OK, let's discuss dipoles vs length
 

On 10/12/2014 2:05 PM, wrote:
John S wrote:
On 10/12/2014 1:06 PM, wrote:
Lostgallifreyan wrote:
John S wrote in :

Something else might be interesting; include the effects of sag
(centenary) in a wire antenna.

Agreed. I was thinking about that possibility last night. Meaning 'catenary',
perhaps? As in 'hanging chain'? I doubt any longwire would lack this, so
modelling it would be useful.

I doubt you will see any significant difference.


Do you have any data or a simulation which supports your position?

(snip irrelevant portion)

Reread the portion you snipped as irrelevant.

My mistake. I see what you mean.

OK, let's discuss dipoles vs length
 

"Lostgallifreyan" wrote in message
. ..
"Ralph Mowery" wrote in
:

Looking at a chart in an old ARRL antenna handbook gives a rough
estiment of a length of 500 feet and a tension of 400 pounds a wire of
around 12 to 14 gauge will drop about 10 feet if Idid it right.


That's useful. Thanks. Did they say what metal it was? I'm guessign hard
drawn copper but if not it may be harder to adjust reckoning for something
else.

They gave two types. Hard drawn copper and copper coated steel. The only
differance would be the weight of the wire and how much tension you can put
on the wire before reaching the breaking point. The type of wire does not
matter, just the weight and how much tension you can put on it before it
breaks. Really how much tension you can put on the wire with a large safety
factor. Probaly less than half its actual breaking tension. I know that
Rohn towers specifies about 10 % for their guy cables. That is for the 4000
breaking of 3/16 cable they recommend 400 pounds of tension on the guy
cables.

Here is an on line calculator that will give you the answer to your
question.
http://www.spaceagecontrol.com/calccabl.htm

It seems for the first part you devide the tension of the wire by the number
of feet between supports.
For the 3rd part you devide the total weight of the wire by the length.




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OK, let's discuss dipoles vs length
 

On 10/13/2014 10:12 AM, Ralph Mowery wrote:
"Lostgallifreyan" wrote in message
. ..
"Ralph Mowery" wrote in
:

Looking at a chart in an old ARRL antenna handbook gives a rough
estiment of a length of 500 feet and a tension of 400 pounds a wire of
around 12 to 14 gauge will drop about 10 feet if Idid it right.


That's useful. Thanks. Did they say what metal it was? I'm guessign hard
drawn copper but if not it may be harder to adjust reckoning for something
else.

They gave two types. Hard drawn copper and copper coated steel. The only
differance would be the weight of the wire and how much tension you can put
on the wire before reaching the breaking point. The type of wire does not
matter, just the weight and how much tension you can put on it before it
breaks. Really how much tension you can put on the wire with a large safety
factor. Probaly less than half its actual breaking tension. I know that
Rohn towers specifies about 10 % for their guy cables. That is for the 4000
breaking of 3/16 cable they recommend 400 pounds of tension on the guy
cables.


That is STATIC tension - that is, when no wind is blowing. Tension
increases significantly when there is a wind. Rohn tower specs are
designed to withstand winds of 85mph, IIRC (I last did commercial tower
work in 1972 or so, so I don't remember the exact specs). At that wind
they have maybe a 50% safety margin. Still significant for new cable,
but when your guys are 25 years old, the tower should still withstand
that wind.

And yes, some of the towers I put up over 40 years ago are still
standing. But I'm sure they've had some maintenance since that time.

--
==================
Remove the "x" from my email address
Jerry, AI0K

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

OK, let's discuss dipoles vs length
 

"Jerry Stuckle" wrote in message
...
On 10/13/2014 10:12 AM, Ralph Mowery wrote:
"Lostgallifreyan" wrote in message
Rohn towers specifies about 10 % for their guy cables. That is for the
4000
breaking of 3/16 cable they recommend 400 pounds of tension on the guy
cables.


That is STATIC tension - that is, when no wind is blowing. Tension
increases significantly when there is a wind. Rohn tower specs are
designed to withstand winds of 85mph, IIRC (I last did commercial tower
work in 1972 or so, so I don't remember the exact specs). At that wind
they have maybe a 50% safety margin. Still significant for new cable,
but when your guys are 25 years old, the tower should still withstand
that wind.

And yes, some of the towers I put up over 40 years ago are still
standing. But I'm sure they've had some maintenance since that time.


Yes, static tension. I was thinking along the same line for the wire
antenna. YOu only want to put a fraction of the breaking tension on the
wire to allow for the wind and if on a swaying support like a tree.

Rohn 25g is specified for several differant wind speeds. Probably with
difffrant ammounts of antenna surface area. Sometimes either more or larger
guy wires are used.
I put a 60 foot tower up for myself about 10 years ago and it is still up.
Don't think we had any 75 mph winds, but could have during the gusts. I
tried to meet their specs or beter when I put it up. I know a couple of
local hams that over the years did not put them up to what I would have
thought was to specs and then came down.



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OK, let's discuss dipoles vs length
 

On 10/13/2014 9:12 AM, Ralph Mowery wrote:
"Lostgallifreyan" wrote in message
. ..
"Ralph Mowery" wrote in
:

Looking at a chart in an old ARRL antenna handbook gives a rough
estiment of a length of 500 feet and a tension of 400 pounds a wire of
around 12 to 14 gauge will drop about 10 feet if Idid it right.


That's useful. Thanks. Did they say what metal it was? I'm guessign hard
drawn copper but if not it may be harder to adjust reckoning for something
else.

They gave two types. Hard drawn copper and copper coated steel. The only
differance would be the weight of the wire and how much tension you can put
on the wire before reaching the breaking point. The type of wire does not
matter, just the weight and how much tension you can put on it before it
breaks.

(snip)

My recollection is that copper-coated steel should not be used below a
frequency where the skin depth is less than a few times the copper
coating thickness. So, there is a minimum frequency vs copper thickness.

OK, let's discuss dipoles vs length
 

On Mon, 13 Oct 2014 03:48:29 -0500, Lostgallifreyan
wrote:

when I see a Smith chart or other diagram indicating relative
signal transmission strength at some distance and direction,

A Smith Chart is a transmission line matching tool and has nothing to
do with distance, range, direction, and strength of an RF signal.
Reading between the lines, you might be referring to an antenna
pattern polar graph, which sorta looks like a Smith Chart while one is
under the influence of controlled substances.

does this follow
the rule of many 'simple' transducers, in that the same chart exactly models
the sensitivity of the same antenna for reception?

Antennas do not have a sensitivity spec. That's in the receiver. All
antennas do is direct the RF in some particular direction, sometimes
concentrating it, which is called gain. Antennas do not produce,
amplify, or "strengthen" RF. The only re-direct it.

I think you might need some help in basic RF buzzwords. It's helpful
when we're both using the same terms to discuss the same phenomenon.
Google finds several RF glossary lists online. Start with "A" and
work your way to "Z" trying to absorb and understand as many buzzwords
as possible. I do that when I initially approach a new technology and
recently had to do it for optical terminology, of which I know little.
If successful, we might then be able to decode what you're asking.
http://micro.apitech.com/glossary.aspx
http://e-meca.com/tech_papers/glossary.php
http://www.amphenolconnex.com/support/glossary

I'm hoping it does,
otherwise life might get complicated. :)

Hope is a poor substitute for understanding.
Hit the books and enlightenment will hopefully follow.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

OK, let's discuss dipoles vs length
 

On 10/13/2014 10:42 AM, Ralph Mowery wrote:
"Jerry Stuckle" wrote in message
...
On 10/13/2014 10:12 AM, Ralph Mowery wrote:
"Lostgallifreyan" wrote in message
Rohn towers specifies about 10 % for their guy cables. That is for the
4000
breaking of 3/16 cable they recommend 400 pounds of tension on the guy
cables.


That is STATIC tension - that is, when no wind is blowing. Tension
increases significantly when there is a wind. Rohn tower specs are
designed to withstand winds of 85mph, IIRC (I last did commercial tower
work in 1972 or so, so I don't remember the exact specs). At that wind
they have maybe a 50% safety margin. Still significant for new cable,
but when your guys are 25 years old, the tower should still withstand
that wind.

And yes, some of the towers I put up over 40 years ago are still
standing. But I'm sure they've had some maintenance since that time.


Yes, static tension. I was thinking along the same line for the wire
antenna. YOu only want to put a fraction of the breaking tension on the
wire to allow for the wind and if on a swaying support like a tree.

Rohn 25g is specified for several differant wind speeds. Probably with
difffrant ammounts of antenna surface area. Sometimes either more or larger
guy wires are used.
I put a 60 foot tower up for myself about 10 years ago and it is still up.
Don't think we had any 75 mph winds, but could have during the gusts. I
tried to meet their specs or beter when I put it up. I know a couple of
local hams that over the years did not put them up to what I would have
thought was to specs and then came down.



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When I was doing it, we were putting up 150' towers. These towers were
guyed eery 35'. The biggest job was the concrete for the baseplate and
anchors - it would take use 2-3 days to dig those, depending on how hard
the ground was. But once those were in, it took us two days to put up
the tower, install the antenna (typically VHF Hi-band; this was the
early 70's, after all) and run the coax.

These towers were typically on high hills, often leased land from a
farmer. In Iowa, it's not at all unusual to get 75mph winds in the
summer thunderstorms on top of the hills. But they stayed up.

I was smart and got out of it in one piece. The first guy I worked for
fell from 60' up and broke his back on a guy wire. He was paralyzed
from the waist down. The second guy I worked for was working on a
platform at 425' and got pulled over the side while trying to lower a
beacon light (those things are heavy). Unfortunately, that day his wife
was the ground crew.

I enjoyed the work - you can't imagine the view from 1800' up a TV
tower. But I'm glad I'm not doing it any more.

--
==================
Remove the "x" from my email address
Jerry, AI0K

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

OK, let's discuss dipoles vs length
 

Lostgallifreyan wrote:
Stephen Thomas Cole wrote in
:

And the BBC TV series from the early 80s is
superior to the 2005 film in every way.

I never even knew about that one! Weird..

I have it all on VHS from way back when. Watched it again a few months ago,
still brilliant.

You've both just convinced me to
try the books again though, assuming I can still cope with reading the
printed text.

I do believe that Douglas Adams recorded unabridged (or maybe abridged?)
audiobook versions of the books. Really quite nice to hear them being read
out loud by the great man himself. Worth tracking down.

--
Stephen Thomas Cole // Sent from my iPhone

OK, let's discuss dipoles vs length
 

On 10/13/2014 11:44 AM, John S wrote:
On 10/13/2014 9:12 AM, Ralph Mowery wrote:
"Lostgallifreyan" wrote in message
. ..
"Ralph Mowery" wrote in
:

Looking at a chart in an old ARRL antenna handbook gives a rough
estiment of a length of 500 feet and a tension of 400 pounds a wire of
around 12 to 14 gauge will drop about 10 feet if Idid it right.


That's useful. Thanks. Did they say what metal it was? I'm guessign hard
drawn copper but if not it may be harder to adjust reckoning for
something
else.

They gave two types. Hard drawn copper and copper coated steel. The
only
differance would be the weight of the wire and how much tension you
can put
on the wire before reaching the breaking point. The type of wire does
not
matter, just the weight and how much tension you can put on it before it
breaks.

(snip)

My recollection is that copper-coated steel should not be used below a
frequency where the skin depth is less than a few times the copper
coating thickness. So, there is a minimum frequency vs copper thickness.


A good rule of thumb. But even at 1Mhz, the skin depth is about 66
micrometers (and falls with the square root of the frequency - at 10Mhz
it's about 21 micrometers). Cladding over a ferromagnetic material
increases the skin depth slightly, but we're already talking pretty
small figures here,.

Where it DOES come into play is when you run DC through the coax, also.
For instance, this is common in the satellite TV arena, where DC is fed
over the coax to power a preamp at the antenna. There you need to use
solid copper. But for most ham use, copper clad will work just fine, as
long as you stay within the power rating of the coax.

One side note. Copper clad anything is not certified for any ethernet
cables. Even though ethernet runs at very high frequencies, only solid
or stranded copper is acceptable.

Normally I don't recommend Wikipedia for technical discussions, but
http://en.wikipedia.org/wiki/Skin_effect is a pretty good article on it
and explains it much more clearly than my old physics textbooks did.

--
==================
Remove the "x" from my email address
Jerry, AI0K

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

OK, let's discuss dipoles vs length
 

Stephen Thomas Cole wrote in
:

I do believe that Douglas Adams recorded unabridged (or maybe abridged?)
audiobook versions of the books. Really quite nice to hear them being read
out loud by the great man himself. Worth tracking down.


I'll definitely try to find those if they're unabridged. :) I think you're
right one way or the other, he liked to try each new medium he could.