[Elecraft] Ladder Line near the gutter.

[Ron D' Eau Claire]

Dan, WG4S, asked:

> I need to secure the line from wind movement anyway, so my
> question is this. How far from the metal gutter should I secure
> the line? I've not seen any literature (although I'm SURE it
> exists somewhere) as to how far to make it. I've definitely seen
> admonitions not to run the line against any metal.

The "rule of thumb" published in the ARRL handbooks  for many years was
this: "The minimum separation between either conductor and all other wiring
should be at least four or five times the conductor spacing..."

That would include any conductor or any lossy dielectric. The earth is a
very lossy dielectric. Keep the open wire line well away from it to avoid
using your r-f to warm the earthworms.

The idea is to keep the two currents in the open wire line equal and out of
phase at all points. If you accomplish that, the open wire line will not
radiate significantly. The field created by current flowing in one wire will
exactly cancel out the field in the other wire. In theory, that will only be
true of both wires are exactly in the same place - an impossible situation.
In practice, the cancellation over the HF range is excellent provided the
spacing is on the order of 2 to 6 inches (5 to 15 cm) with the narrower
spacing preferred on 28 MHz.

Feeding the open wire line from a balanced source and connecting it to a
balanced load at the antenna are two steps toward having a balanced and
out-of-phase current in each line. If you allow the line to run where one
conductor can capacitively or inductively couple to surrounding objects more
than the other conductor, you will also introduce unbalance as well as lose
r-f. So wherever you are running it, try to keep it away from objects and
keep each conductor equidistant from whatever objects you must pass close
by. Also, try to pass objects at right angles to minimize the amount of
coupling.

If you are planning on running the line at a high SWR, keep in mind that
very high voltages can exist at points along the line. Separation and
insulation are very important, not just to avoid losses but to prevent the
possibility of starting a fire in combustible material. A little dust on the
insulators holding the wires or against something they are touching and you
can have a flashover that can start a blaze. Not a happy prospect,
especially in a hidden corner of an attic.

Those high voltages are also why true open wire line, with a minimum of high
quality insulators holding the wires, is far preferable to the common
'ladder line' or, worse, 'twin lead'.  Where the wires do have to touch
something, such as the spacers holding them, you want the very best
insulation you can get.

Ron AC7AC
K2 # 1289