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Regards from Reg, G4FGQ
For Free Radio Design Software
go to http://www.g4fgq.com
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"N3UMH" wrote in message
om...
"Reg Edwards" wrote in message
...
How would
one stiffen the overall draped loop though to prevent it being blown
near metal in a breeze?

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What's the matter with metal, steel, aluminium ?

Are they not good, low-loss conductors?

No harm in running, if you must, balanced lines near to metal structures
for
a few inches.

I have seen a method which involves inductive coupling between a pair
of single turn loops. I guess the idea is that you have a loop on the
tower and a loop on the mast (possibly both self resonant to present
the proper impedance to the ladder line). You make them coplanar and
close together so that they couple to each other, and connect the
ladder line to their terminals.

This, of course, only works for monobanders...

73,

Dan, N3UMH

======================

Dan, you are quite right of course. I am incited to go further.

I was concerned with the long-lived popular misconception, plagiarised by
old wives like Yuri who have never thought about it, that running balanced
lines very near to metal structures is the worst possible thing to do
because it is 'lossy'. But nobody ever states how much more lossy it is.
(Lord Kelvin.)

In fact, if you MUST run a balanced line, even wide-open-wire stuff, near to
an expanse of some material then the metals copper and aluminium are the
best materials to run it near to. No significant extra loss occurs in the
line - the only effect at HF is a slight reduction in line Zo due to an
increase in line capacitance the length of line involved. There's no more
radiation than what occurs from the line when it is isolated in space.
Perhaps less. And as Cecil has observed, nobody knows what the Zo of
nominal 450-ohm ladder-line actually is within +/- 15 percent anyway,
although it has a serious effect on the performace of G5RV's and similar
(hopefully no tuner) multiband antennas.

The small currents induced in the adjacent 'foreign' metal run TRANSVERSELY
on the metal surface over a distance equal to the line conductor spacing and
are harmless. The other old-wives story that the line should be twisted may
in fact spoil the effect and do more harm than good. It also spoils the
cosmetics.

The usual example is when bringing an open-wire or ladder-line into the
shack. No harm occurs when bringing the line wires together for a few
inches and drawing them through a single oversize hole drilled in a steel or
aluminium window frame. A liitle more increase in insulation thicknes is
advisable for high power transmitters.

It is pointless to convert to a pair of short coaxial lines drawn through
TWO spaced holes. That causes a much larger lump of capacitance across the
line although even then, at HF, it will be harmless - equivalent to an
unnoticeable readjustment of a tuner capacitor setting.

The problem needs more thought when bringing an open-wire line through a
timber, brickwork or concrete wall. Those materials ARE lossy (dielectric
loss) and should be avoided. They may heat up when on continuous high power
with standing waves located at a voltage (not current) maximum.
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A few more icons demolished, eh Roy? ;o)
Reg, G4FGQ