On 7/31/2011 3:09 PM, John S wrote:
On 7/31/2011 4:02 PM, Owen Duffy wrote:

Owen

PS: hams universally ignore the guidance of NFPA 70 which makes
recommendation on conductors for antennas.

Maybe because NFPA 70 costs $150 US?

John

Free at the library, and at various sites for California Title 24.
http://rrdocs.nfpa.org/rrserver/brow...tricalCode2010

And the sections on antennas are widely quoted. I don't think cost of a
copy of the code is why hams don't follow it.

here you go:
II Receiving Equipment - Antenna Systems
Article 810.16 Size of Wire-Strung Antenna -Receiving Station
(A) Size of Antenna Conductors. Outdoor antenna conductors for
receiving stations shall be of a size not less than given in Table 810.16(A)
Table 810.16(A) Size of Receiving Station Outdoor Antenna Conductors
Minimum size of Conductors (AWG) where Maximum Open Span Length is:
Less than 11m 11m to 45m Over 45m
Al Alloy, hard
drawn copper 19 14 12

Cu Clad Steel,
Bronze, other high
strength matl 20 17 14

Or
III Amateur Transmitting and Receiving Stations - Antenna Systems
less than 45 m over 45 m
Hard drawn copper AWG 14 AWG 10
CCS, bronze, etc. AWG 14 AWG 12

On 7/31/2011 3:26 PM, Owen Duffy wrote:
John wrote in :


Maybe because NFPA 70 costs $150 US?


Yes, standards are expensive things and it is a frustration when
researching.

Anyway, NFPA makes recommendation on the wires for ham antennas
specifically, and it may be binding in some places.

I suspect the reason for ignoring it is that the advice is unaccepable
to most hams.

That said, it does seem over the top in some areas, and is hardly
comprehensive in its thinking. For example, the prescription for
feedlines seems to not be aware of the existence and use of coax.

You refer to the "continuously enclosed metallic shield", I suspect.


I guess it is these gaps that give critics the basis for arguing against
the whole thing.

Anyway, in respect of antenna wires, it does not 'permit' annealled
copper or other low strength materials, and it 'requires' a minimum
conductor diameter of #14 for up to 150' span.

They may have had in mind the risk to persons and property where low
strength conductor are broken in high wind and make contact with power
lines.


That is precisely why. (ice loads, too)

Jim Lux wrote in
:

....
III Amateur Transmitting and Receiving Stations - Antenna Systems
less than 45 m over 45 m
Hard drawn copper AWG 14 AWG 10
CCS, bronze, etc. AWG 14 AWG 12

Examples 7 and 8 in the catenary calculator at
http://vk1od.net/calc/awcc/awcc.htm use #14 and #10 HDC. Readers can
explore the survivability of wind and ice with the calculator.

If I model a 45m simple span of #14 HDC at the lowest wind speeds
applicable to the design of structures in this jurisdiction, using the
mandated safety factor, the minimum sag is about 5% of span, about as
large as it typically practical for such a span.

NFPA 70 does not apply in VK, though there are standards that apply and
the answer comes up pretty much the same, just there is more freedom in
engineering shorter spans.

Owen

Stainless steel mig welding wire.
Any reason why this won't work as a wire antenna?
Very strong, fairly cheap, but doesn't like kinks.

'I personally think Ray Davies wrote some very good songs.'

http://en.wikipedia.org/wiki/Ray_Davies

wrote in :

Stainless steel mig welding wire.
Any reason why this won't work as a wire antenna?
Very strong, fairly cheap, but doesn't like kinks.

It is small diameter, high resistivity material. If it is magnetic, even
worse.

I depends on its length, and the current flowing.

The article http://vk1od.net/antenna/conductors/loss.htm includes an
example of 316 SS MIG wire.

It is great for stealth antennas, actually doubly so, because not only is
it hard to see, it is hard to hear.


Owen

On 1 Aug,
Owen Duffy wrote:

"Sal" wrote in :

I have two 20m dipoles hanging, one with a span line and one
free-hanging. They were both temporary ... last year.

Sal, there would be those who would chide you that such an antenna
obviously wasn't big enough... in the sense that "if it didn't blow down
last season, it wasn't big enough".

And we wonder why so many housing block have restictive covenants that are
not ham friendly. We might just have bought that on ourselves to some
extent.

At one time I was working JA from yhe UK using a long wire (about 40m) of 30
swg and 100w. It didn't blow down. however it was only up for a week as a
stealth ant. currently my long wire is 1mm enameled wire, to be less
vu=isibly intrusive (and at current copper prices cheaper) than the
recommended 14 swg (12 awg).

This replaces one which failed a couple of years ago constructed with
thin insulated 5A lighting flex not much more than bell wire that had been up
nearly 30 years.

It's better using a non optimal stealth ant than none at all!

--
BD
Change lycos to yahoo to reply

On 8/1/2011 7:52 PM, Jim Lux wrote:
On 7/31/2011 3:26 PM, Owen Duffy wrote:
John wrote in :


Maybe because NFPA 70 costs $150 US?


Yes, standards are expensive things and it is a frustration when
researching.

Anyway, NFPA makes recommendation on the wires for ham antennas
specifically, and it may be binding in some places.

I suspect the reason for ignoring it is that the advice is unaccepable
to most hams.

That said, it does seem over the top in some areas, and is hardly
comprehensive in its thinking. For example, the prescription for
feedlines seems to not be aware of the existence and use of coax.

You refer to the "continuously enclosed metallic shield", I suspect.


I guess it is these gaps that give critics the basis for arguing against
the whole thing.

Anyway, in respect of antenna wires, it does not 'permit' annealled
copper or other low strength materials, and it 'requires' a minimum
conductor diameter of #14 for up to 150' span.

They may have had in mind the risk to persons and property where low
strength conductor are broken in high wind and make contact with power
lines.


That is precisely why. (ice loads, too)

NFPA (according to what you posted) requires heavier gauge wire for
transmitting than for receiving. Transmitting makes the wire weigh more?

"Owen Duffy" wrote in message
...
"Sal" wrote in :

I have two 20m dipoles hanging, one with a span line and one
free-hanging. They were both temporary ... last year.

Sal, there would be those who would chide you that such an antenna
obviously wasn't big enough... in the sense that "if it didn't blow down
last season, it wasn't big enough".

LOL

And we wonder why so many housing block have restictive covenants that are
not ham friendly. We might just have bought that on ourselves to some
extent.

I'm in a 1960s neighborhood. If anybody bitches about
antennas (nothing, yet), I will invite their attention to the old-fashioned
utility poles & wires that decorate (?) the streets. A few blocks out and a
few years later, they undergrounded the utilities.

Sal

wrote in message ...
On 1 Aug,
This replaces one which failed a couple of years ago constructed with
thin insulated 5A lighting flex not much more than bell wire that had been
up
nearly 30 years.

This got me thinking. (Dangerous, yes, but I occasionally risk it.)

Since a normal dipole has current max near the center, is there more
localized heating (I-squared-R) nearer the feed point? Seems like it ought
to be. Can you overheat a small wire and make it fail there by melting?????

No, I don't want to try it. I'm hoping somebody knows. Exciting story even
better.

"Sal"

On 7/31/2011 16:32, KD2AIP wrote:
Anyone have experience making a dipole from 18 gauge speaker wire? I
have a whole lot of it lying around the house, and was wondering if I
could put it to some good use.

Be aware that the National Electric Code (NEC); that is enforced as law
in many jurisdictions; forbids the use of wire that small for aerials of
radio stations. The NEC specifically requires that size fourteen
American Wire Gauge be the minimum size that is used.

In point of fact you are unlikely to ever get inspected unless some
neighbor is raising a stink about your antenna. The danger is that in
the event of a physical failure of the antenna that brings harm to
anyone or anything, the use of non code compliant size wire will shift
all blame on to you. That could include a trespassing neighbor kid
yanking on your coax lead in and being burned before you realized that
the antenna was in direct contact with him because the wire of the
antenna that was supporting the coax had failed. The reason that you
might be blamed for something that at first blush appears to be
outrageous conduct on the kids part is based on the idea that anything
like that which is not sufficiently guarded so as to prevent that kind
of occurrence is considered to be an attractive nuisance in the eyes of
the law.

If the wire is supported on a messenger that has at least the breaking
strength of #14 AWG wire the reasonableness standard should serve as an
effective shield against that particular approach in a law suit. Be
aware that in electrical parlance, which is what the code is written in,
messenger supported means that it is continuously supported by another
means. It does not mean that it is suspended from some stronger support
at it's ends. To be messenger supported the entire weight and the
catenary strain of the support system would have to be born entirely by
a means other than the undersized conductor itself.

I am not a lawyer nor do I play one on local cable access television.
If you need advice about the most likely legal affects of an injury that
is caused by your amateur radio equipment you might want to patronize a
law schools legal clinic. The Professors that supervise such clinics
love questions like this because they take a fair amount of effort to
answer well. What you end up with is really high quality advice
prepared under the supervision of some of the best legal minds that a
person of ordinary means could ever get access to.

I've quoted the sections of the NEC which are applicable to antenna
conductor size below. Be aware that the NEC contains many more
provisions covering amateur radio stations specifically. It is worth
your time to obtain the use of the edition of the NEC that is adopted
for enforcement in your community and check your installation against
the provisions of the code.

--
FWIW YMMV
Tom Horne, W3TDH

"ARTICLE 810 Radio and Television Equipment
I. General
810.1 Scope.
This article covers antenna systems for radio and television receiving
equipment, amateur radio transmitting and receiving equipment, and
certain features of transmitter safety. This article covers antennas
such as multi-element, vertical rod, and dish, and also covers the
wiring and cabling that connects them to equipment.

810.11 Material.
Antennas and lead-in conductors shall be of hard-drawn copper, bronze,
aluminum alloy, copper-clad steel, or other high-strength,
corrosion-resistant material.
Exception: Soft-drawn or medium-drawn copper shall be permitted for
lead-in conductors where the maximum span between points of support is
less than 11 m (35 ft).

810.12 Supports.
Outdoor antennas and lead-in conductors shall be securely supported. The
antennas or lead-in conductors shall not be attached to the electric
service mast. They shall not be attached to poles or similar structures
carrying open electric light or power wires or trolley wires of over 250
volts between conductors. Insulators supporting the antenna conductors
shall have sufficient mechanical strength to safely support the
conductors. Lead-in conductors shall be securely attached to the antennas.

810.13 Avoidance of Contacts with Conductors of Other Systems.
Outdoor antennas and lead-in conductors from an antenna to a building
shall not cross over open conductors of electric light or power circuits
and shall be kept well away from all such circuits so as to avoid the
possibility of accidental contact. Where proximity to open electric
light or power service conductors of less than 250 volts between
conductors cannot be avoided, the installation shall be such as to
provide a clearance of at least 600 mm (2 ft).

Where practicable, antenna conductors shall be installed so as not to
cross under open electric light or power conductors.

[One of the leading causes of electrical shock and electrocution,
according to statistical reports, is the accidental contact of radio,
television, and amateur radio transmitting and receiving antennas and
equipment with light or power conductors. Extreme caution should
therefore be exercised during this type of installation, and periodic
visual inspections should be conducted thereafter. ] This is explanatory
material from the NEC Handbook and not part of the NEC.

810.14 Splices.
Splices and joints in antenna spans shall be made mechanically secure
with approved splicing devices or by such other means as will not
appreciably weaken the conductors.

[Conductor spans from antennas should be of sufficient size and strength
to maintain clearances and avoid possible contact with light or power
conductors. Splices and joints should be made with approved connectors
or other means that provide sufficient mechanical strength so that
conductors are not weakened appreciably, a condition that could cause
them to break and come into contact with higher-voltage conductors.]
This is explanatory material from the NEC Handbook and not part of the
NEC.

810.15 Grounding.
Masts and metal structures supporting antennas shall be grounded in
accordance with 810.21.

810.52 Size of Antenna.
Antenna conductors for transmitting and receiving stations shall be of a
size not less than given in Table 810.52.

Table 810.52 Size of Amateur Station Outdoor Antenna Conductors
Material Minimum Size of Conductors (AWG)
Where Maximum Open Span Length Is
Less Than 45 m (150 ft) Over 45 m (150 ft)
Hard-drawn copper 14 10
Copper-clad steel, bronze, or other high-strength material
14 12

810.53 Size of Lead-In Conductors.
Lead-in conductors for transmitting stations shall, for various maximum
span lengths, be of a size at least as great as that of conductors for
antennas as specified in 810.52." Copyright 2002 the National Fire
Protection Association.