[Lowfer] Distance from powerline question - Answered

[Douglas D. Williams]

Andy, given your proximity to power lines, I definitely think a small
active loop would be something worth trying. You can experiment with
placing it in different locations on your property to find the most noise
free location. You might also be able to use the loop's nulls to your
advantage. Do you still have that Wellbrook loop I sent you? It can be a
good performer.

A common mode choke might also help, when placed between an active
antenna's dc coupler and the antenna. On the advice of Jack from Clifton
Labs I constructed one by gluing together five 40T1417-10H cores and
wrapping as many turns of RG-174 as I could fit through them. I just put
this inside the shack between the dc coupler and the antenna.

https://dl.dropboxusercontent.com/u/33457409/LF%20common%20mode%20choke.jpg

Good luck. Man made noise seems to be the biggest problem that most of us
face on LF.

D. KB4OER

On Tue, Dec 9, 2014 at 1:02 AM, Andy - KU4XR via Lowfer <
lowfer at mailman.qth.net> wrote:

> It was requested that I forward Rudy's comments from the 600 meter list to
> the lowFER
> list.. Happy to do so.. Here is Rudy's comments.. 73 : - Andy
> ______________________________________________________________________
>
> 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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