Yagi efficiency
 

Cecil Moore wrote:
John Smith wrote:
Cecil Moore wrote:

Can people who live by the trivial sword, also
trip and fall on that same trivial sword? :-)

Cecil:

Yes they can. And, that would be no trivial trip! It is just, in the
dark, like I am most of the time, I can't seem to avoid them, the trips.

However, what I am saying can be proved, or disproved in the real world.
What I am saying, is construct a SHF antenna and chuck a xmitter and
pa behind it. Encase the antenna in good insulating (polyurethane foam
for instance?) material and have a temperature sensor attached to each
element. Crank up the power and you will see some sort of rise in temp
in the director (indeed, it should be seen in ALL elements), since heat
= loss (actually, since we all accept the law of conservation of energy,
loss is a misnomer, really it is only a change in frequency, from rf to
infrared--beware a trivial trip!) we demonstrate an induced loss in the
system.

Next, remove all elements and materials to a distance from the de where
absolutely no coupling can occur. Tune and match the de to the pa
output, now bring the director into proximity to the de, observe the
power flow to the de as you finally set the director into proper
position to form a good frontal lobe, you MUST now re-tune and adjust
the de, this is because electrical factors (resistance, reactance and
possible other factors we are not even aware of) of the director are now
being "mirrored" into the de (an ohmic loss (heat) should also have
risen in the de due to the mirrored directors imperfections.)

That is all I am saying. Now we would have go get out our equipment
which can measure the weight of fly wings to know the real importance of
all that...

Geesh Cecil, you never ask ANY simple questions!

Warmest regards,
JS

Yagi efficiency
 

Jimmie D wrote:
The radiation is not cancelled in the way ART means.

Sorry, I came in late. Here's a quotation from a web
site concerning wave cancellation that might help:

"... when two waves of equal amplitude and wavelength
that are 180-degrees ... out of phase with each other
meet, they are not actually annihilated, ... All of the
photon energy present in these waves must somehow be
recovered or redistributed in a new direction, according
to the law of energy conservation ... Instead, upon
meeting, the photons are redistributed to regions that
permit constructive interference, so the effect should
be considered as a redistribution of light waves and
photon energy rather than the spontaneous construction
or destruction of light."

If the EM energy doesn't change form, the destructive
interference from wave cancellation must result in
an equal magnitude of constructive interference
somewhere else - like squeezing a balloon. Sorry if
this has been said previously.
--
73, Cecil http://www.w5dxp.com

Yagi efficiency
 

art 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.

This current that you are referring to, I used P =I squared R
which leads to lower power. Where did I go wrong

Lower power results in lowering the loss due to heat.
That leaves more power available to be radiated by
the antenna system but not necessarily radiated by
this single element that we are discussing. I suspect
two driven elements are theoretically capable of
better performance than a two element Yagi given
equal total power input into the elements.
--
73, Cecil http://www.w5dxp.com

Yagi efficiency
 

Yagi efficiency
 

IIf you can design a bandpass filter in a RLC or complex circuitry
method then you can design an antenna array that does the same thing.
That is not out of the box thinking.Just remove coupling from the
overall function

Regards
Art
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
 

Exactly.That is similar to two equal forces acting to compressa piece
of steel Opposite to when you use tension the side forces press inwards
until a 45 degree break or shear angle occurs where the vectors forces
move out at right angles to the compressive force Newton is correct,
you cant destroy energy
Art:
Jimmie D wrote:
The radiation is not cancelled in the way ART means.

Sorry, I came in late. Here's a quotation from a web
site concerning wave cancellation that might help:

"... when two waves of equal amplitude and wavelength
that are 180-degrees ... out of phase with each other
meet, they are not actually annihilated, ... All of the
photon energy present in these waves must somehow be
recovered or redistributed in a new direction, according
to the law of energy conservation ... Instead, upon
meeting, the photons are redistributed to regions that
permit constructive interference, so the effect should
be considered as a redistribution of light waves and
photon energy rather than the spontaneous construction
or destruction of light."

If the EM energy doesn't change form, the destructive
interference from wave cancellation must result in
an equal magnitude of constructive interference
somewhere else - like squeezing a balloon. Sorry if
this has been said previously.
--
73, Cecil http://www.w5dxp.com

Yagi efficiency
 

Cecil Moore wrote:
art 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.
Whoa Cecil i dont follow that at all
art





This current that you are referring to, I used P =I squared R
which leads to lower power. Where did I go wrong

Lower power results in lowering the loss due to heat.
That leaves more power available to be radiated by
the antenna system but not necessarily radiated by
this single element that we are discussing. I suspect
two driven elements are theoretically capable of
better performance than a two element Yagi given
equal total power input into the elements.
--
73, Cecil http://www.w5dxp.com

Yagi efficiency
 

More current is not necessarily used for reradiation .
You also have circulating current because of inherrant
inductance and capacitance since we are dealing with a series
circuit. You can add resistance to the circuit when you are at
some distance from resonance which is similar to forming band
pass shapes but the bottom line is that at resonance or near
resonance pure resistance rules To get closer to what is really
happening is to go back to 455 khz when used in radio
circuits to revive the memory
Art


Cecil Moore wrote:
art 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.

This current that you are referring to, I used P =I squared R
which leads to lower power. Where did I go wrong

Lower power results in lowering the loss due to heat.
That leaves more power available to be radiated by
the antenna system but not necessarily radiated by
this single element that we are discussing. I suspect
two driven elements are theoretically capable of
better performance than a two element Yagi given
equal total power input into the elements.
--
73, Cecil http://www.w5dxp.com

Yagi efficiency
 

Tom Ring wrote:
art wrote:

Not a reasonable answer, could be speculation like some of the comments
I get from experts. The yagi is not totally efficient in changing the
time changing field to a radiative field
because it has detuned elements contrary to what Roy states that a
reflector aids the forward lobe.......that is trash talk but many of
the so called experts are following like lemmons


So why is it then, that Roy and several dozen others here have made good
livings, written respected books, and designed antenna systems that
defined how good it can get? And all you have done is call them names?
When I don't agree with them they call me names It is always them or
their followers and I eventually retaliate with a vengance and I think
I can do it better than them.
They are of a group that everything is known about antennas and is
written in books. If you refer to something that is not in the books
then they attack where I wish they would take a bit of time trying to
understand what I am getting at so I can make use of their superior
knowledge outside of yagis but yagis dominate their whole life to the
exclusion of anything else so we are at an impasse. Tough but it is of
their choice where I have offered my hand many times only to be
rejected.
Art







Sounds like the "so called experts" are a lot effing smarter than you.

All you have done is throw stones, which is what you accuse all of us
of, by the way. And you haven't given a microgram of proof that what
you believe is true.

tom
K0TAR

Yagi efficiency
 

art 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.

Whoa Cecil i dont follow that at all

Resonant passive elements absorb more power
than do non-resonant passive elements. Resonant
passive elements therefore dissipate more heat
than non-resonant passive elements.

With EZNEC, check out the feedpoint impedance
of a two element Yagi when both elements are
resonant Vs when one element is 5% longer and
a non-resonant reflector.

The following values are not optimized by any
means but will give you an idea.

With ten foot spacing between two 33 foot elements

The gain is virtually bidirectional at 10.7 dBi.
The feedpoint impedance is 20 ohms and the current
induced in the passive element is 0.84 amps.

Keeping everything else the same and adding one
foot to the reflector yields the following results.

The gain increases to 11.9 dBi with a F/B ratio
of about 8 dB. The feedpoint impedance is 30 ohms
and the current induced in the passive element is
lower at 0.75 amps.

Making the reflector non-resonant causes its current
to fall by about 0.1 amp thus reducing losses while
the feedpoint impedance has increased by 50% and the
gain has increased by 1.2 dB. There doesn't seem to
be any downside to non-resonant passive elements.
--
73, Cecil http://www.w5dxp.com