Cecil, efficiency depends on what your objectives are
The yagi antennas objective is to obtain a radiation beam of gain
compared
to radiation else where. What is wanted is a radiation lobe that one
can use to direct communication. ..rThe yagi achieves the object of
producing a lobe which has a higher gain than other lobes that the yagi
produces.( A higher ratio) The yagi achieves its object by producing
this
main lobe but at what cost? If we look at pattern volume as reflecting
as energy applied to the yagi we must compare that volume with the
whole pattern volume. This means comparing the volume of the upper
lobes, the side lobes, the rear lobe and of course the vertical lobe to
the main lobe. Any cursury look at a three D radiation pattern will
immediately see that the main lobe is less than 50 % of the total
radiation pattern
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 where
the addition of a reflector does nothing to enhance increased forward
radiation 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 just comparing the forward and the rear lobe we
have only achieved 50 per cent of our object
and this is not counting other losses. Now you may disagree with the
objective of a yagi beam and I understand that may be the case.
Hopefully the above answers your request to
define efficiency as I was with respect to the yagi antenna. I think
the above pretty much explains what I stated in the initial post tho it
appears that some read inbetween the lines to read what they wanted to
read as a diversionary tactic and there is not much anybody can do
about that. One really has to ask themselves the question that if an
antenna came on the market with only one main lobe would they buy it
Art.

Cecil Moore wrote:
art wrote:
When one looks at a.radiating array pattern one can see that the yagi
is very inefficient.

Please define "efficiency".
--
73, Cecil, http://www.w5dxp.com

"art" wrote in message
oups.com...
Cecil, efficiency depends on what your objectives are
The yagi antennas objective is to obtain a radiation beam of gain
compared
to radiation else where. What is wanted is a radiation lobe that one
can use to direct communication. ..rThe yagi achieves the object of
producing a lobe which has a higher gain than other lobes that the yagi
produces.( A higher ratio) The yagi achieves its object by producing
this
main lobe but at what cost? If we look at pattern volume as reflecting
as energy applied to the yagi we must compare that volume with the
whole pattern volume. This means comparing the volume of the upper
lobes, the side lobes, the rear lobe and of course the vertical lobe to
the main lobe. Any cursury look at a three D radiation pattern will
immediately see that the main lobe is less than 50 % of the total
radiation pattern
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 where
the addition of a reflector does nothing to enhance increased forward
radiation 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 just comparing the forward and the rear lobe we
have only achieved 50 per cent of our object
and this is not counting other losses. Now you may disagree with the
objective of a yagi beam and I understand that may be the case.
Hopefully the above answers your request to
define efficiency as I was with respect to the yagi antenna. I think
the above pretty much explains what I stated in the initial post tho it
appears that some read inbetween the lines to read what they wanted to
read as a diversionary tactic and there is not much anybody can do
about that. One really has to ask themselves the question that if an
antenna came on the market with only one main lobe would they buy it
Art.

Cecil Moore wrote:
art wrote:
When one looks at a.radiating array pattern one can see that the yagi
is very inefficient.

Please define "efficiency".
--
73, Cecil, http://www.w5dxp.com


There are already words defined to mean the antenna parameters you are
talking about. I suggest you use these instead of defining yur own so people
will know what you are talking about. Antenna patterns are expressed in db.
This means they are logarthmicly compressed. IF they were displayed linearly
the sidelobes would would be invisible on the graph. Again. ad nauseum,
there is no significant power in a sidelobe of any reasonably designed yagi
antenna..

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

"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

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.