznec and you can get a feel for your particular
situation. You might also consider your transmit antenna as a source of
unwanted coupling as well. One of my best high performance arrays can "see"
affects from my TX vertical when modeled at over 700 feet away. It has to be
detuned during RX.
I think you can still download W8JIs rxvrhat eznec 20 foot element model
on his site. I also think to get a reasonable answer to your question you would
have to model the entire array however and then place objects such as fence
wires and possibly use a slightly elevated radial near one element to simulate
the buried element. Buried radials do couple to other objects in RX arrays.
Aside from all that my gut reaction from all my work last year is that if
you are building the 8 element circle array you are going to see a significant
problem and it is going to come from the nearby radial coupling and likely not
the top loading wire unless it is very parallel to the fence. If the fence is
grounded every few feet I think the affect will be much less and will then
manifest itself as a slight skewing of the pattern and slight reduction of RDF
due to some extra signal coupling and signal phase shifting in the close
elements received signal. Personally I would skew any radials away from or at
least perpendicular to the fence on that nearby element.
I would really encourage you to try to model this situation. I finally
modeled all the power lines, irrigation pipes, telephone wires, buildings, and
etc for my RX situation. I was amazed as to all the things coupling to vertical
arrays and even Beverages. It was also important to vary the length of the
modeled objects like power lines as they mostly were of indeterminate length so
I assumed whatever was average or even worst. My biggest surprise was the local
power drop with ground rod that looked remarkably similar to an inverted L on
160.
My 2 cents or .005 gallons Lee K7TJR Oregon
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