Well this is where I am comming from, I am presently building an
antenna for this winter where I will be communicating with the U.K.
Thus my major lobe needs to be robust between about 10 degtrees and 4
degrees to ensnare most of the communication. Notwithstanding that the
upper half of the major lobe serves no usefull purpose to what the
antenna is required for there is a mass of radiation in many directions
and levels that have no connection to the required purpose of the
antenna, thus we have a lot of wasted radiation that if we harness it
so that it is used for the antennas primary use the efficiency of the
antenna would increase immensly. So to the question, accepting that the
major lobe is required in its entirety for the antennas required use I
feel that less than 50% of available radiation is used for the antennas
design usage and that also includes the upper lobe as not being a
positive contributor
However I have no real figures to hang my hat on........ O.K.?
Art

Tom Ring wrote:
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
Art


Art

Yagis, when made of almost anything but something like nichrome wire,
are very efficient. Aluminum element yagis run in the high 90's of
percent efficiency when properly designed.

My bet is that you aren't speaking of efficiency at all, but something
you don't know the words to express. Try to explain what you mean, and
this group may be able to help you.

tom
K0TAR

On 21 Sep 2006 19:09:38 -0700, "art" wrote:

Notwithstanding that the
upper half of the major lobe serves no usefull purpose to what the
antenna is required for there is a mass of radiation in many directions
and levels that have no connection to the required purpose of the
antenna, thus we have a lot of wasted radiation that if we harness it
so that it is used for the antennas primary use the efficiency of the
antenna would increase immensly.

Hi Art,

The classic solution is to stack yagis vertically. This draws down
the higher radiation lobes and puts their gain in the forward
direction.

However, unless you can positively insure that higher radiation does
not actually find its way to the target (you need a propagation
modeler to prove that, by the way), then you could be muffling
yourself at one elevation to yell at another elevation that is only
heard in points remote from the target.

In other words, if you suppress the lobe at 20 degrees to optimize the
lobe at 10 degrees, you may miss your target altogether. Given that
skip works on so many variables, an "efficient" antenna may be wholly
useless.

73's
Richard Clark, KB7QHC

Richard Clark wrote:
On 21 Sep 2006 19:09:38 -0700, "art" wrote:

Notwithstanding that the
upper half of the major lobe serves no usefull purpose to what the
antenna is required for there is a mass of radiation in many directions
and levels that have no connection to the required purpose of the
antenna, thus we have a lot of wasted radiation that if we harness it
so that it is used for the antennas primary use the efficiency of the
antenna would increase immensly.

Hi Art,

The classic solution is to stack yagis vertically. This draws down
the higher radiation lobes and puts their gain in the forward
direction.

Well you are getting closer to the question at hand. You have now
doubled the
power input but only slightly gained directionality(2db) efficiency I
would also suspect that you have flattened the lower lobe only into a
pancake shape. But again I go back to the desirable radiation which can
be said in this case to be the lower half of the major lobes half power
envelope which for a directional radiated array is very small compared
to the total radiated field.True propagation can play games but the
ARRL
give the average arrival angles over a 11 year period so it is not a
hopeless task to get a ball park figure regarding usefull radiation
knowing where the target is
I suppose I could make a model and slice out the half power lobe
portion and compare the two volumes for myself, I just thought that it
had already been looked at
Oh well back to the drawing board
Art



However, unless you can positively insure that higher radiation does
not actually find its way to the target (you need a propagation
modeler to prove that, by the way), then you could be muffling
yourself at one elevation to yell at another elevation that is only
heard in points remote from the target.

In other words, if you suppress the lobe at 20 degrees to optimize the
lobe at 10 degrees, you may miss your target altogether. Given that
skip works on so many variables, an "efficient" antenna may be wholly
useless.

73's
Richard Clark, KB7QHC

On 21 Sep 2006 20:16:31 -0700, "art" wrote:

give the average arrival angles over a 11 year period so it is not a
hopeless task to get a ball park figure regarding usefull radiation
knowing where the target is

Hi Art,

It is instructive for others to consider, so I shall proceed with very
few of those variables considered (we can see you offer nothing in the
way of time of year, time of day, frequency, Sun spot count, and so
on):

20M 0000 UT Spring 5-7 deg

20M 0000 UT Summer 4 deg

20M 0000 UT Fall 6-8 deg

20M 0000 UT Winter 7 deg

20M 1200 UT Spring 3 deg

20M 1200 UT Summer 2-10 deg (depending)

20M 1200 UT Fall 2-3 deg

20M 1200 UT Winter 4-6 deg

40M 0000 UT Spring 10 deg

40M 0000 UT Summer 8-12 deg

40M 0000 UT Fall 3-12 deg (depending)

40M 0000 UT Winter 3 deg

The numbers above say absolutely nothing about the probability of
making a contact.

If you stacked 4 to 8 yagis as high as 4 wavelengths, you might find
something "efficient."

73's
Richard Clark, KB7QHC

I'm not sure I understand the question, but a large fraction of the
total power is typically in the main lobe of a Yagi. You won't increase
the power in the main lobe significantly by reducing or eliminating
other lobes, because there just isn't much power there. If you want more
power in a narrower range of directions, you need more directionality,
which means a longer Yagi, stacked Yagis, or some other type of antenna
which will probably be larger. The methodology for and tradeoffs
involved in increasing directionality are well known. And because Yagis
(ones not having lossy traps or loading components) are very efficient,
directionality and gain are inextricably linked.

Roy Lewallen, W7EL

Roy Lewallen wrote:
I'm not sure I understand the question, but a large fraction of the
total power is typically in the main lobe of a Yagi. You won't increase
the power in the main lobe significantly by reducing or eliminating
other lobes, because there just isn't much power there.

Roy you know better than that ! gain is a binomial function with
respect
to the forward radiation at the point of initiation. It does nothing to
salvalge energy
expended in the reaward direction, to do that another vector is
required that cannot be produced by a planar array. As far as traps
being lossy as if they get hot or something that is also untrue, what
you are seeing is a radiation field created by the trap that is in
opposition to that created on the element i.e. a field that is 180
degrees out of phase



If you want more
power in a narrower range of directions, you need more directionality,
which means a longer Yagi, stacked Yagis, or some other type of antenna
which will probably be larger. The methodology for and tradeoffs
involved in increasing directionality are well known.

And because Yagis
(ones not having lossy traps or loading components) are very efficient,
directionality and gain are inextricably linked. Again I do not agree that Yagis are efficient

Art

Roy Lewallen, W7EL

art wrote:
Roy Lewallen wrote:
I'm not sure I understand the question, but a large fraction of the
total power is typically in the main lobe of a Yagi. You won't increase
the power in the main lobe significantly by reducing or eliminating
other lobes, because there just isn't much power there.

Roy you know better than that ! gain is a binomial function with
respect
to the forward radiation at the point of initiation. It does nothing to
salvalge energy
expended in the reaward direction, to do that another vector is
required that cannot be produced by a planar array.

Sorry, I can't make the slightest amount of sense out of this.

As far as traps
being lossy as if they get hot or something that is also untrue, what
you are seeing is a radiation field created by the trap that is in
opposition to that created on the element i.e. a field that is 180
degrees out of phase

Egad. There's no point in my wasting time by attempting to contribute
further to this. I'll leave you to your alternate reality.

Roy Lewallen, W7EL

Roy Lewallen wrote:
Egad. There's no point in my wasting time by attempting to contribute
further to this. I'll leave you to your alternate reality.

Now you know how I felt after your posting questioning
(denying?) the existence of reflected energy.
--
73, Cecil http://www.w5dxp.com

On Fri, 22 Sep 2006 13:21:47 -0700, Roy Lewallen
wrote:


Egad. There's no point in my wasting time by attempting to contribute
further to this. I'll leave you to your alternate reality.

Roy, it was obviously a troll, and many of us have been caught
(again).

Art's lead in "one can see that the yagi is very inefficient" should
have been recognised by us all as bait.

Owen
--

"art" wrote in message
ups.com...

Richard Clark wrote:
On 21 Sep 2006 19:09:38 -0700, "art" wrote:

Notwithstanding that the
upper half of the major lobe serves no usefull purpose to what the
antenna is required for there is a mass of radiation in many directions
and levels that have no connection to the required purpose of the
antenna, thus we have a lot of wasted radiation that if we harness it
so that it is used for the antennas primary use the efficiency of the
antenna would increase immensly.

Hi Art,

The classic solution is to stack yagis vertically. This draws down
the higher radiation lobes and puts their gain in the forward
direction.

Well you are getting closer to the question at hand. You have now
doubled the
power input but only slightly gained directionality(2db) efficiency I
would also suspect that you have flattened the lower lobe only into a
pancake shape. But again I go back to the desirable radiation which can
be said in this case to be the lower half of the major lobes half power
envelope which for a directional radiated array is very small compared
to the total radiated field.True propagation can play games but the
ARRL
give the average arrival angles over a 11 year period so it is not a
hopeless task to get a ball park figure regarding usefull radiation
knowing where the target is
I suppose I could make a model and slice out the half power lobe
portion and compare the two volumes for myself, I just thought that it
had already been looked at
Oh well back to the drawing board
Art

what you are missing is the variability in that arrival angle. if you are
interested in a specific path you must be able to receive all the possible
arrival angles, which with yagi's requires mounting several of them at
different heights. for instance consider a path from w1 to western europe
at the sunspot peak on 10m... it is not uncommon for the band to open at a
very low angle, say where a single yagi at 120' is the best antenna, then as
the day progresses the angle increases so much that the 120' antenna is
almost worthless but one at only 30' is working great. if you put
everything into getting that 10-12 degree angle you lose out by mid morning
when the arrival angle is up to 30 degrees or more... but at the same time
that top antenna may be working great into siberia!

what you are looking for is not normally called 'efficiency', but
'directivity'. unfortunately horizontally polarized yagi's vertical
radiation pattern is very dependent on height and the terrain so increasing
the directivity is seen mostly in the width of the pattern. and as noted
above, controlling the vertical pattern is normally done by changing the
antenna height, usually by stacking multiple antennas on the tower and
selecting them one at a time or in combinations to give the desired vertical
coverage. There have been some experiments with variable phasing of stacked
yagis, but it is not a common capability in amateur installations.