"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

"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

"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

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

I should elaborate a little.

The average gain is the ratio of the total power in all directions at a
great distance (beyond the point where the surface wave has decayed to a
negligible value) to the power into the antenna from all the sources.
(There's a factor of two also involved when using a ground plane with
NEC but not with EZNEC.) So the average gain is the efficiency if you
consider ground reflection and the decay of the surface wave to be part
of the loss.

Roy Lewallen, W7EL

Roy Lewallen wrote:
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

On 5 Mar, 20:41, Roy Lewallen wrote:
I should elaborate a little.

The average gain is the ratio of the total power in all directions at a
great distance (beyond the point where the surface wave has decayed to a
negligible value) to the power into the antenna from all the sources.
(There's a factor of two also involved when using a ground plane with
NEC but not with EZNEC.) So the average gain is the efficiency if you
consider ground reflection and the decay of the surface wave to be part
of the loss.

Roy Lewallen, W7EL

Lets have another look at this.

Roy inferred that the radiation field volume is the total useful
output

He then goes on to say that average gain what ever that means relative
to the final radiation field is the efficiency.
He also adds a condition relative to the definition of efficiency that
this is only true IF you count ground reflection and the decay of the
surface wave to be part of the loss


Hmmm I don't think anybody would deny that surface wave represents a
loss
relative to usefull work though some might say it contributes to
current flow, but why single out ground reflection as a loss since
that can be useful?
So Roy is classifying efficiency as something he considers usefull
and ground reflection is not usefull. He also throws average gain into
the equation without providing a definition of average
gain ( like gain is an advance over something he doesn't want to
state)
Jimminy cricket
I agree that you need to provide more elaboration

Why is it you can't say the useful result of what you provided is the
radiation volume where efficiency is useful output over input times
100?
Why does one have to place conditions on :

efficiency = useful output/ actual input x 100 ?

Seems like efficiency in radiation is not the same as efficiencies
in other sciences. Possibly a definition supplied by a related
commitee
solely for their own interpretation even though it is not in
accordance with other diciplines. Also possibly based on the number of
books on a particular shelf.And then the following week they placed
conditions to clarify what efficiency includes and does not include
such as certain portions of radiation, possibly with a different color
to the norm
phew




Roy Lewallen wrote:
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- Hide quoted text -

- Show quoted text -

"art" wrote in message
oups.com...
On 5 Mar, 20:41, Roy Lewallen wrote:
I should elaborate a little.

The average gain is the ratio of the total power in all directions at a
great distance (beyond the point where the surface wave has decayed to a
negligible value) to the power into the antenna from all the sources.
(There's a factor of two also involved when using a ground plane with
NEC but not with EZNEC.) So the average gain is the efficiency if you
consider ground reflection and the decay of the surface wave to be part
of the loss.

Roy Lewallen, W7EL

Lets have another look at this.

Roy inferred that the radiation field volume is the total useful
output

He then goes on to say that average gain what ever that means relative
to the final radiation field is the efficiency.
He also adds a condition relative to the definition of efficiency that
this is only true IF you count ground reflection and the decay of the
surface wave to be part of the loss


Hmmm I don't think anybody would deny that surface wave represents a
loss
relative to usefull work though some might say it contributes to
current flow, but why single out ground reflection as a loss since
that can be useful?
So Roy is classifying efficiency as something he considers usefull
and ground reflection is not usefull. He also throws average gain into
the equation without providing a definition of average
gain ( like gain is an advance over something he doesn't want to
state)
Jimminy cricket
I agree that you need to provide more elaboration

Why is it you can't say the useful result of what you provided is the
radiation volume where efficiency is useful output over input times
100?
Why does one have to place conditions on :

efficiency = useful output/ actual input x 100 ?

Seems like efficiency in radiation is not the same as efficiencies
in other sciences. Possibly a definition supplied by a related
commitee
solely for their own interpretation even though it is not in
accordance with other diciplines. Also possibly based on the number of
books on a particular shelf.And then the following week they placed
conditions to clarify what efficiency includes and does not include
such as certain portions of radiation, possibly with a different color
to the norm
phew

"Ground reflection loss" is probably a more precise term.

Frank

"Roy Lewallen" wrote in message
...
I should elaborate a little.

The average gain is the ratio of the total power in all directions at a
great distance (beyond the point where the surface wave has decayed to a
negligible value) to the power into the antenna from all the sources.
(There's a factor of two also involved when using a ground plane with NEC
but not with EZNEC.) So the average gain is the efficiency if you consider
ground reflection and the decay of the surface wave to be part of the
loss.

Roy Lewallen, W7EL

I was using average gain for my calculation of efficiency; i.e.
XNDA = 1001, or 1002. I have also been considering
the factor of "2" in the results. To be accurate, and to
determine the radiation resistance of a structure, you do
need to include the surface wave. The only way I
can think of doing this is to sum "E X H" close enough
to the radiating structure so as to include all its
elements. At the moment I am using Excel
to compute the Poynting vector.
Even then, there is some question as
to how much ground absorption effects the results
between antenna and the hemispherical radius
of computation. I have noticed some weird results
if you get too close to the ends of a buried radial system.

Regards,

Frank (VE6CB)

"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.