Yagi efficiency
 

"art" wrote in message
ps.com...
Hi Jerry sorry that I didn't respond to you earlier but here goes
untuned elements which haveWhen you decide to get something going you
need a means to get there.
When you decide on the means you need to know if you are expending the
minimum energy to get there
In this particular case we have decided on generating a time varying
field around some reradiatiung elements to obtain a radiating field of
some sort Since we are applying energy
to elements we want to know if the elements are doing a good job or are
they losing out on energy translation by generating heat e.t.c instead
of it all going where I want it to. So what we do is find out what
energy we put in to obtain our objective and measure what we got out
towards our objective to see how effective we were which is a measure
of efficiency... Ideally we dont want to produce heat and all that
other stuff but the anteena array that we have chosen to do this is a
yagi array of elements which starts of with a resonant dipole which has
a purely resistive impedance. But the yagi then goes on to upset things
by adding which have a reactive impedance which detracts from the purly
resistive value of the impedance which means losses when we should have
added extra resonant elements to the set up as a means of adding to the
structure to maintain zero losses BUT the yagi does go a long way
towards our objectives so it has hung around for a long while. As a
side issue
we should also consider the environment that our array is working in
and also the type of element material we are using as well as the means
taken to input power but that gets more complicated so the question is
really revolving around the energy input versus a magnetic near field
generation that goes on to form a far field radiation field.
SOOOOOOOooooo
efficiency in this case compares the electrical power applied to the
yagi to generate a magnetic and electric fieldaround the yagi and to
check how much energy was lost on the way to our objective. Sorry for
the delay but fortunately I did check back in before I moved on to
other things
Regards
Art





Jerry Martes wrote:
Hi Art

You know, I am really a slow learner. I still dont understand how
efficiency is defined. Can you try again to teach me how efficiency is
defined??

Thanks
Jerry



"art" wrote in message
ups.com...
Hi Jerry perhaps I am wrong that there ARE people who want to talk
antennas
We went thru this some time ago and I was referring to efficiency of
the yagi antenna
with respect to the radiation field where much is reflected to areas of
no concern.
Others did not like this and said efficiency referred to is one of the
radiation facets of a radiating array and the yagi is efficient and
then the sniping statrted and the newsgroup went down hill as others
joined to emulate and perpetuate abrasive non antenna related
subjects. I just popped back to see if the group wanted to change back
to antenna talk
and posted the term efficiency of the yagi in terms of radiation which
everybody was
auguing about. Well things haven't changed they still just want to
throw stones and more will join in as the thread goes on., Ill stick it
out for an hour or so and then move on again.
Cant wait for somebody to compare with free space stuff to add to the
confusion, I know it will come




Jerry Martes wrote:
"art" wrote in message
ups.com...
Some time ago I mentioned how inefficient Yagi design
antennas were thinking more in the way of how little of
the radiation used got to its required direction.
At that time people said the antenna was efficient though
they wanted to talk about
actual radiation efficiency and the sniping began
.Nobody but nobody came back with the radiation
efficiency of a Yagi as they saw the question, they
just wanted to throw stones.Imagine that antennas
was not what the experts wanted to talk about and
the newsgroup took a turn for the worst
So I join in with the thoughts of radiation efficiency
of a yagi unless you prefere to give up this antenna
newsgroup. But before you scream out and throw
stones again I will referr to efficiency as most of the
members of this group what's left of them think of the term.
So let's look at that if that is what you preferr..

The basic small yagi has three elements one driven,
one a reflector and one a director yet only one
element has a truly resistive impedance whereas
the other two do not. Since two elements out of the
three are producing reactive impedances and wherein
the reactive portions of impedance is pure waste
pray tell me how one can consider a yagi as efficient?
And please, please don't waste time on "I don't understand"
otherwise everything drops down to the subject of spark noise
which was really decided by hams a long while ago.
On the other side of the coin, if the reactive portion of an
impedance is not waste then why is LCR
type mesh circuitry only revolve around lumped circuitry?
HINT add up the power emminating from each element
P =I sq times real resistance for those who are just followers.

There again maybe it is best that you be honest and say
you don't understand! Better that than join those who have
nothing to say about antennas!


Hi Art

OK, I dont understand. Perhaps I could begin to understand if I
was
given the definition of efficiency we are using in this discussion.
How
do
you define efficiency?

Jerry



At resonance it is the antenna as a whole that is resistive not just the
driven element.

Yagi efficiency
 

"art" wrote in message
oups.com...
Help me help me please , a detuned element has a reactive impedance
value, simple fact.
Now with your superior knowledge and education show not just me but all
of us how the production of a reactive impedance does not or cannot
impede the formation of emmited flux? I dont want just comments or
guesses just an explanation of your position which aligns with the laws
of Kirchoff, Ampere, Green ,Laplace etc as a group or as single people
to give your response some credability . Cecil has given you a starting
point as to what exactly reactance is so the rest should be easy for
you considering how easily you can dismiss my logic and education
regarding the Yagi antenna. Bill I cant wait to hear the mutterings of
a master of your station, a chance to learn something really new, maybe
not even written in a book Go man go! Well I know you can't.... but I
am just demonstrating that if you want to snipe then others will be
encouraged to snipe and it is not nice. Knoweledge is what I am after
not errent gun shots



Bill Turner wrote:
ORIGINAL MESSAGE:

On 1 Dec 2006 18:29:51 -0800, "art" wrote:


Since two elements out of the
three are producing reactive impedances and wherein
the reactive portions of impedance is pure waste
pray tell me how one can consider a yagi as efficient?

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

Please let us know what electronics school you attended so we can
avoid it like the plague and, if at all possible, have it
de-certified.

Thanks,

Bill, W6WRT

I have a better idea Art, since you are the ones making the claims why dont
you use these references to show your claims are correct. Subject yourself
to the same terms as you expect of others. Must of us have better things to
do than convince a green wall it is really green and not blue.

Yagi efficiency
 

art wrote:

David are you going nuts? I used the word impedance whichcan mean two
components only one of which is used for power.

No! You used the phrase "reactive impedance".

That is significantly different from "Complex Impedance"!

XL [2*Pi*f*L] is a reactive impedance, not a complex impedance!

XC [1/(2*Pi*f*C)] is a reactive impedance, not a complex impedance.

R[Rr + Rloss] + j[XL] is a complex impedance.

I still say you're using technical definitions that do not conform to the
standard definitions.

Yagi efficiency
 

"art" wrote in message
Really Cecil I am trying to get people to think
about elements containing inherranr directional properties so that
uneeded radiation is harnessesd for useful purposes but they are
shutting their ears.
__________________

Art,

The dipole elements (of all lengths) in a Yagi _do_ have their own
directional properties, and generate their own radiation patterns -- the
fields of which add/subtract in space as a function of their relative
magnitudes and phases to produce a net field that varies around the
radiation sphere centered on the antenna.

From reading between the lines, maybe you are relating antenna efficiency to
the free-space field strength that the antenna produces at a given distance
and direction in the far field when a given amount of r-f power is applied
to its input terminals, compared to the field produced for the same
conditions by a reference radiator such as a 1/2-wave dipole, or an
isotropic source.

For this definition it is reasonable to expect that both the test and the
reference antenna have negligible conductor and dielectric loss, and that
they both present a return loss of 30 dB or better to the transmission line
leading to the transmitter. All of that is practical to achieve. Also note
under these conditions that a return loss of 30 dB means that 99.9% of the
power applied to the antenna is radiated (somewhere), so if that is the
meaning of antenna efficiency, it is high indeed.

By this definition, the efficiency of a Yagi in its direction of maximum
field is very high, and does not indicate that sub-optimal choices were made
for its mechnical layout. In fact, the inventors of this antenna and many
others have spent much time and effort with physical and electrical models
of the Yagi to optimize its patterns and gains. The result of all that
finds that the director(s) should be shorter than the driven element, that
the reflector should be longer, and that using more than one reflector has
minimal effect. That is the "bottom line," and speculation to the contrary
won't change it.

Using this Yagi design and this definition of efficiency, a standard,
6-element Yagi has a main lobe peak efficiency of about 250% compared to a
1/2-wave dipole, and 316% compared to an isotropic radiator, which
correspond to radiated power ratios of about 610% and 1,000%, respectively.

IEEE Standard 145-1983 gives the standard definitions of terms for antennas
(gain, directivity, efficiency etc).

RF

Yagi efficiency
 

"Richard Fry" wrote in message
...
"art" wrote in message
Really Cecil I am trying to get people to think
about elements containing inherranr directional properties so that
uneeded radiation is harnessesd for useful purposes but they are
shutting their ears.

every thing that radiates has 'inherent directional properties'. it is
those properties that software like nec models. adding up all the
contributions of lots of little tiny pieces of radiating current is what
goes into designing all sorts of antennas, including yagis. there is no
magic wire that is going to get more power on target, no strange property
that is going to give you super gain, and no way to get rid of all the
'uneeded radiation'. There will always be some losses, power going where
you don't want it to, etc... believe me, many phd's have made their life
studies of reducing that last little bit of radiation off the side or back,
and the conclusion is??? you can't do it. there are many volumes on how to
reduce it in different cases, lots of spectacular designs that are totally
impractical for ham use, and some super applications of standard techniques
for things like the deep space network and radio astronomy.. but there is no
magic in a wire, no matter how you bend it or where you stick it.

Yagi efficiency
 

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..

Yagi efficiency
 

"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

Yagi efficiency
 

art wrote:
Even Cecil who I suggest with his extra deep physics
education gets mocked sometimes ...

Art, I'm flattered but it is wrong. I have a B.S.
degree in EE from Texas A&M and Masters work in
education from Sam Houston State. I took Balanis'
antenna course at ASU and he and I worked together
on GSM simulations because my real field of expertise
is digital electronics. What I am mocked for is
thinking outside the box, e.g. that the distributed
network model allows RF energy to be tracked through
an antenna system.
--
73, Cecil http://www.w5dxp.com

Yagi efficiency
 

John Smith wrote:
Cecil Moore wrote:
Actually Art, adding reactance reduces the current in
the element thus *decreasing* losses below what a resonant
passive element would have. Pure reactance is lossless.

On the surface, this is all very correct, however, you cannot induce
reactance without inducing some value (albeit it may, or may not, be
trivial) of pure resistance (ohmic dc), barring the use of
superconducting material, of course.

I assume you are saying that lengthening a passive
element increases the ohmic losses? Then wouldn't
shortening a passive element, to induce capacitive
reactance, decrease the ohmic losses? And in either
case, since reactance reduces the induced current
and since ohmic losses are proportional to the square
of the current while only being proportional to the
first power of resistance, wouldn't that still
decrease ohmic losses?

Can people who live by the trivial sword, also
trip and fall on that same trivial sword? :-)
--
73, Cecil http://www.w5dxp.com

Yagi efficiency
 

Dave wrote:
Cecil Moore wrote:

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

Not if the question is: What is beam efficiency? :-)

ABSOLUTELY NOT!!!!

From "Antennas For All Applications", 3rd edition by
John D. Kraus and Ronald J. Marhefka, page 665:

"Turning now to the *beam efficiency E(m)*, or the
ratio of the solid angle of the main beam Omega(m)
to the total beam solid angle Omega(a), we have ..."

All emphasis is the book author's, not w5dxp's.

From "Antenna Theory, Analysis and Design", 2nd edition,
by Constantin A. Balanis, page 63:

begin quote:
2.10 BEAM EFFICIENCY

Another parameter that is frequently used to judge the
quality of transmitting and receiving antennas is the
*beam efficiency*. For an antenna with its major lobe
directed along the z-axis (Theta = 0), as shown in
Figure 2.4(a), the beam efficiency (BE) is defined by

power transmitted(received) within cone angle Theta(1)
BE = ------------------------------------------------------
power transmitted(received) by the antenna

end quote:

In trying to figure out what definition Art is using,
this definition seems to me to be the closest.
--
73, Cecil http://www.w5dxp.com