Yagi efficiency
 

Remember only R is of consideration for the addition of power from each
element which provides flux unless you can quantasize reaction for me
as producing the emmision of flux other than a indication of the
direction it takes .

I assume you are talking about radiation resistance.
There are other R's that cause loss of desired radiation
including conduction-dielectric losses. Some signal
is lost to the ground after being radiated.

Assuming that your definition of efficiency includes
beam efficiency, I would suggest taking an optimized
two-element Yagi into EZNEC and determining the maximum
gain. Then replace the reflector by an element identical
to the driven element including the source signal. Using
the same amount of total driving power, if you can come
up with a gain superior to the Yagi, would that prove
the point you are trying to make?
--
73, Cecil http://www.w5dxp.com

Yagi efficiency
 

Jimmie D wrote:
The radiation IS NOT cancelled ...

Doesn't the performance of non-reflecting glass
depend upon EM wave cancellation? Doesn't the
gain of a beam depend upon EM wave cancellation
in some other direction?
--
73, Cecil http://www.w5dxp.com

Yagi efficiency
 

Dave wrote:
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".

It was more than likely an inclusive statement, not an
exclusive one. I suspect Art meant, "a reactive impedance
term value" when he said "a reactive impedance value".
--
73, Cecil http://www.w5dxp.com

Yagi efficiency
 

"Cecil Moore" wrote in message
.. .
Jimmie D wrote:
The radiation IS NOT cancelled ...

Doesn't the performance of non-reflecting glass
depend upon EM wave cancellation? Doesn't the
gain of a beam depend upon EM wave cancellation
in some other direction?
--
73, Cecil http://www.w5dxp.com

The radiation is not cancelled in the way ART means, One of the problems of
replying to his post is you can not do really do it without sounding like an
idiot.

Yagi efficiency
 

Doesn't the performance of non-reflecting glass
depend upon EM wave cancellation?
This I can respond to (though I doubt that I should)

The term usually used is "anti-reflective" and refers to a specific
multi-coating technique on the glass (or other medium).

the "anti" refers to destructive wave interference for reflected light
by varying the refractive index of successive coatings. Thus, MORE of
the incident travels through the medium than is reflected back

If the goal is to increase the % of light refracted THROUGH the medium,
then anti-reflective coating increases the efficiency.

Take the same glass without the AR coating, and LESS light is refracting
THROUGH the medium (more reflecting back): lower efficiency.

This definition of efficiency only makes sense when you're interested in
light refracted through the glass.

P-in / P-out does not = this definition of efficiency.

The efficiency definition implies interest in directionality.

Is this not where the confusion lies in all these posts?

John

PS,
Think of a simple flashlight with a mirror and a lens.

As a simple analogy, the filament of the light is the driven element
with a mirror behind and a lens in front...a LIGHT Yagi, no?

No diff in P-in/p-out...just all light directed out of the flashlight
into a beam.

Yagi efficiency
 

Cecil Moore wrote:
art wrote:
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 ...

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
Regards
Art




Seems to me that the reactance in the passive elements
provides a phase shift that causes destructive interference
in the desired places and constructive interference in
the desired places.

I came in late and thus apologize if anyone else has stated
this earlier.
--
73, Cecil http://www.w5dxp.com

Yagi efficiency
 

Cecil Moore wrote:
art wrote:
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 ...

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
Regards
Art




Seems to me that the reactance in the passive elements
provides a phase shift that causes destructive interference
in the desired places and constructive interference in
the desired places.

I came in late and thus apologize if anyone else has stated
this earlier.
--
73, Cecil http://www.w5dxp.com

Yagi efficiency
 

PS,
Think of a simple flashlight with a mirror and a lens.

As a simple analogy, the filament of the light is the driven element
with a mirror behind and a lens in front...a LIGHT Yagi, no?

No diff in P-in/p-out...just all light directed out of the flashlight
into a beam.

John,

You're right about the efficiency, but be careful with the flashlight
analogy. A light yagi might have ~ 200 nanometer long elements.

An 20m band reflector analogous to that in a mini maglight would have
to be 800 miles in diameter.

The analogy with respect to efficiency is fine... but there's no HF
antenna that can form a beam like that.

73,
Dan

Yagi efficiency
 

Interesting Jimmy
Could you show me how me how a vector directed at a socalled reflector
behaves with respect to a constant plane without the implication of a
neutralising effect.
Now the reflector "works" only as a part of a particular plane so
please go on from there.
I often read of additive and subtractive radiation in books written by
the masters and I have seemed to have got the wrong idea about these
matters
Art

Jimmie D wrote:
"art" wrote in message
oups.com...
From a theoretical way of getting at the answer it seems
a logical way of proceding. So now to the rest of the task.1 how do we
determine volumes that you talk about that are a result of deflection 2
How do we determine
radiation that was cancelled or neutralised and 3 How do you determine
the radiation volume created by ground reflection so we can work back
to search for ground losses. That last one really bothers me as I have
never got a good handle on the contribution of ground reflection to any
particular part of the radiation envelope.

Art



Denny wrote:
For those who wish to actually learn and not just insult each other,
get a calculator, learn how to calculate Cosine Theta a trivial math
problem that any 9th grader can be taught in 5 minutes flat, get a BIG
piece of paper reason to come, and actually calculate the shape and
vector length of the lobes of a two element Yagi-Uda antenna... Do the
calculation in both the horizonal and vertical planes... From that you
can calculate the volume of each lobe, which is proportional to the
percentage of power in each lobe... From that number you can very
simply calculate what percentage went into the lobes you prefer and
what went in the lobes you don't prefer...

Now, the reason for the BIG piece of paper... The antenna patterns you
see on the screen with EZNEC, or in the antenna handbooks, are
logarithmic, not linear and there are flavors to them, ARRL, linear
logarithmic, modified logarithmic... So, the patterns are
distorted... Why is that? Because if they were linear and the front
lobe and the rear lobe are to the same scale the front lobe will take
up the entire length of the screen/paper and the rear lobe will need a
magnifying glass to be seen... A rear lobe that is 20dB down from the
front lobe is down by the power ratio of 100... So, if your forward
lobe calculates out to be 10 inches long, the rear lobe will be be 1/10
of an inch.... I'll let you figure out the size of a lobe that is 30dB
down (get out your microscope)

For those who want to review do a search on Joseph Reisert, who has
published numerous writings on antennas and patterns... There many are
others also, but Joe is published on the web, and very readable...

cheers ... denny / k8do

The radiation IS NOT cancelled or Neutralized. You need to learn more about
what is going on with an antenna. I suggest you do some serious reading,
actually reading with an open mind and not reading trying to find little
phrases that seem to you to prove your beliefs. It should be fairly obvious
that if an antenna worked by neutralization or cancelation that it would
take more energy to cancel out radiation in the undesired direction of a
yagi than is available in the desired direction. Therefore a Yagi or any
other antenna does not work by cancellation.

I gues I could express this a lot better but its late and whats the use.

Yagi efficiency
 

Cecil Moore wrote:
Remember only R is of consideration for the addition of power from each
element which provides flux unless you can quantasize reaction for me
as producing the emmision of flux other than a indication of the
direction it takes .

I agree there are other losses but to prevent including losses that are
outside the E and H process change over such as ground reflections etc
is it not better to just accept The pure resistance only so there is no
need to characterize individual losses Once you go beyond the near
field it gets complicated as losses are created outside the EH
generation process.
Ii am not sure how the EZNEC thing functions but if you design the
array where all elements are driven you can then use the individual
element impedances to determine overall efficiency.i.e. power in versus
power out
Fortunately thats the way my program can operate
Art


I assume you are talking about radiation resistance.
There are other R's that cause loss of desired radiation
including conduction-dielectric losses. Some signal
is lost to the ground after being radiated.

snipe?
--
73, Cecil http://www.w5dxp.com