Measuring Antenna Efficiency
 

Owen Duffy wrote:
Firstly you seem to assume that your 36 samples around the azimut circle
adequately fulfill Roy's "sampling the field at many points in all
directions", surely he mean't all elevation angles as well as all azimuth
angles.

What is the hourly rental charge on a helicopter? :-)
--
73, Cecil http://www.w5dxp.com

Measuring Antenna Efficiency
 

Cecil Moore wrote:
Owen Duffy wrote:

Firstly you seem to assume that your 36 samples around the azimut
circle adequately fulfill Roy's "sampling the field at many points in
all directions", surely he mean't all elevation angles as well as all
azimuth angles.


What is the hourly rental charge on a helicopter? :-)

that's what balloons and blimps are for, or model airplanes..

Measuring Antenna Efficiency
 

Owen wrote:
"Is that true?"

Only for limited conditions. Owen is correct that enough samples must be
taken to catch all variations in signal strength, in elevation and
azimuth if total radiated power is to be determined.

A simple vertical antenna rests on the earth and has a null at its tip.
It is far from an isotropic radiator.

The sampling I described is done on AM broadcast antennas. Only the wave
which travels along the earth is usually of any interest. The minimum
distance from the broadcast antenna for any field strength measurements
is usually one mile to be sure the far field is being measured.

The FCC`s ground wave intensity charts assume that if you have ground
conductivity such as sea water, a certain power and antenna efficiency
deliver 100 millivolts per meter at a distance of one mile from the
antenna. Field intensity in millivolts declines linearly with distance
so that at 10 miles you might have 10 mv/m if you have 100 mv/m at one
mile.Power is proportional to the square of the voltage.

Best regards, Richard Harrison, KB5WZI

Measuring Antenna Efficiency
 

Richard Harrison wrote:

The FCC`s ground wave intensity charts assume that if you have ground
conductivity such as sea water, a certain power and antenna efficiency
deliver 100 millivolts per meter at a distance of one mile from the
antenna. Field intensity in millivolts declines linearly with distance
so that at 10 miles you might have 10 mv/m if you have 100 mv/m at one
mile. . . .

The attenuation of the ground wave is the same as the free space
attenuation?

Roy Lewallen, W7EL

Measuring Antenna Efficiency
 

Roy Lewallen, W7EL wrote:
"The attenuation of the ground wave is the same as the free space
attenuation?"

No, it is greater. The attenuation of the ground wave is more rapid
because the soil has resistance and imposes a loss on the passing wave.

In free space, there is no ground loss and the signal loss is from the
spreading of the signal which reduces its density. It declines 6 dB (its
power is quartered) every time the distance from the transmitter
doubles, that is its volts per meter or signal strength is cut in half.

Ground waves decrease more rapidly with distance from the transmitter
due to imperfect conductivity in the earth`s surface. Loss goes up with
the operating frequency and with higher resistivity in the soil.

The FCC`s ground-wave field intensity charts cover limited frequency
ranges and each curve is for a specific soil conductivity.

Best regards, Richard Harrison, KB5WZI

Measuring Antenna Efficiency
 

Richard Harrison wrote:
Roy Lewallen, W7EL wrote:
"The attenuation of the ground wave is the same as the free space
attenuation?"

No, it is greater. The attenuation of the ground wave is more rapid
because the soil has resistance and imposes a loss on the passing wave.
. . .

I should hope so. That's why your statement that the field strength
decreases as the inverse of the distance in the context of AM broadcast
measurements at ground level was puzzling.

Roy Lewallen, W7EL

Measuring Antenna Efficiency
 

On Mon, 23 Apr 2007 17:30:20 -0700, Roy Lewallen
wrote:

Richard Harrison wrote:
Roy Lewallen, W7EL wrote:
"The attenuation of the ground wave is the same as the free space
attenuation?"

No, it is greater. The attenuation of the ground wave is more rapid
because the soil has resistance and imposes a loss on the passing wave.
. . .

I should hope so. That's why your statement that the field strength
decreases as the inverse of the distance in the context of AM broadcast
measurements at ground level was puzzling.

Richard had been reciting decade-for-decade declines of FS faithfully
from the FCC charts -over seawater- which he had specifically called
out.

"Faithfully" except for an inadvertent substitution of decade miles
for decade kilometers distance.

73's
Richard Clark, KB7QHC

Measuring Antenna Efficiency
 

Richard Clark, KB7QHC wrote:
"Faithfully" except for an inadvertent substitution of decade miles for
decade kilometers distance."

Thank you Richard for such a kind word as "inadvertent".

I make mistakes and I apologize for them. Hopefully, none of consequence
go uncorrected and mislead anyone. I learn more from my mistakes than
from correct postings but it isn`t my favorite way to learn. Thank you
to everyone who prompts me to search for the answer to an interesting
question.

I`m still puzzled about "cluster antennas".

Best regards, Richard Harrison, KB5WZI

Measuring Antenna Efficiency
 

On Tue, 24 Apr 2007 11:42:47 -0500, (Richard
Harrison) wrote:

I make mistakes and I apologize for them. Hopefully, none of consequence
go uncorrected and mislead anyone.

Hi Richard,

The simple mistake was of no consequence to the underlying
basis of your statement. As for misleading, your posts are too short
to develop convoluted imaginings posing as fact.

73's
Richard Clark, KB7QHC

Measuring Antenna Efficiency
 

I`m still puzzled about "cluster antennas".

Best regards, Richard Harrison, KB5WZI

I really don't know why it puzzles you. I have determined that
coupling of elements which means parasitic coupling is wastfull. To
avoid this coupling one must have elements that are all resonant. This
means ofcourse that element dimensions are necessarily different from
neighboring elements so that coupling per se ( there is no attraction
or repeling actions between elements) removed which thus creates an
arrangement that is in equilibrium. When elements are associated with
each other one can call them a 'collection' of elements or a 'cluster'
of elements. Now with respect to efficiency this array does not have
coupling associated with reflectors and directors thus if the array
was energised then a far field of radiation is formed without any
wastefull interaction of particles between elements. So when the far
field is formed the only "waste" of energy is that created by skin
resistance which is easily calculated, since without interaction
between elements non radiating energy collision losses cannot occur.
If one is looking for efficiency one usually work with input energy
equals output energy plus losses. When one is examining the amount of
radiation formed in the far field because one does not want to get
into a situation of interactive bombardment of partcles that do not
contribut to radiation in the far field prior to the generation of
radiation. This analysis I suppose can be considered a simple
relationship with Poyntings vector and in a way provides support for
Poynting where none existed before but I may be over reaching there in
some eyes. Hope that satisfies your curiousity
Art