Topband: Barbed Wire Fence as Beverage?

[Greg - ZL3IX]

Hi Brian,

I can see two main problems with doing this.  I haven't tried using the 
actual fence strand, but I did have a Beverage that ran close along the 
top of the fence.

Problem 1.

Being in close proximity to the other fence strands, coupling from them 
is significant, compromising the front to back ratio.  I found that I 
improved the F/B ratio from about 8 dB to about 15 dB by increasing the 
spacing between the Beverage wire and the top of the fence, from 300mm 
to 1.8m.

Problem 2.

Unless the fence is very high, the top strand is probably quite close to 
the ground.  The insertion loss of the transmission line formed between 
the strand and the ground will be significantly higher, than if the wire 
is raised up a couple of metres.  This means that currents induced at 
the far end of the wire are significantly smaller in magnitude than 
currents induced in closer parts of the wire, even thoguh they come from 
the same wave.  The spatial decorrelation effect of, say, a 300m wire, 
is then compromised, and the directivity is reduced.  I found that the 
common mode inserton loss dropped from 8 dB to 4 dB, when I increased 
the height of the wire as described above.

I achieved the height increase (and increased separation from the fence) 
by drilling holes in the tops of the fence posts, and inserting bamboo 
supports.  These have now been in place for nearly a year with no sign 
of degradation.

73, Greg, ZL3IX

On 2010-11-03 05:25, Brian Kassel wrote:
>   Can the top wire
> of the fence be insulated and used? My 3 acre property shape is very long
> and not very wide, sort of triangular shaped. I don't have enough room to
> run a a wire across the property, only lengthwise, along the fence.