Antenna wire
 

On Thu, 24 Aug 2006 10:05:37 GMT, Owen Duffy wrote:

There is no explicit discussion of wind loading, and the design guides
(tables, nomographs, text) lead the reader to a design based on
weight loading alone and with a Safety Factor of 10 or 5 depending on
the chosen tension.

Hi Owen,

Consult:
http://www.iaei.org/subscriber/magaz...other_code.htm

73's
Richard Clark, KB7QHC

Antenna wire
 

Richard Clark wrote:

On Wed, 23 Aug 2006 02:18:21 GMT, Owen Duffy wrote:



Apart from the challenge of making reliable connections to aluminium,
are there other "issues" that come to mind in using such wire for
antennas?



Hi Owen,

I've used ordinary house wiring for long-wires and they have survived
100# limb falls that ripped out my matching box from its post. The
survival was with the wire, not the box.

[warning to Reggie, the prose that follows contains literary
allusions]
What price tensile strength?

The worst thing you can do is pull a wire tight in an attempt to
totally eliminate sag. The inverse sine angle of its depression
magnifies the stress by huge amounts. A slight sag will never yield a
tensile failure in the most pedestrian of wire.

73's
Richard Clark, KB7QHC


As long as gravity exists will it ever be possible to get a perfectly
horizontal dipole? In spite of a strong tensile component there will
always be a vertical component due to gravity (with a centre feed there
will also be the weight of any cable and perhaps a balun as well). The
net effect is a sag called a catenary. Granted an infinite tension on
the antenna wire would probably overcome the vertical component but the
wire might not survive. The question for this relative neophyte is,
what effect does the sag have on antenna performance?

--
Paul S. Hinman - VE6LDS
long West 113 deg 27 min 20 sec
lat North 53 deg 27 min 3 sec
Maidenhead Locator DO33gk

Antenna wire
 

Paul Hinman wrote:

REDACTED

As long as gravity exists will it ever be possible to get a perfectly
horizontal dipole?

NOPE!, At least not in wire. Theoretically, not in beams either.

In spite of a strong tensile component there will
always be a vertical component due to gravity (with a centre feed there
will also be the weight of any cable and perhaps a balun as well). The
net effect is a sag called a catenary. Granted an infinite tension on
the antenna wire would probably overcome the vertical component but the
wire might not survive. The question for this relative neophyte is,
what effect does the sag have on antenna performance?

Most likely less effect than nearby objects like houses, trees, earth, moon,
sun, and rain. :-)

"How many pins can be placed on the head of an angel?" makes more sense than
hypothesizing about the effect of catenary on wire antennas.

Antenna wire
 

Paul Hinman wrote:
The question for this relative neophyte is,
what effect does the sag have on antenna performance?

For average dipoles, the ham on the receiving end
will probably not be able to tell any difference.
--
73, Cecil http://www.qsl.net/w5dxp

Antenna wire
 

On Sat, 26 Aug 2006 09:39:46 GMT, Paul Hinman
wrote:

As long as gravity exists will it ever be possible to get a perfectly
horizontal dipole?

Hi Paul,

If you read my further responses to Owen, you find the discussion of
catenaries. In that regard, the answer to your question is
unquestionably YES!

You merely need to provide a catenary supporting the perfectly
horizontal dipole. Regard any suspension bridge to discover the
mechanics of construction. And, yes, the road bed is not horizontal,
but an arc built to anticipate load; the ingenious antenna builder can
reconcile this (trolley systems across the world with overhead
suspended wires solve this easily).

The question for this relative neophyte is,
what effect does the sag have on antenna performance?

Barring the suspension method, and the wire sags, it becomes a
question of how much, and more importantly, in what relation to
ground? If you have a 160M dipole with the ends up 10 meters, and a
sag of only 0.1°, then you still have a dog. If it is a 10M dipole
with a 10° sag, then you have a performer. This is a 100 fold
variation that would seem to invert expectations - if were not for the
wavelength and relation to ground.

73's
Richard Clark, KB7QHC

Antenna wire
 

On Sat, 26 Aug 2006 09:39:46 GMT, Paul Hinman
wrote:


wire might not survive. The question for this relative neophyte is,
what effect does the sag have on antenna performance?

Yes, perhaps you got on the wrong tram in the discussion about sag. It
would be easy if you hadn't read the entire thread.

Low sag is obtained by high wire tension.

High wire tension under static conditions increases the risk of
breaking under wind loading.

Antennas that have broken don't perform so well.

Owen

PS: In answer to your question as to whether a dipole can ever be
perfectly horizontal, perhaps no, perfect is probably not achievable
by any real thing, but yes, it can be done to a close approximation,
but it is probably not practical in most situations. Think of an
electric railway with overhead power, the power conductor is very
close to constant grade and parallel to the tracks, think of
suspension bridges with an approximately flat roadway. There are of
course other solutions as well.

--