OK, let's discuss dipoles vs length
 

In message ,
writes




60 feet is good for 30M, marginal for 40M, and crap for 80M and below
for a dipole.

It is also too high for 15M and up.

For best results, a diple should be at .5 labda.

Then again, a marginal 40M dipole is better than no antenna at all.

Regardless of the theory, in real life (with real-life ground
conductivity/reflectivity, and the prevalence of nearby clutter and
obstruction), I can't help feeling in my water that 'higher generally
works better'!!



--
Ian

OK, let's discuss dipoles vs length
 

On Sun, 12 Oct 2014 12:03:43 -0500, John S
wrote:

Excellent! I like to explore and I encourage everyone to do so whether
it be with math tools or getting your hands dirty. Keep it up.

This might be useful:
http://www.amanogawa.com
Java required. Among the "Linear Antenna" animations is a common
dipole model, which shows the effects of different element lengths:
http://www.amanogawa.com/archive/DipoleAnt/DipoleAnt-2.html
I think (not sure and too lazy to RTFM) that "directivity" means gain
linear gain.

More NEC modeling tools:
http://wb0dgf.com/nec-mininec.htm

I'm partial to 4NEC2.
http://www.qsl.net/4nec2/
It comes with a huge collection of sample antennas suitable for
analysis and plagiarizing. Most of my stuff was done with 4NEC2:
http://802.11junk.com/jeffl/antennas/
(Not everything shown is my work). There are plenty of tutorials on
the web and videos on YouTube showing how to get started with 4NEC2.
https://www.youtube.com/results?search_query=4nec2
There is also a multi-threaded engine for speeding up 4NEC2. Highly
recommended:
http://users.otenet.gr/~jmsp/

If you are into reverse engineering commercial and ham antennas to see
how they work, there are a number of collections online.
http://www.hdtvprimer.com/ANTENNAS/comparing.html
http://www.hdtvprimer.com/SIMS/
http://www.qsl.net/kp4md/modeling.htm
http://www.arrl.org/antenna-modeling-files
If you want to go Googling for .NEC files, try something like this:
https://www.google.com/#q=filetype:nec+antenna
https://www.google.com/#q=filetype:ez+antenna
Some of the commercial antennas I've modeled turned out to be not very
good such as this 2.4GHz yagi:
http://802.11junk.com/jeffl/antennas/mfj1800/
(Hint: It's a 200 ohm feed, not 50 ohms).

One important "trick" is to always run an average gain test on your
design. This is a sanity check to make sure your model somewhat
resembles reality. There are at least two examples of antennas on my
web pile that do NOT pass this test and are therefore impressive
looking garbage. The results should be 1.0 for most antennas.
http://fornectoo.freeforums.org/run-average-gain-test-t355.html
http://www.arrl.org/files/file/Antenna%20Modeling%20for%20Beginners%20Supplementa l%20Files/EZNEC%20Modeling%20Tutorial%20by%20W8WWV.pdf

Please do NOT get hung up on using just one modeling program. While
the others have different interfaces and file formats, they are often
better at doing specific things. For example, I use several yagi
design programs to generate the dimensions and an NEC2 deck. I then
use EZNEC or 4NEC2 to more closely look at the result, and to add
support structures, real grounds, tapered elements, etc. While you
can buy programs that will do it all, you don't want to know the
price.

Testing antennas is also somewhat of an art. A pile of test equipment
is always nice:
http://802.11junk.com/jeffl/pics/home/slides/test-equip-mess.html
For the price of an HF radio, you can buy various "antenna analyzers"
and "network analyzers[1]" that will do a good job of emptying your
bank account. Being cheap, I just use a "return loss bridge", RF
sweep generator, and an oscilloscope. The RLB can be easily built.
These are nice:
http://www.wb.commufa.jp/ja2djh/html/e_rlb.html
Mine are ugly so no photos. There's not much to it. Just plan on
blowing out a few diodes:
http://www.qsl.net/n9zia/wireless/appendixF.html#11
http://www.qsl.net/n9zia/wireless/pics/rtrn_loss_bridge.png
What limits an RLB is that it only shows VSWR or return loss. There's
no indication if the antenna is capacitive or inductive. That's not a
real limitation as your radio could care less if the 50 ohms it sees
is resistive, capacitive, inductive, or a combination of these, as
long as the conglomeration works out to 50 ohms.

The bad news is that the RLB has to be near the antenna feed point in
order to get useful results. That usually means climbing the tower.
You can try using it at the xmitter end of the feed line, but I don't
recommend it. I recommended to one former friend how to install a
coax switch at the feed point, with one port going to an RLB. That
worked splendidly until just after he applied 500 watts to the
antenna, and fried the RLB diode. Make sure the switch has sufficient
isolation and that the RLB input is shorted when not in use.

The sweep generator is probably the most expensive part of the puzzle.
The frequency range you want to cover is always important. The HF
range is covered nicely by cheap DDS (direct digital synthesizer)
modules found all over eBay. For example:
www.ebay.com/sch/i.html?_nkw=dds+module
Add a PIC controller and output amplifier, and you have a sweeper. Or,
just buy one:
http://www.ebay.com/itm/121362216469
One problem with these is that they don't have frequency markers, but
that can be added later. For VHF and UHF, commercial equipment is
probably best. If you can find cable TV test equipment, it will
usually get you to about 400 MHz. That's three HP8620 sweepers in the
pile on the left, none of which work perfectly:
http://802.11junk.com/jeffl/pics/home/slides/BL-shop5.html

For the oscilloscope, you'll need something that is DC coupled. That
eliminates most PC sound card based software. For running an RLB, a
cheap 2.0 MHz DSO (digital storage scope) works just fine. The tiny
pocket size scopes found all over eBay will work, but the screens are
too small to see any detail. That might work if you can unload screen
captures to a computah and/or printer.

That leaves the question of why bother modeling when you can just
cut-n-try an antenna until it works? If you want to make one of
something, cut-n-try is a very good and efficient way of getting one
of anything to work. However, if you're planning on making more than
one, or publishing your design for others to copy (or steal), then
some clues as to the theoretical possibilities of the design are going
to be needed. A few years ago, I worked on a UHF antenna that was
sufficiently high in gain, and therefore narrow band, that customers
had to order it by the frequency of operation. I beat the NEC2 model
to death until everything possible was thrown into the model. U-bolts,
mounting hardware, pipes, yard arms, screws, nearby power wires, other
antennas, vehicles, buildings, etc. It was massive overkill, but very
necessary. When field tests were run on the first few installs, the
measured radiation patterns and return loss graphs were perfect. You
can't do that without a computah model.



[1] Incidentally, I've seen this problem a bit too often with MFJ
antenna analyzers and some VNA's.
http://802.11junk.com/jeffl/MFJ-269-repair/
If you own an MFJ analyzer, I suggest you stock up on matched diodes
for the inevitable rebuild.

--
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 10/12/2014 2:59 PM, Lostgallifreyan wrote:
John S wrote in :

I know of Hitch-Hiker's Guide To The Galaxy, but I have never watched.
Probably my loss.

Not really. :) It's much better read, or maybe best of all, heard in the
original programs that went out on Radio 4 in the early evenings in the late
70's. Those are famous, likely easily had in various ways. I've seen the
movie, but it doesn't work for me so well. Some of it is great, but they
totally failed to get Marvin right, and that means they lost a lot of the
depth of it. I liked their Vogons though.


I prefer the book to the radio program, also. A fun read - and quite
appropriate in today's world. :)

--
==================
Remove the "x" from my email address
Jerry Stuckle

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

OK, let's discuss dipoles vs length
 

On 10/12/2014 4:29 PM, wrote:
Ralph Mowery wrote:

"Ian Jackson" wrote in message
...
In message ,
writes
Like I said, there is no difference in free space between a V and an
inverted V.

There are slight differences when close to ground.

Assuming it's a halfwave dipole, I would have thought it was better to
concentrate on getting the centre (where the current is) as high as
possible, rather than the ends. [Obviously this depends on whether you
have a suitable sky-hook available for and at the centre.] However, I
believe that there is at least one commercial loaded dipole (essentially
for portable use, I think) that has a short mast, and the ends of the V
are up in the air.



In free space I would not think there would be much of any differance.

Near the ground where most of us are is what we have to live with. In my
back yard I have enough room to string wire dipoles for 80 meters and
shorter. I don't have a way to support the antennas in the middle. I can
go up about 60 feet or so at the ends.

60 feet is good for 30M, marginal for 40M, and crap for 80M and below
for a dipole.


I'll argue with that. I got WAS on 75 meters with an inverted vee with
an apex of 50'. I was in Iowa at the time - but had a pretty good
signal across the continental U.S. late at night.

There are many things to consider, and blanket statements like yours are
pretty much worth what people pay for them.

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

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

OK, let's discuss dipoles vs length
 

Jerry Stuckle wrote:
On 10/12/2014 2:59 PM, Lostgallifreyan wrote:
John S wrote in :

I know of Hitch-Hiker's Guide To The Galaxy, but I have never watched.
Probably my loss.

Not really. :) It's much better read, or maybe best of all, heard in the
original programs that went out on Radio 4 in the early evenings in the late
70's. Those are famous, likely easily had in various ways. I've seen the
movie, but it doesn't work for me so well. Some of it is great, but they
totally failed to get Marvin right, and that means they lost a lot of the
depth of it. I liked their Vogons though.


I prefer the book to the radio program, also. A fun read - and quite
appropriate in today's world. :)

I have the radio shows on tape in the car, very good for a long drive. Not
a patch on the book for me, though. I've read and re-read them loads of
times since I was a teenager. And the BBC TV series from the early 80s is
superior to the 2005 film in every way.

--
Stephen Thomas Cole // Sent from my iPhone

OK, let's discuss dipoles vs length
 

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

OK, let's discuss dipoles vs length
 

"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.

OK, let's discuss dipoles vs length
 

Jeff Liebermann wrote in
:

This might be useful:...

It it. :) I saved the whole post, to be sure I can find it fast any time. I
do have a habit of staying with one program so I'll be careful about that.
I'm already aware that NEC2 and NEC4 and MiniNEC all have things they are
particularly good at, so I'll not limit my choices the way I usually might.

OK, let's discuss dipoles vs length
 

I need to risk asking something that maybe should be obvious to me, just to
be sure I'm not starting on a very wrong assumption.. As I'm likely to only
be listening, when I see a Smith chart or other diagram indicating relative
signal transmission strength at some distance and direction, does this follow
the rule of many 'simple' transducers, in that the same chart exactly models
the sensitivity of the same antenna for reception? I'm hoping it does,
otherwise life might get complicated. :)

OK, let's discuss dipoles vs length
 

On 10/12/2014 2:14 PM, wrote:
John S wrote:
On 10/12/2014 1:21 PM, wrote:
John S wrote:
On 10/11/2014 12:51 PM, wrote:
John S wrote:

snip

OK, so lets analyze my results:

Conditions are free space, wire is #14 gauge but may have zero ohms
where noted. The antenna is a dipole with the source connected at the
center, F=7MHz. I'm using EZNEC with a source of 1 watt. Antenna
resonance plays no part in this. # segments = 99 unless otherwise noted.

Lambda Wire Rin Gavg(dbi) Gmax(dbi) Efficiency

0.5 zero 80 0 2.16 100%
0.5 #14 73.6 -.09 2.08 98%

0.25 zero 13.2 0 1.85 100%
0.25 #14 13.7 -.17 1.69 96%

0.125 zero 3 0 1.78 100%
0.125 #14 3.25 -.33 1.45 93%

0.05 zero .464 0 1.76 100%
0.05 #14 .556 -.78 0.98 83%

Rin is the terminal resistance only. Gave is the average gain integrated
over the pattern, Gmax is the highest gain detected.

Unless I have done something wrong, I see that a dipole that is .05
wavelengths long is within 20% of being as efficient as a half-wave
dipole. Even including wire resistance.

I invite discussion in any case.

The diameter of #14 solid wire is 0.0641"; how about a line for #8, which
is 0.1285"?


0.05 #8 0.515 -.41 1.36 91.1%


Free space, no ground loss.

So it seems that a .05 lamda dipole is only about 7% less efficient than
a full size dipole wit suitable wire...

So much for "short antennas are not efficient".

(snip extraneous input)


Yes, Jim, that is so. In fact, that was the hidden reason for the
exercise. I was hoping this would provide an example to let others know
that it is not the antenna length that is the problem as Gareth
proposed. I was hoping that others would take the investigation into
their own hands as a result.

I noted that you tried to foul me up with the unreasonable wire size.
EZNEC has a nice warning feature to take care of it.

What "unreasonable wire size"? #8 wire is readily available and often
used to make antenna elements, as is 1/8 th aluminum, which is only a
few thousands of an inch different.

Or are you refering to issues with segmentation and fat, short wires which I
thought I had warned you about?

Ok, wrong choice of words on my part. Sorry. Yes, I kinda thought you
were really testing me to see if I paid attention about the warning.

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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http://www.avast.com


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.

OK, let's discuss dipoles vs length
 

"Ralph Mowery" wrote in
:

The type of wire does not
matter, just the weight and how much tension you can put on it before it
breaks.

Well, the type of material kind of defines that. :) But I take your point.
Thanks for the extra detail.

OK, let's discuss dipoles vs length
 

Ian Jackson wrote:
In message ,
writes




60 feet is good for 30M, marginal for 40M, and crap for 80M and below
for a dipole.

It is also too high for 15M and up.

For best results, a diple should be at .5 labda.

Then again, a marginal 40M dipole is better than no antenna at all.

Regardless of the theory, in real life (with real-life ground
conductivity/reflectivity, and the prevalence of nearby clutter and
obstruction), I can't help feeling in my water that 'higher generally
works better'!!

Depends on what you mean by "higher".

As you start getting higher than 1/2 lambda, that one big lobe starts
becoming a lot of smaller lobes pointing into the sky.

Even the free demo version of EZNEC can show this.


--
Jim Pennino

OK, let's discuss dipoles vs length
 

On 10/13/2014 11:21 AM, Jeff Liebermann wrote:
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, maybe he is kind of asking about reciprocity in his own way?

OK, let's discuss dipoles vs length
 

Jerry Stuckle wrote:
On 10/12/2014 4:29 PM, wrote:
Ralph Mowery wrote:

"Ian Jackson" wrote in message
...
In message ,
writes
Like I said, there is no difference in free space between a V and an
inverted V.

There are slight differences when close to ground.

Assuming it's a halfwave dipole, I would have thought it was better to
concentrate on getting the centre (where the current is) as high as
possible, rather than the ends. [Obviously this depends on whether you
have a suitable sky-hook available for and at the centre.] However, I
believe that there is at least one commercial loaded dipole (essentially
for portable use, I think) that has a short mast, and the ends of the V
are up in the air.



In free space I would not think there would be much of any differance.

Near the ground where most of us are is what we have to live with. In my
back yard I have enough room to string wire dipoles for 80 meters and
shorter. I don't have a way to support the antennas in the middle. I can
go up about 60 feet or so at the ends.

60 feet is good for 30M, marginal for 40M, and crap for 80M and below
for a dipole.


I'll argue with that. I got WAS on 75 meters with an inverted vee with
an apex of 50'. I was in Iowa at the time - but had a pretty good
signal across the continental U.S. late at night.

There are many things to consider, and blanket statements like yours are
pretty much worth what people pay for them.

The only "blanket statements" in there is that 1/2 lambda is the OPTIMUM
height for an antenna. Above and below that height a good deal of the
patten goes to warming clouds.

Note the word "optimum"; that means that antennas at other heights do work,
just not as well as they could.

--
Jim Pennino

OK, let's discuss dipoles vs length
 

Jerry Stuckle wrote in news:m1gumv$73s$1@dont-
email.me:

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.


I doubt I could cope with that much risk of vertigo (occasionally I sufer the
real, medical thing, just waking up in the morning, but it's still rare enouh
that I prefer not to know more about why). I did see a video once though, I
saved it somewhere. Extremely interesting, as well as having a chance to see
so much of the climb in detail. I suspect you or someone here might even know
who made it.

OK, let's discuss dipoles vs length
 

Jerry Stuckle wrote in news:m1gvg0$9v8$1@dont-
email.me:

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.


Telewest, who became Blueyonder, then after merging with ATL got bought by
Vitgin Media here in Britain, used copper clad steel cores. I don't know
enough to comment on their reasons, but it's definitely true, I just waved a
magnet at a few cables of theirs to prove it. My guess is that because the
lines were ostensibly for cable TV, they just coerced them into internet
wiring later. ADSL on the phone lines later beat them for speed, presumably
because the phones were using solid copper, but I'm not sure they used in the
external cables because I can't reach one right now.

OK, let's discuss dipoles vs length
 

Jeff Liebermann wrote in
:

you might be referring to an antenna
pattern polar graph

That's the one. :) I'm too new to them to name them right, is all.

OK, let's discuss dipoles vs length
 

Jeff Liebermann wrote in
:

Antennas do not produce,
amplify, or "strengthen" RF. The only re-direct it.


Point taken, and I agree because they're passive constructions in metal. Even
before reading more, I'll have one quick retry..

If any given directional antenna can radiate at its best to one particular
direction, is it safe to assume that it will be at its best similarly aimed
when receiving?

OK, let's discuss dipoles vs length
 

In message ,
Lostgallifreyan writes
Jerry Stuckle wrote in news:m1gvg0$9v8$1@dont-
email.me:

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.


Telewest, who became Blueyonder, then after merging with ATL got bought by
Vitgin Media here in Britain, used copper clad steel cores. I don't know
enough to comment on their reasons, but it's definitely true, I just waved a
magnet at a few cables of theirs to prove it. My guess is that because the
lines were ostensibly for cable TV, they just coerced them into internet
wiring later. ADSL on the phone lines later beat them for speed, presumably
because the phones were using solid copper, but I'm not sure they used in the
external cables because I can't reach one right now.

Are you confusing the internet being carried (like cable TV) over coax
at RF, and via ADSL on twisted-pair phone lines? The coax drop cables
are usually RG6, which has a copper-plated steel inner.

If it's anything like some coax I worked with in the 60s, there might be
a small 'kink' in the frequency response* at around 40MHz, which is
probably the frequency at which all the RF has moved out of the steel
core, and into the copper plating.
*Above 40MHz, the attenuation might become somewhat lower than you would
expect from extrapolating loss figures obtained below 40MHz. While I
have to say that I've never noticed this with RG6, this may be because
I've never looked for it. In any case, it often has been in the
guardband where the crossover between the cable TV forward and reverse
RF paths occur.
--
Ian

OK, let's discuss dipoles vs length
 

On 10/13/2014 1:06 PM, Lostgallifreyan wrote:
Jerry Stuckle wrote in news:m1gumv$73s$1@dont-
email.me:

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.


I doubt I could cope with that much risk of vertigo (occasionally I sufer the
real, medical thing, just waking up in the morning, but it's still rare enouh
that I prefer not to know more about why). I did see a video once though, I
saved it somewhere. Extremely interesting, as well as having a chance to see
so much of the climb in detail. I suspect you or someone here might even know
who made it.


It was not I, and almost assuredly no on I know. The ones I knew back
then got out of the business - one way or the other.

I did see a video about a couple of guys free climbing an television
antenna about 2K feet in the air. I lost count how many safety
practices they violated. If OSHA had seen them doing that, they would
have been grounded big time. The fines would have probably put the
company out of business.

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

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

OK, let's discuss dipoles vs length
 

On 10/13/2014 2:23 PM, Ian Jackson wrote:
In message ,
Lostgallifreyan writes
Jerry Stuckle wrote in news:m1gvg0$9v8$1@dont-
email.me:

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.


Telewest, who became Blueyonder, then after merging with ATL got
bought by
Vitgin Media here in Britain, used copper clad steel cores. I don't know
enough to comment on their reasons, but it's definitely true, I just
waved a
magnet at a few cables of theirs to prove it. My guess is that because
the
lines were ostensibly for cable TV, they just coerced them into internet
wiring later. ADSL on the phone lines later beat them for speed,
presumably
because the phones were using solid copper, but I'm not sure they used
in the
external cables because I can't reach one right now.

Are you confusing the internet being carried (like cable TV) over coax
at RF, and via ADSL on twisted-pair phone lines? The coax drop cables
are usually RG6, which has a copper-plated steel inner.


The cheaper RG6 has copper clad steel. The stuff we use is
quad-shielded with a solid copper core.

If it's anything like some coax I worked with in the 60s, there might be
a small 'kink' in the frequency response* at around 40MHz, which is
probably the frequency at which all the RF has moved out of the steel
core, and into the copper plating.
*Above 40MHz, the attenuation might become somewhat lower than you would
expect from extrapolating loss figures obtained below 40MHz. While I
have to say that I've never noticed this with RG6, this may be because
I've never looked for it. In any case, it often has been in the
guardband where the crossover between the cable TV forward and reverse
RF paths occur.

I never tested it, but I think the skin effect would move the rf out of
the core at a lower frequency. Perhaps some ferromagnetic effect with
the steel?

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

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

OK, let's discuss dipoles vs length
 

On 10/13/2014 1:05 PM, wrote:
Jerry Stuckle wrote:
On 10/12/2014 4:29 PM, wrote:
Ralph Mowery wrote:

"Ian Jackson" wrote in message
...
In message ,
writes
Like I said, there is no difference in free space between a V and an
inverted V.

There are slight differences when close to ground.

Assuming it's a halfwave dipole, I would have thought it was better to
concentrate on getting the centre (where the current is) as high as
possible, rather than the ends. [Obviously this depends on whether you
have a suitable sky-hook available for and at the centre.] However, I
believe that there is at least one commercial loaded dipole (essentially
for portable use, I think) that has a short mast, and the ends of the V
are up in the air.



In free space I would not think there would be much of any differance.

Near the ground where most of us are is what we have to live with. In my
back yard I have enough room to string wire dipoles for 80 meters and
shorter. I don't have a way to support the antennas in the middle. I can
go up about 60 feet or so at the ends.

60 feet is good for 30M, marginal for 40M, and crap for 80M and below
for a dipole.


I'll argue with that. I got WAS on 75 meters with an inverted vee with
an apex of 50'. I was in Iowa at the time - but had a pretty good
signal across the continental U.S. late at night.

There are many things to consider, and blanket statements like yours are
pretty much worth what people pay for them.

The only "blanket statements" in there is that 1/2 lambda is the OPTIMUM
height for an antenna. Above and below that height a good deal of the
patten goes to warming clouds.

Note the word "optimum"; that means that antennas at other heights do work,
just not as well as they could.


"60 feet is good for 30M, marginal for 40M, and crap for 80M and below
for a dipole."

I have proof that is not the case. If the antenna were not crap, how
could I work both Alaska and Hawaii on 75 meters with an inverted V
having an apex at only 50'?

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

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

OK, let's discuss dipoles vs length
 

Jerry Stuckle wrote:
On 10/13/2014 1:05 PM, wrote:
Jerry Stuckle wrote:
On 10/12/2014 4:29 PM, wrote:
Ralph Mowery wrote:

"Ian Jackson" wrote in message
...
In message ,
writes
Like I said, there is no difference in free space between a V and an
inverted V.

There are slight differences when close to ground.

Assuming it's a halfwave dipole, I would have thought it was better to
concentrate on getting the centre (where the current is) as high as
possible, rather than the ends. [Obviously this depends on whether you
have a suitable sky-hook available for and at the centre.] However, I
believe that there is at least one commercial loaded dipole (essentially
for portable use, I think) that has a short mast, and the ends of the V
are up in the air.



In free space I would not think there would be much of any differance.

Near the ground where most of us are is what we have to live with. In my
back yard I have enough room to string wire dipoles for 80 meters and
shorter. I don't have a way to support the antennas in the middle. I can
go up about 60 feet or so at the ends.

60 feet is good for 30M, marginal for 40M, and crap for 80M and below
for a dipole.


I'll argue with that. I got WAS on 75 meters with an inverted vee with
an apex of 50'. I was in Iowa at the time - but had a pretty good
signal across the continental U.S. late at night.

There are many things to consider, and blanket statements like yours are
pretty much worth what people pay for them.

The only "blanket statements" in there is that 1/2 lambda is the OPTIMUM
height for an antenna. Above and below that height a good deal of the
patten goes to warming clouds.

Note the word "optimum"; that means that antennas at other heights do work,
just not as well as they could.


"60 feet is good for 30M, marginal for 40M, and crap for 80M and below
for a dipole."

I have proof that is not the case. If the antenna were not crap, how
could I work both Alaska and Hawaii on 75 meters with an inverted V
having an apex at only 50'?

What part of "optimum" is it that you did not understand?

If your point is that you disagree with what I said about 60 feet,
run a NEC analysis for 60 feet versus 1/2 lambda for the bands mentioned
and show me the error of my ways.



--
Jim Pennino

OK, let's discuss dipoles vs length
 

On 10/13/2014 3:21 PM, wrote:
Jerry Stuckle wrote:
On 10/13/2014 1:05 PM, wrote:
Jerry Stuckle wrote:
On 10/12/2014 4:29 PM, wrote:
Ralph Mowery wrote:

"Ian Jackson" wrote in message
...
In message ,
writes
Like I said, there is no difference in free space between a V and an
inverted V.

There are slight differences when close to ground.

Assuming it's a halfwave dipole, I would have thought it was better to
concentrate on getting the centre (where the current is) as high as
possible, rather than the ends. [Obviously this depends on whether you
have a suitable sky-hook available for and at the centre.] However, I
believe that there is at least one commercial loaded dipole (essentially
for portable use, I think) that has a short mast, and the ends of the V
are up in the air.



In free space I would not think there would be much of any differance.

Near the ground where most of us are is what we have to live with. In my
back yard I have enough room to string wire dipoles for 80 meters and
shorter. I don't have a way to support the antennas in the middle. I can
go up about 60 feet or so at the ends.

60 feet is good for 30M, marginal for 40M, and crap for 80M and below
for a dipole.


I'll argue with that. I got WAS on 75 meters with an inverted vee with
an apex of 50'. I was in Iowa at the time - but had a pretty good
signal across the continental U.S. late at night.

There are many things to consider, and blanket statements like yours are
pretty much worth what people pay for them.

The only "blanket statements" in there is that 1/2 lambda is the OPTIMUM
height for an antenna. Above and below that height a good deal of the
patten goes to warming clouds.

Note the word "optimum"; that means that antennas at other heights do work,
just not as well as they could.


"60 feet is good for 30M, marginal for 40M, and crap for 80M and below
for a dipole."

I have proof that is not the case. If the antenna were not crap, how
could I work both Alaska and Hawaii on 75 meters with an inverted V
having an apex at only 50'?

What part of "optimum" is it that you did not understand?

If your point is that you disagree with what I said about 60 feet,
run a NEC analysis for 60 feet versus 1/2 lambda for the bands mentioned
and show me the error of my ways.




You didn't say "optimum". You said it was "crap". What part of "crap"
don't you understand?

You think an NEC analysis is the slickest thing since snot on a
doorknob. But what about HAAT or ground conductivity, for instance?
You have considered neither when telling me my antenna was "crap" -
which it provably was not.

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

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

OK, let's discuss dipoles vs length
 

In message , Jerry Stuckle
writes
On 10/13/2014 2:23 PM, Ian Jackson wrote:
In message ,
Lostgallifreyan writes
Jerry Stuckle wrote in news:m1gvg0$9v8$1@dont-
email.me:

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.


Telewest, who became Blueyonder, then after merging with ATL got
bought by
Vitgin Media here in Britain, used copper clad steel cores. I don't know
enough to comment on their reasons, but it's definitely true, I just
waved a
magnet at a few cables of theirs to prove it. My guess is that because
the
lines were ostensibly for cable TV, they just coerced them into internet
wiring later. ADSL on the phone lines later beat them for speed,
presumably
because the phones were using solid copper, but I'm not sure they used
in the
external cables because I can't reach one right now.

Are you confusing the internet being carried (like cable TV) over coax
at RF, and via ADSL on twisted-pair phone lines? The coax drop cables
are usually RG6, which has a copper-plated steel inner.


The cheaper RG6 has copper clad steel. The stuff we use is
quad-shielded with a solid copper core.

As a copper-plated steel core has relatively high DC and low-frequency
resistance, solid copper core is usual anything carrying power (eg the
LNBs of satellite dishes). Tap-to-subscriber drop cable doesn't carry
power, and the cheaper steel/copper works just as well.

http://tinyurl.com/o89gfa8

If it's anything like some coax I worked with in the 60s, there might be
a small 'kink' in the frequency response* at around 40MHz, which is
probably the frequency at which all the RF has moved out of the steel
core, and into the copper plating.
*Above 40MHz, the attenuation might become somewhat lower than you would
expect from extrapolating loss figures obtained below 40MHz. While I
have to say that I've never noticed this with RG6, this may be because
I've never looked for it. In any case, it often has been in the
guardband where the crossover between the cable TV forward and reverse
RF paths occur.

I never tested it, but I think the skin effect would move the rf out of
the core at a lower frequency. Perhaps some ferromagnetic effect with
the steel?

I'm trying to remember what my kinky cable was. It might have been RG59.
I also think that the skin effect can produce some slightly odd effects
with stranded copper inner. However, it's got to be fairly long for you
to notice.


--
Ian

OK, let's discuss dipoles vs length
 

Jerry Stuckle wrote:

snip

You didn't say "optimum". You said it was "crap". What part of "crap"
don't you understand?

I will not engage in a ****ing contest with you.

You think an NEC analysis is the slickest thing since snot on a
doorknob. But what about HAAT or ground conductivity, for instance?

What about it?

Feel free to include all the above in your analysis.

You have considered neither when telling me my antenna was "crap" -
which it provably was not.

Where is the data that proves that?


--
Jim Pennino

OK, let's discuss dipoles vs length
 

On Mon, 13 Oct 2014 12:26:23 -0500, Lostgallifreyan
wrote:

If any given directional antenna can radiate at its best to one particular
direction, is it safe to assume that it will be at its best similarly aimed
when receiving?

Yes. For purposes of calculations and under most conditions, the
pattern is the same for transmit and receive for most antennas.

However, there are plenty of confusing exceptions. A common exception
is putting a 2.4GHz USB Wi-Fi dongle at the focus of a dish or corner
reflector. The USB dongle is almost an isotropic radiator, which
spews RF in all directions. If you transmit from the USB dongle, most
of the RF will never hit the dish antenna and wander off to parts
unknown. Only the part that hits the dish eventually ends up going
towards the other end of the wireless link. However, in receive,
almost all of the signal that hits the dish, gets reflected to the USB
dongle. Therefore the gain is higher in receive, than in transmit.

If the USB dongle were replaced with a proper dish feed, where the
bulk of the transmit RF hits the dish, the dish becomes more
"efficient". About 50% to 70% efficiencies are typical. However, it
is also possible to mess that up in the opposite direction. Instead
of a very non-directional feed, suppose I use as a feed, a high gain
directional antenna with a very narrow beamwidth. Instead of spraying
RF outside of the dish edge (over-spray), It puts all of it into a
narrow diameter spot somewhere on the dish surface. This time, the
symmetry is in the opposite direction. Transmit is fine, because all
of the power produced by the feed hits the spot and is radiated in the
direction of the other end of the link. However, receive is now a
problem because none of the RF seen by the dish OUTSIDE the area of
the spot is "seen" by the spot. Therefore, the gain is higher in
transmit, than in receive.

Gone to move some firewood...

--
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
 

"Jerry Stuckle" wrote in message
...
On 10/13/2014 1:06 PM, Lostgallifreyan wrote:
I did see a video about a couple of guys free climbing an television
antenna about 2K feet in the air. I lost count how many safety
practices they violated. If OSHA had seen them doing that, they would
have been grounded big time. The fines would have probably put the
company out of business.


I saw that video also. Don't think I would have been up there like that.

Saw another with a man and woman on the tower all dressed up for a formal
diner and singing a song.

Most I have climbed was 100 ft of Rohn 25. I did climb some silos at work
that were about 130 feet up. Just a ladder up the side, but they did have a
stepoff offset platform about every 30 feet.



---
This email is free from viruses and malware because avast! Antivirus protection is active.
http://www.avast.com

OK, let's discuss dipoles vs length
 

Jerry Stuckle wrote in news:m1h7sm$9bc$1@dont-
email.me:

I did see a video about a couple of guys free climbing an television
antenna about 2K feet in the air. I lost count how many safety
practices they violated. If OSHA had seen them doing that, they would
have been grounded big time. The fines would have probably put the
company out of business.


I can't find it to check, but I do remember it being very up-front about who
and where they were, and it was connected to soem company. The one I had was
probably kosher enough, if was effectively a promotional video, because
other, as you say, the effect would have been dramatically unwanted for them.
I could be wrong, but I won't know till I find it, and I have no idea where I
stowed it yet..

OK, let's discuss dipoles vs length
 

"Ralph Mowery" wrote in
:

Saw another with a man and woman on the tower all dressed up for a formal
diner and singing a song.


Whatever I saw, it wasn't that. Ò^O :)