[Elecraft] Antenna feedline Placement

[Ron D'Eau Claire]

The usual "rule of thumb" that I've seen is to keep open wire (ladder, =
twin,
etc) from 4 to 6 times the spacing of the wires away from other objects, =
as
a minimum. The idea is that, if the feeders are "balanced" (have equal =
and
opposite RF currents flowing along each conductor) the "net" RF field at =
an
appreciable distance from them will be zero. That is, they don't =
"radiate"
RF or pick up external RF energy.

Ideally, you'd have both conductors in the "open wire" line in exactly =
the
same space. Since we can't do that without having them shorted =
electrically,
we separate them. As long as the separation is a very small fraction of =
a
wavelength, the effect of separating them will be very small and the
cancellation of the external RF field will be very good. That's why
parallel-conductor or "open wire" line designed for VHF, like TV =
twinlead,
has a rather narrow spacing while open wire line for HF works very well =
with
much wider spacing. (The spacing and diameter of the conductors effect =
the
impedance of the line as well). But the cancellation depends upon having =
the
RF fields interact only with each other across the gap between the =
wires,
with nothing nearby influencing them.=20

IF balance is important and you must have the coax running parallel to =
the
open wire line, at least arrange things so the conductors in the open =
wire
line are held equidistant from the coax to the effect on the RF field =
around
each wire will be nearly the same as possible.=20

Note that very often balance in open wire feeders is not important, =
since
the antenna itself isn't balanced or, as in the case of contemporary =
Windom
antennas, much of the antenna system performance is gained because the
feeders are NOT balanced so they will radiate. Whether your loop is =
balanced
depends upon a lot of factors in the design and placement of the loop
itself.

Ron AC7AC

-----Original Message-----
Jim Corbitt wrote:

> Is it OK to put 2 feedlines adjacent to each other to get outside to=20
> the antennas?  One feedline is ladder line and the other is RG-8 coax. =
=20
> One will go to a loop antenna and the other to a dipole.  Is it OK to=20
> put the earth ground for the rig through the same opening? I was=20
> thinking of routing  a plastic pipe  through the basement wall and up=20
> the side of the house for sort of a conduit to put the
> feedlines in.   Would it be better to use a metal conduit?