Measuring Antenna Efficiency
 

On 5 Mar, 12:58, Owen Duffy wrote:
"Wayne" wrote innews:5cXGh.391$iD4.256@trnddc06:

When the subject of antenna efficiency comes up, it often involves a
discussion of ground losses on verticals. What about, for example, a

The reason for focus on ground loss on (HF) verticals is that, unless you
have taken extreme measures with a ground system, ground loss dwarfs
other losses and in that case dominates considerations of efficiency.
Next would come loading coils.

dipole? Could one calculate "power out/power in" by measuring the

Half wave dipoles made from practical materials are usually very high
efficiency, losses commonly range in the area of 1% to ~3%. Loading coils
are a significant loss element in loaded dipoles. Some folk (eg ARRL)
have a mind that linear loading (folding the conductors back on
themselves) is lossless, but my analysis of the Cobra shows that is not
the case, seehttp://www.vk1od.net/cobra/index.htm. Even other lengths
of unloaded dipoles may be very efficient, but the feedpoint impedance
may drive huge losses on the feedline and so whilst the radiator is
efficient, the antenna system may be inefficient.

Components of an antenna system interact with each other in a complex
way, and it is important to analyse the entire antenna system (radiator,
earth, transmission line, balun, ATU etc) to obtain a correct
understanding of how the system works overall.

VSWR and declaring that everything not reflected was transmitted? It

Roy has already explained to you that you have some misconceptions about
VSWR, "forward power", and "reflected power".

There has been another raging discussion here about what happens to the
"reflected power", it isn't necessarily, and isn't usually lost (ie
dissipated as heat), but as I have stated above the feedpoint impedance
may drive huge losses on the feedline, it may also reduce the power
available from the transmitter and may reduce the transmitter efficiency.

would seem more accurate to actually measure power out and power in,
but that introduces inaccuracies by having to calibrate the setup.
Thoughts?

In terms of efficiency on the larger scale, a significant of power is
lost in the process of reflecting some rays from real ground.

Owen

Oh my !!!!!!

My dipole has a 1:1 swr. Neigbour next door puts a fence around his
lot.
My SWR goes to 3:1. No problem, swr has no connection to efficiency
somebody said so everything is O.K.
Except what is the definition of efficiency? Radiation resistance,
effective use of the radiation, cancellation of radiation?????
You better get that bit straightened out before you enlarge and
expouse
other statements which may cancel the legitamacy of your response.
Another point to ponder on the other side. At what point can we
separate the formation of radiation, at the radiation surface, the
beginning of the near field the exit from the near field? If you are
going to talk efficiency
then you must have a closed border around which equilibrium is
determined
which brings us back to Gauss. Pretty neat!!
Art
Art

Measuring Antenna Efficiency
 

art wrote:

. . .

Except what is the definition of efficiency? Radiation resistance,
effective use of the radiation, cancellation of radiation?????

The definition of efficiency with respect to antennas is very well
defined, understood, and agreed upon in all the amateur and professional
literature. Virtually every text and professional paper uses an
identical definition, and that is: the fraction of the power applied to
an antenna which is radiated. I know that Art often uses the term to
mean several other different things which I don't believe he's ever
clarified (at least not that I could understand), so some caution should
be used in making assumptions about its meaning when used in this newsgroup.

. . .

Roy Lewallen, W7EL

Measuring Antenna Efficiency
 

"Wayne" wrote in message
news:5cXGh.391$iD4.256@trnddc06...
When the subject of antenna efficiency comes up, it often involves a
discussion of ground losses on verticals. What about, for example, a
dipole? Could one calculate "power out/power in" by measuring the VSWR
and declaring that everything not reflected was transmitted? It would
seem more accurate to actually measure power out and power in, but that
introduces inaccuracies by having to calibrate the setup. Thoughts?

As an example consider a horizontal 75 m dipole, constructed of
#14 AWG copper, at various heights above an average ground.
The radiation efficiency, according to NEC, is shown below:

height 10 ft, efficiency 14%;
height 30 ft, efficiency 54%,
height 90 ft efficiency 82%

The above results do not include the ground wave, which
can be considered lost power. Ground absorption also increases
with proximity to the ground.

Regards,

Frank

Measuring Antenna Efficiency
 

"Frank" wrote in news:f71Hh.16901$lY6.7593
@edtnps90:


"Wayne" wrote in message
news:5cXGh.391$iD4.256@trnddc06...
When the subject of antenna efficiency comes up, it often involves a
discussion of ground losses on verticals. What about, for example, a
dipole? Could one calculate "power out/power in" by measuring the
VSWR
and declaring that everything not reflected was transmitted? It would
seem more accurate to actually measure power out and power in, but
that
introduces inaccuracies by having to calibrate the setup. Thoughts?

As an example consider a horizontal 75 m dipole, constructed of
#14 AWG copper, at various heights above an average ground.
The radiation efficiency, according to NEC, is shown below:

height 10 ft, efficiency 14%;
height 30 ft, efficiency 54%,
height 90 ft efficiency 82%

The above results do not include the ground wave, which
can be considered lost power. Ground absorption also increases
with proximity to the ground.

Frank,

What is the figure for free space? I suspect closer to 99%. If that is
the case, don't your figures include loss (or absorbption) in rays
reflected by the ground?

Owen

Measuring Antenna Efficiency
 

On 5 Mar, 14:47, Roy Lewallen wrote:
art wrote:

. . .

Except what is the definition of efficiency? Radiation resistance,
effective use of the radiation, cancellation of radiation?????

The definition of efficiency with respect to antennas is very well
defined, understood, and agreed upon in all the amateur and professional
literature. Virtually every text and professional paper uses an
identical definition, and that is: the fraction of the power applied to
an antenna which is radiated. I know that Art often uses the term to
mean several other different things which I don't believe he's ever
clarified (at least not that I could understand), so some caution should
be used in making assumptions about its meaning when used in this newsgroup.

. . .

Roy Lewallen, W7EL

Exactly, whose definition, whose limitations, by what authority?
The term efficiency is universal in its intent and is measered by the
terms imposed. You did not pose any limitations of any kind. The word
efficiency is not identified with potato's in one part of science and
carrots in another part of science. It has true meaning in all
sciences relative to the context that is used. The number of books you
have is not a deciding factor tho it probably had a hand in you
ASSUMPTIONS
Art

Measuring Antenna Efficiency
 

"Owen Duffy" wrote in message
...
"Frank" wrote in news:f71Hh.16901$lY6.7593
........
As an example consider a horizontal 75 m dipole, constructed of
#14 AWG copper, at various heights above an average ground.
The radiation efficiency, according to NEC, is shown below:

height 10 ft, efficiency 14%;
height 30 ft, efficiency 54%,
height 90 ft efficiency 82%

The above results do not include the ground wave, which
can be considered lost power. Ground absorption also increases
with proximity to the ground.

Frank,

What is the figure for free space? I suspect closer to 99%. If that is
the case, don't your figures include loss (or absorbption) in rays
reflected by the ground?

Owen

Correct Owen. NEC shows 97.3% for free space, and 100 %,
as expected, with perfect conductors. Certainly the loss does
include absorption of the reflected rays. As mentioned before, in
previous threads, it is very tedious to determine what percentage
of the "Loss" is due to ground wave radiation. One of these
days I will write the code necessary to compute the actual
TRP including ground wave.

Frank

Measuring Antenna Efficiency
 

Frank wrote:

Correct Owen. NEC shows 97.3% for free space, and 100 %,
as expected, with perfect conductors. Certainly the loss does
include absorption of the reflected rays. As mentioned before, in
previous threads, it is very tedious to determine what percentage
of the "Loss" is due to ground wave radiation. One of these
days I will write the code necessary to compute the actual
TRP including ground wave.

That capability is already built into NEC, as the average gain calculation.

Roy Lewallen, W7EL

Measuring Antenna Efficiency
 

"Roy Lewallen" wrote in message
...
Wayne wrote:

Thanks for the reply. My dipole example is intended to avoid
transmission line issues by not having one, and the elements are assumed
to be reasonably low loss. If I do some quick back-of-the-envelope
calculations, for a VSWR of 1.3:1, I get an efficiency of about 98.3%
(using the equation 1-gamma^2). Assuming a resistance of 1 ohm in the
dipole conductors the efficiency I calculate is about 98.6% (72/73).

Are there any other loss issues missing in this example.

There is no relationship between SWR and efficiency.

Roy Lewallen, W7EL

Agreed. For example, SWR into a dummy load. The equation given was just to
show the approximation I was trying to make for the dipole case.

Measuring Antenna Efficiency
 

"Frank" wrote in message
news:_c3Hh.16918$lY6.10683@edtnps90...

"Owen Duffy" wrote in message
...
"Frank" wrote in news:f71Hh.16901$lY6.7593
.......
As an example consider a horizontal 75 m dipole, constructed of
#14 AWG copper, at various heights above an average ground.
The radiation efficiency, according to NEC, is shown below:

height 10 ft, efficiency 14%;
height 30 ft, efficiency 54%,
height 90 ft efficiency 82%

The above results do not include the ground wave, which
can be considered lost power. Ground absorption also increases
with proximity to the ground.

Frank,

What is the figure for free space? I suspect closer to 99%. If that is
the case, don't your figures include loss (or absorbption) in rays
reflected by the ground?

Owen

Correct Owen. NEC shows 97.3% for free space, and 100 %,
as expected, with perfect conductors. Certainly the loss does
include absorption of the reflected rays. As mentioned before, in
previous threads, it is very tedious to determine what percentage
of the "Loss" is due to ground wave radiation. One of these
days I will write the code necessary to compute the actual
TRP including ground wave.

Frank


Interesting. Thanks Frank.

Measuring Antenna Efficiency
 

Wayne wrote:
"Roy Lewallen" wrote in message

There is no relationship between SWR and efficiency.

Roy Lewallen, W7EL

Agreed. For example, SWR into a dummy load. The equation given was just to
show the approximation I was trying to make for the dipole case.


I don't seem to be communicating well, but that's not unusual. It's a
shortcoming I have. So I'll try again.

There is not even an approximate relationship between SWR and
efficiency, so what you calculated was not an approximation of the
efficiency. It was simply a number which has no relationship whatsoever
to the efficiency. You could have used any equation you might dream up,
and the result would be as meaningless as the result you got.

Roy Lewallen, W7EL