Yagi efficiency
 

Does anyone know why the efficiency of the Stanford Big Dish (150 feet)
is only 35% on 1420MHz, compared to 55% on 150 and 400MHz?

http://www-star.stanford.edu/rsg/bigdish.php

--Zack Lau W1VT

More than likely, mesh in the reflector is too big and parabolic perfection
is poorer at the higher frequency

W4ZCB

Yagi efficiency
 

Harold E. Johnson wrote:
Does anyone know why the efficiency of the Stanford Big Dish (150 feet)
is only 35% on 1420MHz, compared to 55% on 150 and 400MHz?

http://www-star.stanford.edu/rsg/bigdish.php

--Zack Lau W1VT

More than likely, mesh in the reflector is too big and parabolic perfection
is poorer at the higher frequency

According to my interpretation of material written by Dick Knadle,
K2RIW published in the ARRL Antenna Book, a reflector error on the
order of 1 inch peak to peak results in a gain deterioration of 0.3 dB
on 1420MHz. I doubt the mesh adds more than another 0.2 dB of loss.
There is still another 1.5 dB of loss to account for the lower
efficiency. Could the dish be optimized for receiving, sacrificing
some gain for a better gain to temperature ratio?

Zack Lau W1VT

W4ZCB

Yagi efficiency
 

Harold E. Johnson wrote:
Does anyone know why the efficiency of the Stanford Big Dish (150 feet)
is only 35% on 1420MHz, compared to 55% on 150 and 400MHz?

http://www-star.stanford.edu/rsg/bigdish.php

--Zack Lau W1VT

More than likely, mesh in the reflector is too big and parabolic perfection
is poorer at the higher frequency

According to my interpretation of material written by Dick Knadle,
K2RIW published in the ARRL Antenna Book, a reflector error on the
order of 1 inch peak to peak results in a gain deterioration of 0.3 dB
on 1420MHz. I doubt the mesh adds more than another 0.2 dB of loss.
There is still another 1.5 dB of loss to account for the lower
efficiency. Could the dish be optimized for receiving, sacrificing
some gain for a better gain to temperature ratio?

Zack Lau W1VT

W4ZCB

Yagi efficiency
 

"Zack" wrote in message
ups.com...

Harold E. Johnson wrote:
Does anyone know why the efficiency of the Stanford Big Dish (150 feet)
is only 35% on 1420MHz, compared to 55% on 150 and 400MHz?

http://www-star.stanford.edu/rsg/bigdish.php

--Zack Lau W1VT

More than likely, mesh in the reflector is too big and parabolic
perfection
is poorer at the higher frequency

According to my interpretation of material written by Dick Knadle,
K2RIW published in the ARRL Antenna Book, a reflector error on the
order of 1 inch peak to peak results in a gain deterioration of 0.3 dB
on 1420MHz. I doubt the mesh adds more than another 0.2 dB of loss.
There is still another 1.5 dB of loss to account for the lower
efficiency. Could the dish be optimized for receiving, sacrificing
some gain for a better gain to temperature ratio?

Zack Lau W1VT

W4ZCB

Please be a bit more careful where you plan your responses Zack, I wasn't
the one that posed that question above.

I suppose that they could be under-illuminating the dish in order to
suppress the "hot" ground behind it. For a dish that size though, one inch
is awfully tight. Why don't you ask them?

W4ZCB

Yagi efficiency
 

Art Unwin wrote:
"When one looks at a radiating array pattern one can see that the yagi
is very inefficient."

Efficiency is output over input. Antennas can be made very efficient.
When radiation resistance is large in comparison with waste (ohmic loss
resistance), efficiency is high. Directivity is something else.

Often, Terman answers antenna questions simply. This is such an
occasion. Terman writes on page 907 of his 1955 edition of "Electronic
and Radio Engineering":
"The Yagi antenna of Fig. 23-39, and the corner reflector, represent
about the best that can be achieved with respect to edirective gain in a
compact array."

Pity the fool who argues with Terman or Kraus.

Best regards, Richard Harrison, KB5WZI

Yagi efficiency
 

"art" wrote in message
oups.com...
Dan,
you know quite well what the post that started this thread asked for.
I only added the TOA comments to fill in some body where I was
coming from not for advice on what antenna to build.
People are quibling over the word "efficiency" which I find rather
wierd
especially since I am supposed to be in the company of fellow
engineers.
The subject was antenna radiation patterns and ascertaining the
relative volume of the main lobe which is the reason for an antenna and
comparing it to the total volume of the array which one accepts to
obtain the desirable primary lobe. Oh yes, when we talk of efficiency
one must multiply the ratio by 100 Some may have forgotten that!
Obviously this group comprises of a swarm of tadpoles with a few little
goldfish in a small pond none of which are qualified to be termed
faculty. Now you have something to get your teeth into since you deign
to respond to the initial post This term "I don't understand" is
usually used by student who enter class after late night partying and
it didn't work then either. A dull brain is a dull brain unless one
activates it.
Carry on with a thread of your own choice and quibble amongst
yourselves about what "is" is really meant by use of the word "is" For
what was a very short question this thread has gone amok and is way to
long
Art

wrote:
The moral of inventing meanings for words is that those meanings have
a short shelf life. This kind of thing doesn't even last out a week
in the white house press room.

True, true. If only all this word-twisting energy could be harnessed
as valid antenna design... the chipster seems to have relegated himself
these days to fairly innocuous posts elsewhere regarding staying on the
good side of your neighbors' graces by putting up visually low profile
antennas... Certainly a change from the f-word antenna wars of old. I
was a regular reader of r.r.a.a. in those days... not much of a poster
back then, though.

I wonder if a thousand-mile long, five mile high stack of rhombics
might meet Art's requirements... of course, at that point you could
just run open wire line to any distant receiver. That would be quite
efficient, from Art's standpoint.

73,
Dan


Your definition of efficencency was accepted and then a very good answer
within the boundaries of your definition was given which you rejected. The
fact is if you could recover all the energy that goes into the sidelobes or
radiates from the rear of the antenna and place it in the main beam you
would increase power in that direction precious little. Apparently what you
are seeking is a LASER beam performing in the HF spectrum. Even this would
not be very "efficent" for communicating from one point on the surface of
the earth to another point below the horizon that is to say you cant send a
signal through the Earth. Communication through the air via radio is
inherently inefficent if you look at it from the standpoint of thousands to
millions of watts at the transmitter with only microwatts being received.
In the futre we may learn to transmit nearly all of the power to a distant
point. If this happenes the most efficent method of getting an HF signal
across the ocean will be a moot point. By then will will be doing
matter/energy/matter conversion so that we will be able to transmit
ourselves over long distances if this is at all possible. In the mean time
hams will continue to make do with a very inefficent medium even by todays
standards


It is true that in the past we have accepted many thing that were true which
was not, many of these errors have been corrected at what seems to be an
expotential rate over the past couple of hundred years. Much of this was
accomplished by people viewing the world with a degree of open-mindedness
that had never existed in the past and this is a very good thing. Being
totally opened minded has it fallicies in making us not being able to
recognize when we have the correct answer. My mother as I am sure a lot of
other mothers have said this best. "I am open minded, just not so much as to
let my brains fall out." It is our closed mindedness that keeps of from
running off accepting every BS explantion that comes along


It has been your choice to deem anything someone says to you that you do not
agree with as RUDENESS. Perhaps we should all be POLITE to you and let you
go ahead with your fools errand. I doubt if most of us could be that cruel.
Actually most people are very polite to you in the truest snese of the word
carefully trying to explain things to you that you clearly do not
understand, trying to explain to you a reality you refuse to accept.

Yagi efficiency
 

Harold E. Johnson wrote:

Please be a bit more careful where you plan your responses Zack, I wasn't
the one that posed that question above.

My apologies--I didn't mean to make it look like you asked that
question.

73--Zack Lau W1VT

Yagi efficiency
 

Zack wrote:
My apologies--I didn't mean to make it look like you asked that
question.

The newsreader nested attributions indicated that he did
not write the posting immediately following his name so
you didn't really mis-attribute anything.
--
73, Cecil, http://www.qsl.net/w5dxp

Yagi efficiency
 

"art" wrote in message
ups.com...

Dave wrote:
"art" wrote in message
ups.com...

Richard Clark wrote:
On 21 Sep 2006 19:09:38 -0700, "art" wrote:

Notwithstanding that the
upper half of the major lobe serves no usefull purpose to what the
antenna is required for there is a mass of radiation in many
directions
and levels that have no connection to the required purpose of the
antenna, thus we have a lot of wasted radiation that if we harness it
so that it is used for the antennas primary use the efficiency of the
antenna would increase immensly.

Hi Art,

The classic solution is to stack yagis vertically. This draws down
the higher radiation lobes and puts their gain in the forward
direction.

Well you are getting closer to the question at hand. You have now
doubled the
power input but only slightly gained directionality(2db) efficiency I
would also suspect that you have flattened the lower lobe only into a
pancake shape. But again I go back to the desirable radiation which can
be said in this case to be the lower half of the major lobes half power
envelope which for a directional radiated array is very small compared
to the total radiated field.True propagation can play games but the
ARRL
give the average arrival angles over a 11 year period so it is not a
hopeless task to get a ball park figure regarding usefull radiation
knowing where the target is
I suppose I could make a model and slice out the half power lobe
portion and compare the two volumes for myself, I just thought that it
had already been looked at
Oh well back to the drawing board
Art

what you are missing is the variability in that arrival angle. if you
are
interested in a specific path you must be able to receive all the
possible
arrival angles, which with yagi's requires mounting several of them at
different heights. for instance consider a path from w1 to western
europe
at the sunspot peak on 10m... it is not uncommon for the band to open at
a
very low angle, say where a single yagi at 120' is the best antenna, then
as
the day progresses the angle increases so much that the 120' antenna is
almost worthless but one at only 30' is working great. if you put
everything into getting that 10-12 degree angle you lose out by mid
morning
when the arrival angle is up to 30 degrees or more...


David that is not absolutely correct, we are talking about a single
point to point communication where the arrival angle is below 10
degrees. If the angle of arrival is above that then it is created by
unusual propagation or deflection of radiation path. For a given
distance one can say that the communication energy level is comensurate
with the number of skips taken where a point is reached when the number
of skips controls the amount of energy left at the communication
distance. Thus the east may hear the west coast talking to Europe where
they cannot hear the transmitting station because of the excessive
number of hops. Remember, I am talking about point to point
communication
which largely defined by the number of skips taken which is why dipole
to dipole transmissions are pushed aside for those desiring DX contacts
tho I am sure you are not advocating dipoles for DX.



but at the same time
that top antenna may be working great into siberia!

what you are looking for is not normally called 'efficiency', but
'directivity'. unfortunately horizontally polarized yagi's vertical
radiation pattern is very dependent on height

do you really mean "vertical: radiation pattern?

and the terrain so increasing
the directivity is seen mostly in the width of the pattern. and as noted
above, controlling the vertical pattern is normally done by changing the
antenna height, usually by stacking multiple antennas on the tower and
selecting them one at a time or in combinations to give the desired
vertical
coverage.

No... stacking is used purely to provide a vector to combat the earths
magnetic field
which affects all radiation directional patterns not only a vertical
pattern

There have been some experiments with variable phasing of stacked
yagis, but it is not a common capability in amateur installations.

Exactly since these methods provide a vectoir to counteract the
terrains magnetic field
unfortunately this requires extra power supply points where the desire
is for just one.
Art


you have some big misconceptions that i can't begin to address here.. but
just a couple of points for you to go study on.
1. the arrival angle is not a fixed value for a point to point circuit. the
angle changes with the height of the ionosphere and also with which layers
are supporting the path at the time. the angle can change minute by minute,
or it can be fairly constant for hours depending on the state of the
ionosphere. but it will not be constant for all time.

2. also, it is not like the pretty single ray that some people draw when
showing reflections off the ionosphere. the ionosphere is not a mirror, it
is a gradient in a layer of ionization. the signals that are 'reflected'
are actually refracted and do not arrive perfectly focused as they went up.
in addition the polarization is changed which affects the efficiency of the
path, this is very evident on 160m and 80m where the prefered polarization
can change hour by hour over night.

3. i have no idea where you are going with this idea of stacking is to
combat the earths magnetic field. the only effect the earths magnetic field
has is on the ionosphere, not on how your antenna works. it is well known
that changing the height of a yagi changes the vertical radiation pattern
and hence the arrival angles that it favors. stacking yagis at different
heights and selecting them separately or in combinations lets you adjust the
elevaion pattern to compensate for the changes in the arrival angle. in
most cases all the yagis in a stack are fed in phase so their signals
combine at the horizon, but there have been some experiments where the
phasing is changed to intentionally raise the pattern higher to cover
different arrival angles more efficiently.

Yagi efficiency
 

"art" wrote in message
oups.com...
Wow Yuri has arrived

I remember that long discusting arguement he had with Tom Rauch
that brought words to the fore that brought shame to amateur radio
I'm gone, I want no part of what is now on the near horizon
Have a great year fellars I enjoyed the short visit while it lasted
Art




You should rattle your head to get your memory straight.

Who brought "shame" to amateur radio? W8JI for claiming nonsense that
current along the antenna loading coil is constant and Art for patenting
Yagi Reflector being shorter than driven element, or those who objected to
fallacies being propagated on the waves of the RRAA?

Looks like your logic is a little "converted" or inverted or deflected.

Keep it up, you are way ahead of us :-)

73

Yagi efficiency
 

a yagi reflector CAN be shorter than the driven element, if the driven
element is longer than 1/2 wavelength... not common, but it is possible.


"Yuri, K3BU" wrote in message
...

"art" wrote in message
oups.com...
Wow Yuri has arrived

I remember that long discusting arguement he had with Tom Rauch
that brought words to the fore that brought shame to amateur radio
I'm gone, I want no part of what is now on the near horizon
Have a great year fellars I enjoyed the short visit while it lasted
Art




You should rattle your head to get your memory straight.

Who brought "shame" to amateur radio? W8JI for claiming nonsense that
current along the antenna loading coil is constant and Art for patenting
Yagi Reflector being shorter than driven element, or those who objected to
fallacies being propagated on the waves of the RRAA?

Looks like your logic is a little "converted" or inverted or deflected.

Keep it up, you are way ahead of us :-)

73

Yagi efficiency
 

Dave wrote:

a yagi reflector CAN be shorter than the driven element, if the driven
element is longer than 1/2 wavelength... not common, but it is possible.



We already know how much Yuri doesn't. ;)

tom

Yagi efficiency
 

Cecil, efficiency depends on what your objectives are
The yagi antennas objective is to obtain a radiation beam of gain
compared
to radiation else where. What is wanted is a radiation lobe that one
can use to direct communication. ..rThe yagi achieves the object of
producing a lobe which has a higher gain than other lobes that the yagi
produces.( A higher ratio) The yagi achieves its object by producing
this
main lobe but at what cost? If we look at pattern volume as reflecting
as energy applied to the yagi we must compare that volume with the
whole pattern volume. This means comparing the volume of the upper
lobes, the side lobes, the rear lobe and of course the vertical lobe to
the main lobe. Any cursury look at a three D radiation pattern will
immediately see that the main lobe is less than 50 % of the total
radiation pattern
Let us look at a common dipole with a reflector, the planar view of
radiation which ignores radiation outside the plane is a figure 8 where
the addition of a reflector does nothing to enhance increased forward
radiation so immidiately we can say that the forward lobe achieves what
is termed a major lobe plus other forward lobes outside of the main
lobe
where as the radiation to the rear achieves nothing that enhances the
forward main lobe. So just comparing the forward and the rear lobe we
have only achieved 50 per cent of our object
and this is not counting other losses. Now you may disagree with the
objective of a yagi beam and I understand that may be the case.
Hopefully the above answers your request to
define efficiency as I was with respect to the yagi antenna. I think
the above pretty much explains what I stated in the initial post tho it
appears that some read inbetween the lines to read what they wanted to
read as a diversionary tactic and there is not much anybody can do
about that. One really has to ask themselves the question that if an
antenna came on the market with only one main lobe would they buy it
Art.

Cecil Moore wrote:
art wrote:
When one looks at a.radiating array pattern one can see that the yagi
is very inefficient.

Please define "efficiency".
--
73, Cecil, http://www.w5dxp.com

Yagi efficiency
 

Cecil, efficiency depends on what your objectives are
The yagi antennas objective is to obtain a radiation beam of gain
compared
to radiation else where. What is wanted is a radiation lobe that one
can use to direct communication. ..rThe yagi achieves the object of
producing a lobe which has a higher gain than other lobes that the yagi
produces.( A higher ratio) The yagi achieves its object by producing
this
main lobe but at what cost? If we look at pattern volume as reflecting
as energy applied to the yagi we must compare that volume with the
whole pattern volume. This means comparing the volume of the upper
lobes, the side lobes, the rear lobe and of course the vertical lobe to
the main lobe. Any cursury look at a three D radiation pattern will
immediately see that the main lobe is less than 50 % of the total
radiation pattern
Let us look at a common dipole with a reflector, the planar view of
radiation which ignores radiation outside the plane is a figure 8 where
the addition of a reflector does nothing to enhance increased forward
radiation so immidiately we can say that the forward lobe achieves what
is termed a major lobe plus other forward lobes outside of the main
lobe
where as the radiation to the rear achieves nothing that enhances the
forward main lobe. So just comparing the forward and the rear lobe we
have only achieved 50 per cent of our object
and this is not counting other losses. Now you may disagree with the
objective of a yagi beam and I understand that may be the case.
Hopefully the above answers your request to
define efficiency as I was with respect to the yagi antenna. I think
the above pretty much explains what I stated in the initial post tho it
appears that some read inbetween the lines to read what they wanted to
read as a diversionary tactic and there is not much anybody can do
about that. One really has to ask themselves the question that if an
antenna came on the market with only one main lobe would they buy it
Art.

Cecil Moore wrote:
art wrote:
When one looks at a.radiating array pattern one can see that the yagi
is very inefficient.

Please define "efficiency".
--
73, Cecil, http://www.w5dxp.com

Yagi efficiency
 

art wrote:
. . .
Any cursury look at a three D radiation pattern will
immediately see that the main lobe is less than 50 % of the total
radiation pattern . . .

Out of curiosity, did you

a) not read
b) not understand, or
c) not believe

what I posted about the fraction of power in a Yagi's minor lobes?

A cursory look at a 3D pattern is probably one of the least reliable
ways to determine anything quantitative about an antenna pattern. By
choosing the scale (e.g., field strength, power density, linear dB,
ARRL-scale dB), you can make the relative sizes of the lobes just about
anything you'd like and lead the casual observer to the conclusion of
your choice(*). But why bother trying to divine a value from a 3D
pattern, when it's so simple to numerically show that the power in the
lobes is insignificant?

(*) One of the slides in the "Antenna Basics" talk I've given at many
hamfests shows several very different directional patterns, and I ask
the audience which one is the most desirable. After the votes are in, I
reveal that they're all the same antenna, just drawn to different common
and legitimate scales.

Roy Lewallen, W7EL

Yagi efficiency
 

Roy Lewallen wrote:
art wrote:
. . .
Any cursury look at a three D radiation pattern will
immediately see that the main lobe is less than 50 % of the total
radiation pattern . . .

Out of curiosity, did you

a) not read
b) not understand, or snip

I did not understand your logic.
Front to back means nothing in terms of energy containment
The measerment is a ratio not a quantity
It also is a ratio only for a given plane and does not account for
anything outside that plane.
Have I stated anything wrong there?

Point out the error of my ways starting with a simple dipole. Does any
additional element to the array revert the radiation from the rear
direction so that it is additive to the forward directive radiation of
the main lobe? If so what percentage of the rearward radiation in the
rear hemisphere,,(ot a planar amount) ? The question is to you Roy to
answer for a one on one,It would help if you gave an actual percentage
instead of a "major fraction" which you stated before

And if you don't understand then just drop the thread as it has gone
on way to long with relatively little specifics with respect to the
original post
Art








c) not believe

what I posted about the fraction of power in a Yagi's minor lobes?

A cursory look at a 3D pattern is probably one of the least reliable
ways to determine anything quantitative about an antenna pattern. By
choosing the scale (e.g., field strength, power density, linear dB,
ARRL-scale dB), you can make the relative sizes of the lobes just about
anything you'd like and lead the casual observer to the conclusion of
your choice(*). But why bother trying to divine a value from a 3D
pattern, when it's so simple to numerically show that the power in the
lobes is insignificant?



I do not remember seeing any numerical answer ,was it specific and
relative to the
contained energy in the primary lobe because that is what I was looking
for ?
What was the actual percentage that you arrived at?



(*) One of the slides in the "Antenna Basics" talk I've given at many

Roy
the actual scale doesn't matter one iota on a given pattern with
respect to my question !
To compare different patterns one must have a common denominator such
as scale,
to do otherwise is an attempt to deceive. You also use the word
"desirable"and my connoctation of that is a major lobe and nothing else
whereas some may look for other characteristics. Did the group come to
a consensus as to what was desirable? Some may want to hear what is
said behind their backs!


erns, and I ask
the audience which one is the most desirable. After the votes are in, I
reveal that they're all the same antenna, just drawn to different common
and legitimate scales.

Roy Lewallen, W7EL

Yagi efficiency
 

art wrote:

I did not understand your logic.
Front to back means nothing in terms of energy containment
The measerment is a ratio not a quantity
It also is a ratio only for a given plane and does not account for
anything outside that plane.
Have I stated anything wrong there?

I thought your interest was in the amount of power contained in lobes
other than the main lobe of a Yagi. My posting showed a simple way to
relate front to back ratio, which is commonly known for many Yagis, to
the fraction of power in secondary lobes, which is not.

Point out the error of my ways starting with a simple dipole. Does any
additional element to the array revert the radiation from the rear
direction so that it is additive to the forward directive radiation of
the main lobe?

Of course.

If so what percentage of the rearward radiation in the
rear hemisphere,,(ot a planar amount) ? The question is to you Roy to
answer for a one on one,It would help if you gave an actual percentage
instead of a "major fraction" which you stated before

In my earlier posting I apparently overestimated your ability to do what
I thought was a simple calculation. So I'll do it for you so you can
have a number.

Since there's no "typical" Yagi, I presented one which most people would
consider to be worse than average -- one having only a 6 dB front/back
ratio. I also assumed for a starting point that the shape of the rear
lobe (that is, beamwidth and height) is the same as the front lobe. The
first calculation is to determine just what the ratio is of the powers
in the front and rear lobe. The answer is 4:1. That is, the front lobe
contains four times the power of the rear lobe. Since you seem to be
interested in energy rather than power, simply consider the amount of
energy each radiates in some amount of time: each second or other unit
of time, the forward lobe radiates four times the energy of the rear lobe.

What this says is that if you manage to get all the reverse-lobe power
(or energy, if you prefer) into the front lobe, without any change in
the front lobe's shape, you'd increase the gain just about exactly 1 dB.
If you end up fattening it, you'll lose some or all of that gain.

So there are some numbers for you. You'll have to do a bit of estimating
if the rear lobe is fatter or skinnier than the front lobe, but now you
have a number to start from.

Or let's say that the front/back is 10 dB instead of 6, a more typical
number for a Yagi. With the same criterion of similar lobe shapes, the
power ratio for the front and rear lobes is 10:1. So if you got all that
rear lobe power or energy into the front lobe without changing its
shape, you'd gain a whopping 0.4 dB. If you had two equal rear lobes,
both 10 dB below the front lobe, and both of the same shape as the front
lobe, the power ratio of the front to all rear lobes would be 5:1, and
you'd be able to increase your forward gain by 0.8 dB if you got all
that rear power into the front lobe without changing its shape.

So there's your actual percentage -- around 25% for a very poor Yagi,
and around 10 - 20% for a fair-to-middlin' one. From which you could
gain about a dB by very hard work in getting all that rear lobe power
into the front lobe(*).

If you question any of the calculations, I'll be glad to show how I
converted ratios to dB and vice-versa, although you should be able to
find this in many publications, as well as on the web. Or you can
continue drawing your conclusions from cursory looks at 3D plots. Your
choice.

And if you don't understand then just drop the thread as it has gone
on way to long with relatively little specifics with respect to the
original post

I'm afraid I do understand, but it's a good idea anyway.

(*) Being an engineer, I didn't include placebo effect gain in the
calculations. After a lot of hard work squeezing every last bit of power
into that front lobe, the signals are going to *seem* a lot stronger,
and the reports sure to be better.

Roy Lewallen, W7EL

Yagi efficiency
 

art wrote:
Cecil, efficiency depends on what your objectives are ...

I guess that is why there are 20 definitions for "efficiency"
in the IEEE Dictionary. One needs to state one's definition
of "efficiency" at the beginning of the discussion to avoid
confusion with all the other possible definitions. For instance,
Power Company EEs have a different definition of "power" than
do physicists, politicians, and priests.
--
73, Cecil http://www.w5dxp.com

Yagi efficiency
 

Roy Lewallen wrote:
art wrote:

I did not understand your logic.
Front to back means nothing in terms of energy containment
The measerment is a ratio not a quantity
It also is a ratio only for a given plane and does not account for
anything outside that plane.
Have I stated anything wrong there?

I thought your interest was in the amount of power contained in lobes
other than the main lobe of a Yagi. My posting showed a simple way to
relate front to back ratio, which is commonly known for many Yagis, to
the fraction of power in secondary lobes, which is not.

Point out the error of my ways starting with a simple dipole. Does any
additional element to the array revert the radiation from the rear
direction so that it is additive to the forward directive radiation of
the main lobe?

Of course.

If so what percentage of the rearward radiation in the
rear hemisphere,,(ot a planar amount) ? The question is to you Roy to
answer for a one on one,It would help if you gave an actual percentage
instead of a "major fraction" which you stated before

In my earlier posting I apparently overestimated your ability to do what
I thought was a simple calculation. So I'll do it for you so you can
have a number.

Since there's no "typical" Yagi, I presented one which most people would
consider to be worse than average -- one having only a 6 dB front/back
ratio. I also assumed for a starting point that the shape of the rear
lobe (that is, beamwidth and height) is the same as the front lobe. The
first calculation is to determine just what the ratio is of the powers
in the front and rear lobe. The answer is 4:1. That is, the front lobe
contains four times the power of the rear lobe.

I am not interested in front to back for what I am looking for but this
4:1 has my interest
What does it represent and how did you get it? The rear usually has
more than one lobe
and the reflector ndestructs or deflects the energy to 90 degrees of
impact. But that 4:1
figure where does it come from?
Art






Since you seem to be
interested in energy rather than power, simply consider the amount of
energy each radiates in some amount of time: each second or other unit
of time, the forward lobe radiates four times the energy of the rear lobe.

What this says is that if you manage to get all the reverse-lobe power
(or energy, if you prefer) into the front lobe, without any change in
the front lobe's shape, you'd increase the gain just about exactly 1 dB.
If you end up fattening it, you'll lose some or all of that gain.

So there are some numbers for you. You'll have to do a bit of estimating
if the rear lobe is fatter or skinnier than the front lobe, but now you
have a number to start from.

Or let's say that the front/back is 10 dB instead of 6, a more typical
number for a Yagi. With the same criterion of similar lobe shapes, the
power ratio for the front and rear lobes is 10:1. So if you got all that
rear lobe power or energy into the front lobe without changing its
shape, you'd gain a whopping 0.4 dB. If you had two equal rear lobes,
both 10 dB below the front lobe, and both of the same shape as the front
lobe, the power ratio of the front to all rear lobes would be 5:1, and
you'd be able to increase your forward gain by 0.8 dB if you got all
that rear power into the front lobe without changing its shape.

So there's your actual percentage -- around 25% for a very poor Yagi,
and around 10 - 20% for a fair-to-middlin' one. From which you could
gain about a dB by very hard work in getting all that rear lobe power
into the front lobe(*).

If you question any of the calculations, I'll be glad to show how I
converted ratios to dB and vice-versa, although you should be able to
find this in many publications, as well as on the web. Or you can
continue drawing your conclusions from cursory looks at 3D plots. Your
choice.

And if you don't understand then just drop the thread as it has gone
on way to long with relatively little specifics with respect to the
original post

I'm afraid I do understand, but it's a good idea anyway.

(*) Being an engineer, I didn't include placebo effect gain in the
calculations. After a lot of hard work squeezing every last bit of power
into that front lobe, the signals are going to *seem* a lot stronger,
and the reports sure to be better.

Roy Lewallen, W7EL

Yagi efficiency
 

"art" wrote in message
oups.com...
Cecil, efficiency depends on what your objectives are
The yagi antennas objective is to obtain a radiation beam of gain
compared
to radiation else where. What is wanted is a radiation lobe that one
can use to direct communication. ..rThe yagi achieves the object of
producing a lobe which has a higher gain than other lobes that the yagi
produces.( A higher ratio) The yagi achieves its object by producing
this
main lobe but at what cost? If we look at pattern volume as reflecting
as energy applied to the yagi we must compare that volume with the
whole pattern volume. This means comparing the volume of the upper
lobes, the side lobes, the rear lobe and of course the vertical lobe to
the main lobe. Any cursury look at a three D radiation pattern will
immediately see that the main lobe is less than 50 % of the total
radiation pattern
Let us look at a common dipole with a reflector, the planar view of
radiation which ignores radiation outside the plane is a figure 8 where
the addition of a reflector does nothing to enhance increased forward
radiation so immidiately we can say that the forward lobe achieves what
is termed a major lobe plus other forward lobes outside of the main
lobe
where as the radiation to the rear achieves nothing that enhances the
forward main lobe. So just comparing the forward and the rear lobe we
have only achieved 50 per cent of our object
and this is not counting other losses. Now you may disagree with the
objective of a yagi beam and I understand that may be the case.
Hopefully the above answers your request to
define efficiency as I was with respect to the yagi antenna. I think
the above pretty much explains what I stated in the initial post tho it
appears that some read inbetween the lines to read what they wanted to
read as a diversionary tactic and there is not much anybody can do
about that. One really has to ask themselves the question that if an
antenna came on the market with only one main lobe would they buy it
Art.

Cecil Moore wrote:
art wrote:
When one looks at a.radiating array pattern one can see that the yagi
is very inefficient.

Please define "efficiency".
--
73, Cecil, http://www.w5dxp.com


There are already words defined to mean the antenna parameters you are
talking about. I suggest you use these instead of defining yur own so people
will know what you are talking about. Antenna patterns are expressed in db.
This means they are logarthmicly compressed. IF they were displayed linearly
the sidelobes would would be invisible on the graph. Again. ad nauseum,
there is no significant power in a sidelobe of any reasonably designed yagi
antenna..

Yagi efficiency
 

On 29 Sep 2006 05:47:14 -0700, "art" wrote:

one having only a 6 dB front/back ratio.

But that 4:1 figure where does it come from?

Hi Art,

Do you know how to work a calculator using logarithms?

73's
Richard Clark, KB7QHC

Yagi efficiency
 

Art wrote:
"So just comparing the forward and rear lobe we have only achieved 50
per cent of our objective and this is not counting other losses."

Adding a director or reflector in the plane of a dipole can make it
nearly unidirectional. It will have forward gain over the dipole alone.
Adding more directors can increase forward gain. Losses of the radiator
and parasitic ellements to heat in them can be made small and antenna
efficiency high.

Best regards, Richard Harrison, KB5WZI

Yagi efficiency
 

art wrote:
Roy Lewallen wrote:

Since there's no "typical" Yagi, I presented one which most people would
consider to be worse than average -- one having only a 6 dB front/back
ratio. I also assumed for a starting point that the shape of the rear
lobe (that is, beamwidth and height) is the same as the front lobe. The
first calculation is to determine just what the ratio is of the powers
in the front and rear lobe. The answer is 4:1. That is, the front lobe
contains four times the power of the rear lobe.

I am not interested in front to back for what I am looking for but this
4:1 has my interest
What does it represent

I can't think how I can state it any more clearly than I did in the last
sentence of the text just above which you quoted.

and how did you get it?

When dealing with a power ratio, dB = 10 * log(ratio). Solving for ratio:

ratio = 10^(dB/10)

Here's where you'll probably need to get out that pocket calculator. dB
is 6 (see above text), so ratio = 10^(0.6) ~ 4.

Conversion between ratios and dB is a skill that anyone interested in
antennas should develop. I had assumed that it was part of the knowledge
required to pass a general class amateur exam, but apparently I was
mistaken. If the calculator operations are too complex for you, get a
chart of conversion factors which have already been calculated.

The rear usually has
more than one lobe

True. See the remainder of my previous posting for a discussion of this.

and the reflector ndestructs or deflects the energy to 90 degrees of
impact.

That's more nonsense. You'd develop a much better understanding of
antennas (or any physical system) by developing and learning to apply
some basic math skills than by dreaming up alternate explanations for
well-known physical phenomena.

I don't believe I can help you any more -- if indeed I've helped you at
all --, and think (or at least hope) that most other readers have
understood what I'm saying. So I'll bow out here.

Roy Lewallen, W7EL

Yagi efficiency
 

Terman treats decibels on page 8 of the 1955 third edition of
"Electronic and Radio Engineering".

The value of the decibel is 10 log of the power ratio.

When the ratio of the powers is 4, the decibel value is 6. This 6 dB
value applies among other things to doubling the distance between a
transmitting and receiving antenna. Half as many volts will be induced
in the receiver and will result in half as many amps. This is 1/4 the
power induced at half the distance between antennas..This may be
expressed as a positive power ratio of 4 to 1, or 6 dB.

Best regards, Richard Harrison, KB5WZI

Yagi efficiency
 

I had to ask rather than assume. My inclination where it came from
which you didn't say was that since the field produced by an actual
antenna is twice as great as the field produced by the isotropic
antenna the gain RATIO is two and the power gain is 2 squared which is
4. this means that to produce the same field strength at the same
distance, four times as much power would have to be supplied to an
isotropic radiator as to the actual antenna under consideration. But as
I stated many times RATIO as you are using it has not interest to me as
it is not relevant.
What you are doing is based on a RATIO at a given plane and that RATIO
changes with the plane examined. That is why the yagi is termed a
planar array In other words a reflector is used to affect a single
plane of radiation it is not all encompassing of the total rear
radiation. On top of all that the plane chosen is along the plane of
the main lobe only and does not in anyway include the ratio of the
second lobe to the rear or any nulls that are made. The rear radiation
fields is no way a mirror image of the forward radiated field. You are
supplying a conventional answer to a convential question which revolves
around a single plane where I am speaking of the total radiation field.
You can't keep trotting out the conventional answer to the question
that you want to be posed. I am sure glad I didn't guess where you were
getting the figure 4 from otherwise the thread would have been 200
posts long plus a lot of accusations as to who said what.Get back to
basics and stop trying to section the field of a dipole to make it
easier to simplify for newcomers, it does not represent factually
everything.
it is just a means to an end. without involvement in the toital "wave
and fields" subject
As I have oft times stated I am looking at the whole pattern in three
dimensional form and you keep trotting out answers based on a two
dimensional format
Art


,
Roy Lewallen wrote:
art wrote:
Roy Lewallen wrote:

Since there's no "typical" Yagi, I presented one which most people would
consider to be worse than average -- one having only a 6 dB front/back
ratio. I also assumed for a starting point that the shape of the rear
lobe (that is, beamwidth and height) is the same as the front lobe.

See, you are building a house on the basis of an assumption such that
instead of a rock
that you guessed was there it really was just sand.


The
first calculation is to determine just what the ratio is of the powers
in the front and rear lobe. The answer is 4:1. That is, the front lobe
contains four times the power of the rear lobe.

I am not interested in front to back for what I am looking for but this
4:1 has my interest
What does it represent

I can't think how I can state it any more clearly than I did in the last
sentence of the text just above which you quoted.

and how did you get it?

When dealing with a power ratio, dB = 10 * log(ratio). Solving for ratio:

ratio = 10^(dB/10)

Here's where you'll probably need to get out that pocket calculator. dB
is 6 (see above text), so ratio = 10^(0.6) ~ 4.

Conversion between ratios and dB is a skill that anyone interested in
antennas should develop. I had assumed that it was part of the knowledge
required to pass a general class amateur exam, but apparently I was
mistaken. If the calculator operations are too complex for you, get a
chart of conversion factors which have already been calculated.

The rear usually has
more than one lobe

True. See the remainder of my previous posting for a discussion of this.

and the reflector ndestructs or deflects the energy to 90 degrees of
impact.

That's more nonsense. You'd develop a much better understanding of
antennas (or any physical system) by developing and learning to apply
some basic math skills than by dreaming up alternate explanations for
well-known physical phenomena.

I don't believe I can help you any more -- if indeed I've helped you at
all --, and think (or at least hope) that most other readers have
understood what I'm saying. So I'll bow out here.

Roy Lewallen, W7EL

Yagi efficiency
 

"art" wrote in message
ups.com...
I had to ask rather than assume. My inclination where it came from
which you didn't say was that since the field produced by an actual
antenna is twice as great as the field produced by the isotropic
antenna the gain RATIO is two and the power gain is 2 squared which is
4. this means that to produce the same field strength at the same
distance, four times as much power would have to be supplied to an
isotropic radiator as to the actual antenna under consideration. But as
I stated many times RATIO as you are using it has not interest to me as
it is not relevant.
What you are doing is based on a RATIO at a given plane and that RATIO
changes with the plane examined. That is why the yagi is termed a
planar array In other words a reflector is used to affect a single
plane of radiation it is not all encompassing of the total rear
radiation. On top of all that the plane chosen is along the plane of
the main lobe only and does not in anyway include the ratio of the
second lobe to the rear or any nulls that are made. The rear radiation
fields is no way a mirror image of the forward radiated field. You are
supplying a conventional answer to a convential question which revolves
around a single plane where I am speaking of the total radiation field.
You can't keep trotting out the conventional answer to the question
that you want to be posed. I am sure glad I didn't guess where you were
getting the figure 4 from otherwise the thread would have been 200
posts long plus a lot of accusations as to who said what.Get back to
basics and stop trying to section the field of a dipole to make it
easier to simplify for newcomers, it does not represent factually
everything.
it is just a means to an end. without involvement in the toital "wave
and fields" subject
As I have oft times stated I am looking at the whole pattern in three
dimensional form and you keep trotting out answers based on a two
dimensional format
Art


then i would suggest learning some of the nitty gritty details of a program
like nec and figure out how to integrate it's field values over the 3d
surface and sort out the values you are interested in. no one here will do
that for you since it is normally not of interest in amateur antenna design.
we all understand how to evaluate the performance of antennas for our
'normal' uses in terms of gain and f/b ratio and how to read those 2d slices
to evaluate side lobes for our 'normal' uses. as you have stated it your
desire is not a normal one, you have special requirements which will require
a special solution that is not readily available for amateur antennas....
maybe that data is available for large satellite or deep space dishes where
they worry about extreme details of side lobe power and noise temperatures,
but not for hf ham use with normal antennas.

Yagi efficiency
 

On 29 Sep 2006 12:55:37 -0700, "art" wrote:

As I have oft times stated I am looking at the whole pattern in three
dimensional form and you keep trotting out answers based on a two
dimensional format

Art,

The same process in any plane reveals the same net result: you are not
going to achieve any more "efficiency" than that already offered by a
Yagi.

In fact, your design probably suffers extensively with regard to
"efficiency."

But no one knows this mystery design, do they? Sorry, but Fritz has
already cornered the market on flim-flam. He has probably been more
efficient about it too (if measured in sucker deposits).

73's
Richard Clark, KB7QHC

Yagi efficiency
 

On 29 Sep 2006 12:55:37 -0700, "art" wrote:

As I have oft times stated I am looking at the whole pattern in three
dimensional form and you keep trotting out answers based on a two
dimensional format

Art,

As I re-consider this statement, I don't believe you at all. The
earliest solutions to your "problem" were satisfied by stacked yagis.
They also answer what you complain of above as well. Bay arrangements
of yagis go even further. As they are skeletal versions of a massive
dipole array against a screen, all are solutions that are merely the
natural consequence of massive duplication and constructive phase
shift.

This stuff has been around for half a century or more and you have yet
to reveal anything new, much less a method that transcends existing
knowledge. If you had more experience in using modelers, and
examining the history of antenna design, then you could confidently
make the statement above. However, nothing in your correspondence
even reveals you understand the fundamentals beyond parroting phrases
cut and paste from other sources.

73's
Richard Clark, KB7qHC

Yagi efficiency
 

"art" wrote in 1159495614.320553.169910
@i42g2000cwa.googlegroups.com:


Let us look at a common dipole with a reflector, the planar view of
radiation which ignores radiation outside the plane is a figure 8


For the sake of the arguement, let's say we're feeding the antenna with
100W, so 50W goes one way, and 50W goes the other way. Correct?


where the addition of a reflector does nothing to enhance increased
forward radiation


Now the 50W going towards the reflector... What happens to it? Heat?
Reflected back down the feed line? (Sorry...)


so immidiately we can say that the forward lobe achieves what
is termed a major lobe plus other forward lobes outside of the main
lobe where as the radiation to the rear achieves nothing that enhances
the forward main lobe.


So the most efficient antenna is the isotropic, because its radiating
volume is a sphere. Next would be a dipole, then a vertical, and then
a yagi with just 1 parasitic element, and getting worse as you add
elements, because each element is shaving a bit off the volume.

Correct?

--
David Hatch
KR7DH

Yagi efficiency
 

David Hatch wrote:
"art" wrote in 1159495614.320553.169910
@i42g2000cwa.googlegroups.com:


Let us look at a common dipole with a reflector, the planar view of
radiation which ignores radiation outside the plane is a figure 8


For the sake of the arguement, let's say we're feeding the antenna with
100W, so 50W goes one way, and 50W goes the other way. Correct?


where the addition of a reflector does nothing to enhance increased
forward radiation


Now the 50W going towards the reflector... What happens to it? Heat?
Reflected back down the feed line? (Sorry...)


so immidiately we can say that the forward lobe achieves what
is termed a major lobe plus other forward lobes outside of the main
lobe where as the radiation to the rear achieves nothing that enhances
the forward main lobe.


So the most efficient antenna is the isotropic, because its radiating
volume is a sphere. Next would be a dipole, then a vertical, and then
a yagi with just 1 parasitic element, and getting worse as you add
elements, because each element is shaving a bit off the volume.

Correct?

--
David Hatch
KR7DH

It is true that a vertical monopole antenna will have a larger total
footprint of coverage than a yagi. If the earth was evenly coated with
ham radio operators I could probably make more contacts using a
vertical monopole than I could a yagi that could not be rotated.

Yagi efficiency
 

I believe you are correct.
If you understand the question posted over a 100 posts ago why is it
that others are stumbling.
I could not figure out how to determine the volume mathematically so I
took the model making route which confirms the poor efficiency of the
yagi. What blows my mind is the assertion that the major lobe is a
large fraction of the total volume whatever a large fraction really
means ( no hints given by the poster) plus the idea that volume outside
the main lobe is miniscule,.Seems like memorisation of required answers
is the way to go with amateur radio at the moment. Thinking from first
principles obviously not required just give an answer that you want to
give regardless what the question was and then blame the poster because
he didn't pose the correct question for which the answer was well
suited.
If you can't provide an answer then change the subject and then discuss
that
Well I am glad somebody read that first post for what it said not for
what most wanted to read. I feel a lot better now
Art






Dave wrote:
"art" wrote in message
ups.com...
I had to ask rather than assume. My inclination where it came from
which you didn't say was that since the field produced by an actual
antenna is twice as great as the field produced by the isotropic
antenna the gain RATIO is two and the power gain is 2 squared which is
4. this means that to produce the same field strength at the same
distance, four times as much power would have to be supplied to an
isotropic radiator as to the actual antenna under consideration. But as
I stated many times RATIO as you are using it has not interest to me as
it is not relevant.
What you are doing is based on a RATIO at a given plane and that RATIO
changes with the plane examined. That is why the yagi is termed a
planar array In other words a reflector is used to affect a single
plane of radiation it is not all encompassing of the total rear
radiation. On top of all that the plane chosen is along the plane of
the main lobe only and does not in anyway include the ratio of the
second lobe to the rear or any nulls that are made. The rear radiation
fields is no way a mirror image of the forward radiated field. You are
supplying a conventional answer to a convential question which revolves
around a single plane where I am speaking of the total radiation field.
You can't keep trotting out the conventional answer to the question
that you want to be posed. I am sure glad I didn't guess where you were
getting the figure 4 from otherwise the thread would have been 200
posts long plus a lot of accusations as to who said what.Get back to
basics and stop trying to section the field of a dipole to make it
easier to simplify for newcomers, it does not represent factually
everything.
it is just a means to an end. without involvement in the toital "wave
and fields" subject
As I have oft times stated I am looking at the whole pattern in three
dimensional form and you keep trotting out answers based on a two
dimensional format
Art


then i would suggest learning some of the nitty gritty details of a program
like nec and figure out how to integrate it's field values over the 3d
surface and sort out the values you are interested in. no one here will do
that for you since it is normally not of interest in amateur antenna design.
we all understand how to evaluate the performance of antennas for our
'normal' uses in terms of gain and f/b ratio and how to read those 2d slices
to evaluate side lobes for our 'normal' uses. as you have stated it your
desire is not a normal one, you have special requirements which will require
a special solution that is not readily available for amateur antennas....
maybe that data is available for large satellite or deep space dishes where
they worry about extreme details of side lobe power and noise temperatures,
but not for hf ham use with normal antennas.

Yagi efficiency
 

art wrote:
I believe you are correct.
If you understand the question posted over a 100 posts ago why is it
that others are stumbling.
I could not figure out how to determine the volume mathematically so I
took the model making route which confirms the poor efficiency of the
yagi. What blows my mind is the assertion that the major lobe is a
large fraction of the total volume whatever a large fraction really
means ( no hints given by the poster) plus the idea that volume outside
the main lobe is miniscule,.Seems like memorisation of required answers
is the way to go with amateur radio at the moment. Thinking from first
principles obviously not required just give an answer that you want to
give regardless what the question was and then blame the poster because
he didn't pose the correct question for which the answer was well
suited.
If you can't provide an answer then change the subject and then discuss
that
Well I am glad somebody read that first post for what it said not for
what most wanted to read. I feel a lot better now
Art






Dave wrote:
"art" wrote in message
ups.com...
I had to ask rather than assume. My inclination where it came from
which you didn't say was that since the field produced by an actual
antenna is twice as great as the field produced by the isotropic
antenna the gain RATIO is two and the power gain is 2 squared which is
4. this means that to produce the same field strength at the same
distance, four times as much power would have to be supplied to an
isotropic radiator as to the actual antenna under consideration. But as
I stated many times RATIO as you are using it has not interest to me as
it is not relevant.
What you are doing is based on a RATIO at a given plane and that RATIO
changes with the plane examined. That is why the yagi is termed a
planar array In other words a reflector is used to affect a single
plane of radiation it is not all encompassing of the total rear
radiation. On top of all that the plane chosen is along the plane of
the main lobe only and does not in anyway include the ratio of the
second lobe to the rear or any nulls that are made. The rear radiation
fields is no way a mirror image of the forward radiated field. You are
supplying a conventional answer to a convential question which revolves
around a single plane where I am speaking of the total radiation field.
You can't keep trotting out the conventional answer to the question
that you want to be posed. I am sure glad I didn't guess where you were
getting the figure 4 from otherwise the thread would have been 200
posts long plus a lot of accusations as to who said what.Get back to
basics and stop trying to section the field of a dipole to make it
easier to simplify for newcomers, it does not represent factually
everything.
it is just a means to an end. without involvement in the toital "wave
and fields" subject
As I have oft times stated I am looking at the whole pattern in three
dimensional form and you keep trotting out answers based on a two
dimensional format
Art


then i would suggest learning some of the nitty gritty details of a program
like nec and figure out how to integrate it's field values over the 3d
surface and sort out the values you are interested in. no one here will do
that for you since it is normally not of interest in amateur antenna design.
we all understand how to evaluate the performance of antennas for our
'normal' uses in terms of gain and f/b ratio and how to read those 2d slices
to evaluate side lobes for our 'normal' uses. as you have stated it your
desire is not a normal one, you have special requirements which will require
a special solution that is not readily available for amateur antennas....
maybe that data is available for large satellite or deep space dishes where
they worry about extreme details of side lobe power and noise temperatures,
but not for hf ham use with normal antennas.

The major lobe is a very large portion of the total power, it has been
figured out but I doubt if anyone wants to figure it out again for any
particular yagi. I know I could care less, but it is obvious from
looking at the plotted radiation patterns that sidelobe power is very
small amount easily in the 2% ball park of the total amount. Of course
some yagis will be better at concentratining the power in the main
lobe than others. By the way ther is 3d yagi antenna pattern
information available. Just find plots for the antenna mounted
horizontally and vertically. This is something almost any antenna
simulation program can provide.

Yagi efficiency
 

JIMMIE wrote:
art wrote:
I believe you are correct.
If you understand the question posted over a 100 posts ago why is it
that others are stumbling.
I could not figure out how to determine the volume mathematically so I
took the model making route which confirms the poor efficiency of the
yagi. What blows my mind is the assertion that the major lobe is a
large fraction of the total volume whatever a large fraction really
means ( no hints given by the poster) plus the idea that volume outside
the main lobe is miniscule,.Seems like memorisation of required answers
is the way to go with amateur radio at the moment. Thinking from first
principles obviously not required just give an answer that you want to
give regardless what the question was and then blame the poster because
he didn't pose the correct question for which the answer was well
suited.
If you can't provide an answer then change the subject and then discuss
that
Well I am glad somebody read that first post for what it said not for
what most wanted to read. I feel a lot better now
Art






Dave wrote:
"art" wrote in message
ups.com...
I had to ask rather than assume. My inclination where it came from
which you didn't say was that since the field produced by an actual
antenna is twice as great as the field produced by the isotropic
antenna the gain RATIO is two and the power gain is 2 squared which is
4. this means that to produce the same field strength at the same
distance, four times as much power would have to be supplied to an
isotropic radiator as to the actual antenna under consideration. But as
I stated many times RATIO as you are using it has not interest to me as
it is not relevant.
What you are doing is based on a RATIO at a given plane and that RATIO
changes with the plane examined. That is why the yagi is termed a
planar array In other words a reflector is used to affect a single
plane of radiation it is not all encompassing of the total rear
radiation. On top of all that the plane chosen is along the plane of
the main lobe only and does not in anyway include the ratio of the
second lobe to the rear or any nulls that are made. The rear radiation
fields is no way a mirror image of the forward radiated field. You are
supplying a conventional answer to a convential question which revolves
around a single plane where I am speaking of the total radiation field.
You can't keep trotting out the conventional answer to the question
that you want to be posed. I am sure glad I didn't guess where you were
getting the figure 4 from otherwise the thread would have been 200
posts long plus a lot of accusations as to who said what.Get back to
basics and stop trying to section the field of a dipole to make it
easier to simplify for newcomers, it does not represent factually
everything.
it is just a means to an end. without involvement in the toital "wave
and fields" subject
As I have oft times stated I am looking at the whole pattern in three
dimensional form and you keep trotting out answers based on a two
dimensional format
Art


then i would suggest learning some of the nitty gritty details of a program
like nec and figure out how to integrate it's field values over the 3d
surface and sort out the values you are interested in. no one here will do
that for you since it is normally not of interest in amateur antenna design.
we all understand how to evaluate the performance of antennas for our
'normal' uses in terms of gain and f/b ratio and how to read those 2d slices
to evaluate side lobes for our 'normal' uses. as you have stated it your
desire is not a normal one, you have special requirements which will require
a special solution that is not readily available for amateur antennas....
maybe that data is available for large satellite or deep space dishes where
they worry about extreme details of side lobe power and noise temperatures,
but not for hf ham use with normal antennas.

The major lobe is a very large portion of the total power, it has been
figured out but I doubt if anyone wants to figure it out again for any
particular yagi. I know I could care less, but it is obvious from
looking at the plotted radiation patterns that sidelobe power is very
small amount easily in the 2% ball park of the total amount. Of course
some yagis will be better at concentratining the power in the main
lobe than others. By the way ther is 3d yagi antenna pattern
information available. Just find plots for the antenna mounted
horizontally and vertically. This is something almost any antenna
simulation program can provide.


Like other I didnt understand the equestion as origionally posted
either. This was probably due to your false statement requardinding the
efficency or lack there of as you define efficentcy
of a yagi antenna. AS you say that you can take a look at an antenna
plot see that it is obviously inefficent without showing the mathmatics
I can look at one and tell you it is very efficent per your own
definition without giving the numbers. I can only assume you are
confused by the fact the plots are drawn with a LOG scale as opposed to
a linear scale. If drawn using a linear scale the side lobes would be
1/100 to 1/1000 the size of the main beam. If you dont want to take my
word for simply take any yagi antenna plot and redraw it to a linear
scale.

Yagi efficiency
 

art wrote:

Cecil, efficiency depends on what your objectives are
snip bull****
Art.

Art

You are obviously much smarter than every one here combined. So I will
leave it up to you to design the antenna(s) that no one has been able to
come up with before this miracle antenna you envision. The tens of
millions of man hours we have put into antenna developement cannot
possibly equal your intelligence.

Prove everyone wrong. Go ahead. We're waiting.

tom
K0TAR

Yagi efficiency
 

Richard Clark wrote:

On 29 Sep 2006 05:47:14 -0700, "art" wrote:


one having only a 6 dB front/back ratio.


But that 4:1 figure where does it come from?


Hi Art,

Do you know how to work a calculator using logarithms?

73's
Richard Clark, KB7QHC

Yagi efficiency
 

Richard Clark wrote:

On 29 Sep 2006 05:47:14 -0700, "art" wrote:


one having only a 6 dB front/back ratio.


But that 4:1 figure where does it come from?


Hi Art,

Do you know how to work a calculator using logarithms?

73's
Richard Clark, KB7QHC

Which reminds me, I wanted to start a thread on calculators.

tom
K0TAR

Yagi efficiency
 

Tom Ring wrote:

SNIPPED


Which reminds me, I wanted to start a thread on calculators.

tom
K0TAR

Calculator: definition - One person with one brain, one pencil, one piece of
paper, and knowledge of math [Oh my gosh! I'll have to spend time learning
something. Does that mean I'll have to study to get a license?]

Yagi efficiency
 

art wrote:
Dan,
you know quite well what the post that started this thread asked for.
I only added the TOA comments to fill in some body where I was
coming from not for advice on what antenna to build.
People are quibling over the word "efficiency" which I find rather
wierd
especially since I am supposed to be in the company of fellow
engineers.

Interesting Art, you find that weird, and I find it as an explanation! 8^)

- 73 de Mike KB3EIA -