"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.

art wrote:
When one looks at a.radiating array pattern one can see that the yagi
is very inefficient. Does anybody know of the relative volume
contained in the main radiation lobe versus the total volume of the
entire
pattern? I know there are a lot of different type antenna gains and
arrangement but I am trying to determine in an informal way the
efficiency
ratio and compare it to what would appear to be a very efficient
antenna
such as a dish. A casual look at a yagi radiation pattern would suggest


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

that it is less than 50% efficient at best especially when considering
DX work
where even the main lobe is less than 50% efficient when looking at
available
signal paths beyond 4000 miles which are somewhat below 12 degrees and
where the main lobe itself is centered between 13 and 14 degrees with
an
average amateur antennah
Art

On 26 Sep 2006 10:31:14 -0700, "Zack" 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

Hi Zack,

You may be confusing (or have been confused with the content of this
thread) antenna effeciency with system efficiency. The page makes the
point of there being a feed "appropriateness." I would suspect the
method of feed makes the difference (and those issues that lie beyond
that include method of detection, noise, and so on).

As for putting it to the antenna's merit, the roughness is far more
significant to shorter wavelengths (roughness is on order of eight
wave). This in itself produces problems of phase control, and phase
control is the name of the game in directivity.

73's
Richard Clark, KB7QHC

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

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

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

"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

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

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