[600MRG] Distance from powerline question
Rudy Severns
n6lf at epud.net
Mon Dec 8 12:47:58 CST 2014
My power line situation is pretty typical: lines along the side of my
property extending to and from infinity with periodic downleads for service
to homes in the neighborhood. Each service point has a ground wire from the
transformer to a ground stake at the base of the pole. What I'm facing is
an extensive array of vertical radiators with heavy top-loading. The noise
is coming at me over a wide arc. Narrow directional nulling doesn't buy
much!
For a short vertical the near E-field close to the radiator falls off as
1/r^3. In the case of 630m with 40'-50' high vertical radiators, the
near-field extends out to at least 1/8-wave (250') and is still noticeable
out to a 1/4-wave (500'). I have experimentally verified this using two
identical vertical voltage probes, one 200' from the lines and the second
another 200' away. Doubling the distance from the source (200' to 400') you
would expect the induced voltage to decrease by a factor of 8 (2^3) or -18
dB. I measured -15 dB.
I've been busy playing receive antenna games here but what works best is to
move the rx antenna as far as possible from the lines. For me that's about
400'. For those of you in an urban environment that's probably not
possible and there are no easy answers.
73, Rudy N6LF
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