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.