I understand where you are coming from Cecil but let me turn your
statement around. How are you going to account for these additions and
subtractions in accepted equations by the masters that produce the
legitamacy of RLC or complex circuitry equeationd if they are known as
loss less and not a lumped item around which electromechanics thrive?
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 ...True it does have directive value
as cos phi or power factor but it is a variable and not a constant
which circuitry requires.
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 . Really Cecil I am trying to get people to think
about elements containing inherranr directional properties so that
uneeded radiation is harnessesd for useful purposes but they are
shutting their ears.
Art

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.

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

"art" wrote in message
Really Cecil I am trying to get people to think
about elements containing inherranr directional properties so that
uneeded radiation is harnessesd for useful purposes but they are
shutting their ears.
__________________

Art,

The dipole elements (of all lengths) in a Yagi _do_ have their own
directional properties, and generate their own radiation patterns -- the
fields of which add/subtract in space as a function of their relative
magnitudes and phases to produce a net field that varies around the
radiation sphere centered on the antenna.

From reading between the lines, maybe you are relating antenna efficiency to
the free-space field strength that the antenna produces at a given distance
and direction in the far field when a given amount of r-f power is applied
to its input terminals, compared to the field produced for the same
conditions by a reference radiator such as a 1/2-wave dipole, or an
isotropic source.

For this definition it is reasonable to expect that both the test and the
reference antenna have negligible conductor and dielectric loss, and that
they both present a return loss of 30 dB or better to the transmission line
leading to the transmitter. All of that is practical to achieve. Also note
under these conditions that a return loss of 30 dB means that 99.9% of the
power applied to the antenna is radiated (somewhere), so if that is the
meaning of antenna efficiency, it is high indeed.

By this definition, the efficiency of a Yagi in its direction of maximum
field is very high, and does not indicate that sub-optimal choices were made
for its mechnical layout. In fact, the inventors of this antenna and many
others have spent much time and effort with physical and electrical models
of the Yagi to optimize its patterns and gains. The result of all that
finds that the director(s) should be shorter than the driven element, that
the reflector should be longer, and that using more than one reflector has
minimal effect. That is the "bottom line," and speculation to the contrary
won't change it.

Using this Yagi design and this definition of efficiency, a standard,
6-element Yagi has a main lobe peak efficiency of about 250% compared to a
1/2-wave dipole, and 316% compared to an isotropic radiator, which
correspond to radiated power ratios of about 610% and 1,000%, respectively.

IEEE Standard 145-1983 gives the standard definitions of terms for antennas
(gain, directivity, efficiency etc).

RF

"Richard Fry" wrote in message
...
"art" wrote in message
Really Cecil I am trying to get people to think
about elements containing inherranr directional properties so that
uneeded radiation is harnessesd for useful purposes but they are
shutting their ears.

every thing that radiates has 'inherent directional properties'. it is
those properties that software like nec models. adding up all the
contributions of lots of little tiny pieces of radiating current is what
goes into designing all sorts of antennas, including yagis. there is no
magic wire that is going to get more power on target, no strange property
that is going to give you super gain, and no way to get rid of all the
'uneeded radiation'. There will always be some losses, power going where
you don't want it to, etc... believe me, many phd's have made their life
studies of reducing that last little bit of radiation off the side or back,
and the conclusion is??? you can't do it. there are many volumes on how to
reduce it in different cases, lots of spectacular designs that are totally
impractical for ham use, and some super applications of standard techniques
for things like the deep space network and radio astronomy.. but there is no
magic in a wire, no matter how you bend it or where you stick it.

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

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

art wrote:


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



Does this mean you are ignoring any interaction between elements?