Grant,
Thanks for the modelling and the insulator idea. I'd suspect one
might be able to tweak the lengths between insulators to find a
"non-resonant" length on both 160/80 to minimize the impact of a
multi-strand barbed wire fence but as you suggest chain link or
welded mesh ("hogwire") fences could be an issue.
In my case, I'm looking at a variation of KB7GF's "cross-coupled
shared apex array loop" that will fit in a 100' diameter circle
with performance comparable to a 1000' Beverage and 60 degree
switching. Building it is probably next fall's project since I
have a wooded area that would hide it nicely.
73,
... Joe, W4TV
On 2015-02-03 5:11 PM, Grant Saviers wrote:
I did a quick EZNEC Pro/4 analysis of a Beverage over a 3 strand barb
wire fence, strands at 4,3,2' and antenna at 10'. I've had one that
sorta worked, now I know why.
600' of fence under 600' of antenna yields a substantially degraded F/B
(what I experienced).
2400' of fence under 600' of antenna yields a substantially vertical
pattern
Insulator breaks of the 600' of the 3 strands every 200' yielded a
1.8Mhz pattern almost the same as no fence. Adding a single strand of
continuous single fence out 600 to 1200' past both ends of the Beverage
had minimal pattern change. At 3.5 and 7 Mhz the pattern looses a bit
of F/B but is tolerable IMO.
So for a few insulators, a Beverage works over a barb wire fence.
Porcelain eggs would probably be the best bet for the strength needed.
Chain link and welded mesh fences are best avoided unless it is worth
the work to insulate sections.
Grant KZ1W
On 2/3/2015 12:52 PM, Joe Subich, W4TV wrote:
Pat,
8 to 10 feet above the barbed wire fence would be your only chance if
you are to use the existing fence lines. I would strongly suggest
reading some (all) of the references you have been offered -
particularly those that include long term experiments.
My information has simply been gathered from the reports of others over
nearly 40 years and confirmed by the performance of the few simple
Beverages I've been fortunate enough to use at various times.
The general consensus has been not to use a "ground wire" under a
Beverage or run it along above/parallel to a conductive wire fence.
Maintain at least 45 degrees and try, if at all possible, to cross
other antennas/conductive objects at right angles.
snip...
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