Jerry Martes wrote:
...
How do you define efficiency?

Jerry



Jerry:

You make that sound like such a simple question.

Antenna efficiency is a complicated and often misused figure.

All antennas suffer from losses. A simple horn antenna for example will
not be as efficient as a perfect aperture of the same size because of
phase offset. The real efficiency of an antenna combines impedance match
with other factors such as aperture and radiation efficiency to give the
overall radiated signal for a given input. The best and mostwidely used
expression of this efficiency is to combine overall efficiency with
directivity (of the antenna) and express the efficiency times
directivity as gain.


The above is NOT mine, but taken from the web...
http://www.tmcdesign.com/antenna%20c...nformation.htm

So, we need to know if we are discussing antenna efficiency, or
radiation efficiency, or the skin effect as related to the ether
efficiency, etc. grin

Good that you are asking him!

Regards,
JS

"John Smith" wrote in message
...
Jerry Martes wrote:
...
How do you define efficiency?

Jerry



Jerry:

You make that sound like such a simple question.

Antenna efficiency is a complicated and often misused figure.

All antennas suffer from losses. A simple horn antenna for example will
not be as efficient as a perfect aperture of the same size because of
phase offset. The real efficiency of an antenna combines impedance match
with other factors such as aperture and radiation efficiency to give the
overall radiated signal for a given input. The best and mostwidely used
expression of this efficiency is to combine overall efficiency with
directivity (of the antenna) and express the efficiency times directivity
as gain.


The above is NOT mine, but taken from the web...
http://www.tmcdesign.com/antenna%20c...nformation.htm

So, we need to know if we are discussing antenna efficiency, or radiation
efficiency, or the skin effect as related to the ether efficiency, etc.
grin

Good that you are asking him!

Regards,
JS

Hi John

It really *is* a simple question. Again, how is Efficienct being defined
for this investigation?? As you have written, that question has to be
answered by Art, the original poster, ?doesnt it?

I was a little embarrassed because that "definition" of gain in the
referenced site was really difficult for me to understand. I really admire
you guys who understand phrases like "phase offset" as related to
efficiency.

Jerry

For those who wish to actually learn and not just insult each other,
get a calculator, learn how to calculate Cosine Theta a trivial math
problem that any 9th grader can be taught in 5 minutes flat, get a BIG
piece of paper reason to come, and actually calculate the shape and
vector length of the lobes of a two element Yagi-Uda antenna... Do the
calculation in both the horizonal and vertical planes... From that you
can calculate the volume of each lobe, which is proportional to the
percentage of power in each lobe... From that number you can very
simply calculate what percentage went into the lobes you prefer and
what went in the lobes you don't prefer...

Now, the reason for the BIG piece of paper... The antenna patterns you
see on the screen with EZNEC, or in the antenna handbooks, are
logarithmic, not linear and there are flavors to them, ARRL, linear
logarithmic, modified logarithmic... So, the patterns are
distorted... Why is that? Because if they were linear and the front
lobe and the rear lobe are to the same scale the front lobe will take
up the entire length of the screen/paper and the rear lobe will need a
magnifying glass to be seen... A rear lobe that is 20dB down from the
front lobe is down by the power ratio of 100... So, if your forward
lobe calculates out to be 10 inches long, the rear lobe will be be 1/10
of an inch.... I'll let you figure out the size of a lobe that is 30dB
down (get out your microscope)

For those who want to review do a search on Joseph Reisert, who has
published numerous writings on antennas and patterns... There many are
others also, but Joe is published on the web, and very readable...

cheers ... denny / k8do

"Denny" wrote in message
oups.com...
For those who wish to actually learn and not just insult each other,
get a calculator, learn how to calculate Cosine Theta a trivial math
problem that any 9th grader can be taught in 5 minutes flat, get a BIG
piece of paper reason to come, and actually calculate the shape and
vector length of the lobes of a two element Yagi-Uda antenna... Do the
calculation in both the horizonal and vertical planes... From that you
can calculate the volume of each lobe, which is proportional to the
percentage of power in each lobe... From that number you can very
simply calculate what percentage went into the lobes you prefer and
what went in the lobes you don't prefer...

Now, the reason for the BIG piece of paper... The antenna patterns you
see on the screen with EZNEC, or in the antenna handbooks, are
logarithmic, not linear and there are flavors to them, ARRL, linear
logarithmic, modified logarithmic... So, the patterns are
distorted... Why is that? Because if they were linear and the front
lobe and the rear lobe are to the same scale the front lobe will take
up the entire length of the screen/paper and the rear lobe will need a
magnifying glass to be seen... A rear lobe that is 20dB down from the
front lobe is down by the power ratio of 100... So, if your forward
lobe calculates out to be 10 inches long, the rear lobe will be be 1/10
of an inch.... I'll let you figure out the size of a lobe that is 30dB
down (get out your microscope)

For those who want to review do a search on Joseph Reisert, who has
published numerous writings on antennas and patterns... There many are
others also, but Joe is published on the web, and very readable...

cheers ... denny / k8do

Hi Denny

Does Joseph Reisert define Efficiency as applied to this question about
Yagi antennas?

Jerry

As soon as you explain what you mean by "efficiency" I can answer that
in detail..

What do you mean by efficiency? Is efficiency 100% of applied power
being in the forward lobe and 0% in sidelobes or rear lobes? If so,
better get a new hobby because it ain't gonna happen... Can't happen
due to the laws of physics... For discussion I'm going to assume that
this is your goal... Let's go up a bit in frequency where the antennas
are small and easy to work with... Telescopes... The only difference
between blue light and 20 meters is the frequency...

Now those telescopes are some really high gain antennas.. So, here we
have this super, duper, high gain antenna (I don't know what the gain
in DBI is, but it is huge, man, huge)... And we point it at a really
faint signal, say the star Rigel - which is an Isotropic radiator - a
point source... And we adjust the resonance (focus) for the best
possible signal we can get... We put a slit on the telescope and scan
across that signal and gasp it has side lobes! Not all the power
luminence is in the main lobe... Mathematically there will always be
side lobes off the main lobe... By reciprocity, it is impossible to
focus a point souce of light down to a point... The center brilliance
will be sorrounded by circles of confusion lobes... Like wise it is
impossible to build an antenna that has a response that is only a
single main lobe and no side lobes...

'Now, we can build arrays of antennas that enhance the main lobe and
diminish the side and rear lobes through pattern multiplication, and we
can get those unwanted lobes down to a few thousandths of the power in
the main lobe... One way is a broadside array of six of a dozen, or so,
more point sources with half wave spacing and fed in Quadrature, or
other current variations... Krause's book has a good set of patterns
and explanation of this method of synthesizing an antenna that is very
"efficient"... efficiency being defined as I 'assumed' above...
However, these antennas are not efficient in terms of time, labor,
size, cost, and complexity...

So, to reiterate, go to Reisert, and Krause, and Terman, et. al. to
find your magically 'efficient' antenna...

denny / k8do

btw, a thought just caught me... W8JI on his web site has a great table
of antenna 'efficiency' in low noise receiving antennas... Maybe this
is what you mean... GO look it up..

"Denny" wrote in message
oups.com...
As soon as you explain what you mean by "efficiency" I can answer that
in detail..

What do you mean by efficiency? Is efficiency 100% of applied power
being in the forward lobe and 0% in sidelobes or rear lobes? If so,
better get a new hobby because it ain't gonna happen... Can't happen
due to the laws of physics... For discussion I'm going to assume that
this is your goal... Let's go up a bit in frequency where the antennas
are small and easy to work with... Telescopes... The only difference
between blue light and 20 meters is the frequency...

Now those telescopes are some really high gain antennas.. So, here we
have this super, duper, high gain antenna (I don't know what the gain
in DBI is, but it is huge, man, huge)... And we point it at a really
faint signal, say the star Rigel - which is an Isotropic radiator - a
point source... And we adjust the resonance (focus) for the best
possible signal we can get... We put a slit on the telescope and scan
across that signal and gasp it has side lobes! Not all the power
luminence is in the main lobe... Mathematically there will always be
side lobes off the main lobe... By reciprocity, it is impossible to
focus a point souce of light down to a point... The center brilliance
will be sorrounded by circles of confusion lobes... Like wise it is
impossible to build an antenna that has a response that is only a
single main lobe and no side lobes...

'Now, we can build arrays of antennas that enhance the main lobe and
diminish the side and rear lobes through pattern multiplication, and we
can get those unwanted lobes down to a few thousandths of the power in
the main lobe... One way is a broadside array of six of a dozen, or so,
more point sources with half wave spacing and fed in Quadrature, or
other current variations... Krause's book has a good set of patterns
and explanation of this method of synthesizing an antenna that is very
"efficient"... efficiency being defined as I 'assumed' above...
However, these antennas are not efficient in terms of time, labor,
size, cost, and complexity...

So, to reiterate, go to Reisert, and Krause, and Terman, et. al. to
find your magically 'efficient' antenna...

denny / k8do

btw, a thought just caught me... W8JI on his web site has a great table
of antenna 'efficiency' in low noise receiving antennas... Maybe this
is what you mean... GO look it up..


Hi Denny

You seemed to have missed the point completely. Maybe your news reader
didnt supply you with the original post where Art refers to Efficiency of a
Yagi as being low.
Art finally agreed that the efficiency he refers to with his Yagi is the
Power IN divided by Power Out kind of efficiency. Since I consider the
statement that the Yagi antenna is I squared R lossy to be entirely
erroneous, I realized that I had no place in such a frivilous discussion.
Now I find it difficult to understand why you want to write so extensively
about telescopes, and broadside arrays, and sidelobes when we are
considering Efficiency. You may want to refer to Apperature Efficiency,
but, you are doing a poor job of it.

Whats with you Denny??? Why do you think of yourself as so superior that
you raise your voice at me telling me to "GO look it up".

Jerry

Jerry, if I came across a bit loud I apologize.. I usually skim down
the latest chatter and then just post to the group off the bottom
message, often having no direct bearing on the particular post it spins
off from... Also, I skim a number of groups and topics and I run a
business so I can miss a post that puts a different spin on things...
If I ruffled your feathers it was not intentional...
Let me comment that I absolutely agree with you that claiming a Yagi is
inefficient from the perspective of I2R losses shows a lack of basic
knowledge... Having said that, let me also note that closing the
spacing, i.e. tighter than the classical Yagi-Uda array, and putting
the beam into Supergain territory has consequences... Moxon has a non
mathematical discussion of the supergain antennas with a graph of
spacing v/s gain v/s impedence, and I Krauss mentioned that he designed
his flat top array stimulated from a paper by Brown (I think it was)
where he discussed arrays that have more than additive gain by tight
spacing... Anyway I digress; the point of all this mumble is that these
supergain "Yagi" arrays can have quite high I2R losses... But the
commercial Yagi-Uda today is not in that class...

Anyway, Cheers ... denny / k8do

ORIGINAL MESSAGE:

On 2 Dec 2006 05:36:05 -0800, "Denny" wrote:


For those who wish to actually learn and not just insult each other,
get a calculator, learn how to calculate Cosine Theta a trivial math
problem that any 9th grader can be taught in 5 minutes flat, get a BIG
piece of paper reason to come, and actually calculate the shape and
vector length of the lobes of a two element Yagi-Uda antenna... Do the
calculation in both the horizonal and vertical planes... From that you
can calculate the volume of each lobe, which is proportional to the
percentage of power in each lobe... From that number you can very
simply calculate what percentage went into the lobes you prefer and
what went in the lobes you don't prefer...
snip

------------ REPLY FOLLOWS ------------

The problem here is not math, it's English. You are calculating gain
and/or directivity, not efficiency.

Bill, W6WRT

Bill Turner wrote:

On 2 Dec 2006 05:36:05 -0800, "Denny" wrote:
... From that number you can very
simply calculate what percentage went into the lobes you prefer and
what went in the lobes you don't prefer...

The problem here is not math, it's English. You are calculating gain
and/or directivity, not efficiency.

Maybe beam efficiency? (cone beam power)/(total radiated power)
--
73, Cecil http://www.w5dxp.com

Cecil Moore wrote:

Bill Turner wrote:


On 2 Dec 2006 05:36:05 -0800, "Denny" wrote:

... From that number you can very
simply calculate what percentage went into the lobes you prefer and
what went in the lobes you don't prefer...


The problem here is not math, it's English. You are calculating gain
and/or directivity, not efficiency.


Maybe beam efficiency? (cone beam power)/(total radiated power)

C'mon Cecil, you know exactly what efficiency is!

[Pin - Ploss}/Pin

All other "definitions" are red herrings and do not contribute to the answer.