wrote in message
news:x_Ycd.281755$3l3.162866@attbi_s03...
What brought this to my attention was Moxon who advocated 2 element beams
(lightnes translates to greater heights) so I modeled a 20 meter beam on a 7
foot
boom and obtained 12dbi max for the band (ala 2:1)

Hi Art,

Can we assume this gain was calculated
at a particular height over ground?
Personally, I prefer FS results, in order to
eliminate any ambiguity.

but one can get 13dbi
if you drop the impedance from 50 to 12 ohms.
This then raised the question would a transformer cancel the increased
gain.

Optimizing an antenna for a specific Z
is not a good idea in my opinion, as
the amplitude of an element's current is
proportional to the amplitude of its
radiation. Ohms law tells us that at a
consistant power level, the lower the R
(Z), the greater will be the current.

A zero loss transformer would not
reduce the element's current, as the
energy being introduced to the element
would remain unchanged.

73 de Chuck, WA7RAI

"Chuck" wrote in message
news:n5gdd.8202$6P5.3752@okepread02...

wrote in message
news:x_Ycd.281755$3l3.162866@attbi_s03...
What brought this to my attention was Moxon who advocated 2 element
beams
(lightnes translates to greater heights) so I modeled a 20 meter beam on
a 7
foot
boom and obtained 12dbi max for the band (ala 2:1)

Hi Art,

Can we assume this gain was calculated
at a particular height over ground?
But ofcourse a perfect ground and a standard wavelength height

Personally, I prefer FS results, in order to
eliminate any ambiguity.
Field strength (F.S.) introduces ambiguity does it not?


but one can get 13dbi
if you drop the impedance from 50 to 12 ohms.

This paraphrases the spesific example that I gave

the question would a transformer cancel the increased
gain.
Again you paraphased the spoecific sample that I gave
which raised the same question I gave regarding transformer losses

Optimizing an antenna for a specific Z
is not a good idea in my opinion, as
the amplitude of an element's current is
proportional to the amplitude of its
radiation. Ohms law tells us that at a
consistant power level, the lower the R
(Z), the greater will be the current.

Yes there are many laws to remember and I
look at critical coupling as something to remember.



A zero loss transformer would not
reduce the element's current, as the
energy being introduced to the element
would remain unchanged.

Very true but what element would this max energy be applied to?
Via critical coupling the driven element may not be the one carrying
the maximum current and thus screws up conventional thinking.
Energy is one thing but it is current that controls radiation is it not ?.
The particular model I was working on used 50 segments per wavelength
and used element length and diameters determined by my program input .
Thus coupling gains are attained but where it sometimes determined a
element diameter
is so thin it is incapable of carrying the required current.
If I saw a vendor advertise an antenna at 13dbi I would be very suspicious
as it not the norm,
yet very realiseable when using NEC without being tied down to existing
doctrines.
Sooooooo ..... I was looking for a datum curve generated by experts from
an all encompasing
NEC program where the final design reflected the real world design without
ambiguities
regarding coupling to coils, elements e.t.c. where lumped loads do not
reflect the real
world appearance.
There have been many responses including one suggestion that a suitable
datum curve could
be formulated from customer claims no less but NONE that responds to my
specific request .
Thus a conundrum still exists regarding programs based on scientific
knoweledge that are held in question
as they do not match real world measurements that spawn most of the
villifying in this group.
Seems like a datum curve could be used as a basis for many discusions where
differences do occur
instead of just arguing for eight years or more and not resolving the
accuracy concerns
Seems like I have come full circle and describing the Presidential debates !
Art

73 de Chuck, WA7RAI

On Wed, 20 Oct 2004 00:21:10 GMT, "
wrote:
datum curve

Hi Art,

No such thing. It takes data (plural) to make a curve. Datum
(singular) is a point (i.e. NOT a curve).

If you don't see the curve you are looking for, you have an NEC
engine, what is preventing you from using it to make one, or two, or
several?

73's
Richard Clark, KB7QHC

wrote in message
news:Wbidd.156718$He1.38391@attbi_s01...

"Chuck" wrote in message
news:n5gdd.8202$6P5.3752@okepread02...


wrote in message
news:x_Ycd.281755$3l3.162866@attbi_s03...
What brought this to my attention was Moxon who advocated 2
element
beams
(lightnes translates to greater heights) so I modeled a 20
meter beam on
a 7
foot
boom and obtained 12dbi max for the band (ala 2:1)

Hi Art,

Can we assume this gain was calculated
at a particular height over ground?
But ofcourse a perfect ground and a standard wavelength height

Personally, I prefer FS results, in order to
eliminate any ambiguity.
Field strength (F.S.) introduces ambiguity does it not?

Hi Art,

FS = free space

Modeling in FS, using dBd as a reference
eliminates ambiguity.

All grounds are not equal. Including ground
effects in antenna type models that are not
ground dependant, does not reflect the
'real' world, IMO.


but one can get 13dbi
if you drop the impedance from 50 to 12 ohms.

This paraphrases the spesific example that I gave

the question would a transformer cancel the increased
gain.
Again you paraphased the spoecific sample that I gave
which raised the same question I gave regarding transformer
losses

Optimizing an antenna for a specific Z
is not a good idea in my opinion, as
the amplitude of an element's current is
proportional to the amplitude of its
radiation. Ohms law tells us that at a
consistent power level, the lower the R
(Z), the greater will be the current.

Yes there are many laws to remember and I
look at critical coupling as something to remember.

Critical coupling is simply a means to
attain element currents of a higher
amplitude than what can be expected
when one element is excited parasitically.


A zero loss transformer would not
reduce the element's current, as the
energy being introduced to the element
would remain unchanged.

Very true but what element would this max energy be applied to?

Max Energy?

I was referring to the element the transformer is
attached to.

Via critical coupling the driven element may not be the one
carrying
the maximum current and thus screws up conventional thinking.

Ummmm...

Critical coupling is a state where currents
of equal amplitude flow in two inductors that
are in close proximity, as a direct result of
the coupling. Critical coupling results in a
common field as well. This also applies to
wires (elements).

Energy is one thing but it is current that controls radiation
is it not ?.

Yes, and that's what I had said previously.

The particular model I was working on used 50 segments per
wavelength
and used element length and diameters determined by my program
input .
Thus coupling gains are attained but where it sometimes
determined a
element diameter
is so thin it is incapable of carrying the required current.

I'm not sure if I follow this correctly...
please elaborate further.

If I saw a vendor advertise an antenna at 13dbi I would be very
suspicious
as it not the norm,
yet very realiseable when using NEC without being tied down to
existing
doctrines.
Sooooooo ..... I was looking for a datum curve generated by

(data - plural)...

experts from
an all encompasing
NEC program where the final design reflected the real world
design without
ambiguities
regarding coupling to coils, elements e.t.c. where lumped loads
do not
reflect the real
world appearance.
There have been many responses including one suggestion that a
suitable
datum curve could
be formulated from customer claims no less but NONE that
responds to my
specific request .
Thus a conundrum still exists regarding programs based on
scientific
knoweledge that are held in question
as they do not match real world measurements that spawn most of
the
villifying in this group.

I suspect there can be many examples
where this occurs, but not necessarily all
are the fault of software. However, we
both know from experience, software can
be problematic in this regard.

Seems like a datum curve could be used as a basis for many
discusions where
differences do occur
instead of just arguing for eight years or more and not
resolving the
accuracy concerns

.... but when one fails to include certain
salient functions in their software - software
that is the basis for such arguments, there
is no way the arguments can be resolved
simply because there is no guarantee that
the software will be consistent with
empirical data in all cases, despite a high
order of hubris to the contrary.

Seems like I have come full circle and describing the
Presidential debates !
Art

Indeed...

73 de Chuck, WA7RAI

Ian White, G3SEK wrote:
"Drawing gain curves is a fun activity...but don`t try to read too much
into them."

I searched on "yagi boom". I got many responses. One showed Ian as the
custodian of a computer program to design yagis. Another was from the
Central States VHF Society and gives results of their 2004 gain
comparisons of many different antennas. Gain of these versus boom length
looks very ragged.

Best regards, Richard Harrison, KB5WZI

Another was from the
Central States VHF Society and gives results of their 2004 gain
comparisons of many different antennas. Gain of these versus boom length
looks very ragged.

Best regards, Richard Harrison, KB5WZI



Gain vs. boom length makes sense only when comparing or tracking the same
antenna design i.e. Yagi with multiple elements. One can design lousy antenna
on a long boom.

Jim Lawson, W2PV was one who after some modeling showed that gain in the
properly designed antenna is roughly proportional to the boom length rather
than to number of elements. Some manufacturers "beefed up" their antennas by
sticking more elements on the same boom claiming better performance.

Yuri, K3BU.us

Yes but I believe that the early computorisationd he used was based first on
mechenical designed elements which were then imputted.He did not mess with
the element diameters after that.As an aside if you densly populated a boom
with elements many are put off by the low impedance being totaslly unaware
that an additional reflector an up the input impedance back again......
another example of what coupling can do for antennas
Art
"Yuri Blanarovich" wrote in message
...
Another was from the
Central States VHF Society and gives results of their 2004 gain
comparisons of many different antennas. Gain of these versus boom length
looks very ragged.

Best regards, Richard Harrison, KB5WZI



Gain vs. boom length makes sense only when comparing or tracking the same
antenna design i.e. Yagi with multiple elements. One can design lousy
antenna
on a long boom.

Jim Lawson, W2PV was one who after some modeling showed that gain in the
properly designed antenna is roughly proportional to the boom length
rather
than to number of elements. Some manufacturers "beefed up" their antennas
by
sticking more elements on the same boom claiming better performance.

Yuri, K3BU.us

In any case the curve was normalized across several factors and was to be used
as a guideline to substantiate that the longer the boom the higher the gain.
Other factors like F/B, F/S, bandwidth, losses, etc. were not addressed.

wrote:

My ARRL books go back a decade or more
and the graph showing gain per boom length
has several curves based on different measurements
e.t.c. Has a graph been made based solely on NEC
program findings over say a perfect ground and at a uniform height?
Art



For VHF/UHF yagis in free space -

WA2PHW Gain Figure of Merit

G = 10 log (5.4075 B + 4.25) for B GT 1

Where G is gain in dBd and B is boomlength in wavelengths.

This is from a database of over 100 VHF/UHF yagis compiled in the early
90's. These are all real buildable yagis, and the antenna range numbers
closely agree with the computer models. The numbers were heavily
influenced by the 10 to 40 element K1FO series. Thanks again Steve.

Note that this predicts a zero length yagi should have about 6 dBd gain.
Any ideas on why it intercepts there?

tom
K0TAR

Tom, where is the link that goes with this info? It doesn't mean anything as
it stands
Art


wrote in message
. ..
wrote:

My ARRL books go back a decade or more
and the graph showing gain per boom length
has several curves based on different measurements
e.t.c. Has a graph been made based solely on NEC
program findings over say a perfect ground and at a uniform height?
Art



For VHF/UHF yagis in free space -

WA2PHW Gain Figure of Merit

G = 10 log (5.4075 B + 4.25) for B GT 1

Where G is gain in dBd and B is boomlength in wavelengths.

This is from a database of over 100 VHF/UHF yagis compiled in the early
90's. These are all real buildable yagis, and the antenna range numbers
closely agree with the computer models. The numbers were heavily
influenced by the 10 to 40 element K1FO series. Thanks again Steve.

Note that this predicts a zero length yagi should have about 6 dBd gain.
Any ideas on why it intercepts there?

tom
K0TAR