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