" wrote in message
news:xOzcd.263953$D%.243703@attbi_s51...
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


They probably have been done but there will not be much difference between
them and the ARRL graphs. Its been long known how to calculate antenna gain,
computers just take the teadous labor out of it.

Jimmy,
I did not want to choose a curve that matches my modelling which you can
when presented with three different curves all of which are formulated at
different
times by different people. I would have thought that the advent of NEC
would
render these curves redundant !
Art

"Jimmie" wrote in message
. com...

" wrote in
message
news:xOzcd.263953$D%.243703@attbi_s51...
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


They probably have been done but there will not be much difference between
them and the ARRL graphs. Its been long known how to calculate antenna
gain,
computers just take the teadous labor out of it.

Art Unwin wrote:
"Has a graph been made based solely on NEC program findings over say a
perfect ground and at a uniform height?"

I don`t know, but I`ve seen Yagi-Uda gain versus boomlength charts.

Before relying on such charts, it may be worthwhile to read "The
Yagi-Uda Story" on page 246 of the 3rd edition of Kraus` "Antennas".

Also, the solution to a Deutsche Welle Short Wave Antenna problem on
page 703 is given on page 705:

"the gain of a single 1/2-wave dipole is 2.15 dBi and of 2 collinear
in=phase 1/2-wave dipoles is 3.8 dBi. The array of 8 such collinear
dipoles adds 3+3+3=9 dB. The reflector screen adds 3 more and the ground
bounce another 6 dB for a total gain of 3.8+9+3+6=21.8 dBi or a
directivity of 151 approx."

The solved problem is worth the price of the book as a reality check.

Best regards, Richard Harrison, KB5WZI

"Richard Harrison" wrote in message
...
Art Unwin wrote:
"Has a graph been made based solely on NEC program findings over say a
perfect ground and at a uniform height?"

I don`t know,

Neither do I thus the question

but I`ve seen Yagi-Uda gain versus boomlength charts.

So have I but not based on NEC


Before relying on such charts, it may be worthwhile to read "The
Yagi-Uda Story" on page 246 of the 3rd edition of Kraus` "Antennas".

Also, the solution to a Deutsche Welle Short Wave Antenna problem on
page 703 is given on page 705:

"the gain of a single 1/2-wave dipole is 2.15 dBi and of 2 collinear
in=phase 1/2-wave dipoles is 3.8 dBi. The array of 8 such collinear
dipoles adds 3+3+3=9 dB. The reflector screen adds 3 more and the ground
bounce another 6 dB for a total gain of 3.8+9+3+6=21.8 dBi or a
directivity of 151 approx."

The above extract is lost on me as I was looking for maximum gain per unit
boom length based on NEC without regard to number of elements
required to attain that gain. Thus increases or decreases from critical
coupling
can be ascertained..

Art


The solved problem is worth the price of the book as a reality check.

Best regards, Richard Harrison, KB5WZI

wrote:

The above extract is lost on me as I was looking for maximum gain per
unit boom length based on NEC without regard to number of elements
required to attain that gain. Thus increases or decreases from
critical
coupling
can be ascertained..

You misunderstand what this curve is telling you.

There is a general law that gain is proportional to "aperture area". For
something like a dish, "aperture area" is the frontal area of the dish
itself (multiplied by an efficiency factor 1). For long yagis,
"aperture area" is roughly proportional to boom length.

This concept has nothing whatever to do with NEC! But it is the absolute
bedrock of all antenna engineering. What you really need right now is to
read the first few chapters of Kraus... and understand these most basic
principles.

NEC calculations will not tell you anything about this. NEC is simply a
tool to calculate what the gain of a particular antenna will be (or can
be, if you build it as modeled).


--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek

wrote:
I did not want to choose a curve that matches my modelling which you
can
when presented with three different curves all of which are formulated
at different
times by different people. I would have thought that the advent of NEC
would
render these curves redundant !

The plot of many individual yagis does confirm the general idea of gain
being roughly proportional to boom length, and that is a very important
thing to understand.

Note that this is only for long-ish yagis with many elements. For yagis
of 2-3-4 elements on a short boom, the first few dB of gain come very
easily. Beyond that, the data points settle back towards the long-yagi
trend line.

To increase the gain by 3dB, you need to either double the boom length
(and redesign the yagi, obviously) or else stack two of the same
yagis... and either way, in practice you'll achieve slightly less than
3dB.


--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek

Ian, All the points you made are very good especialy when you
stated that gain is ROUGHLY proportional to boom length and
then go on to mention "aperture'
The question I asked was very specific but not personal like the
presidential
debates this newsgroup uses the question as the basis for what they want to
say.
The reason I asked the specific question was to obtain a datum line for
antennas relative to gain and a well used term of boom length.
NEC programs can provide this basic if the latest revision is used
and the program is all encombassing.( Many are not)
Mention coupling and some experts go nuts
but NEC is all encompassing provides definitive answers that remove
measurement errors presently shown and cuts through a lot of garbage.
All encompassing is all important in that sufficient segments are available
together with the use of variuable dimensions as this gets away from use of
methods
to get around inadequacy of a particular program. You mention "aperture"
but I don.t believe it changes any results given by NEC. Others ridicule the
use of the term
critical coupling yet NEC shows that element currents can be changed via
coupling
and it is current placement that we are interested in, so why so much
redicule/
The same goes for element diameters NEC provides the correct construction
for
elements which is another important variable for gain
So in other words, a NEC curve would deflect most arguments and personal
agenders
from the beginning and if one supplies actual measurement that are contrary
to those of NEC
then we have a basis for truly specific debate. As somebody pointed out, one
slanging match
has been going on for more than eight years regarding the use of critical
coupling, another is
the subject of coils, actual measurement versus a manipulated program
calculation.
I pretty much have had it with excuses regarding inadequecies of some
programs,
If NEC is a really viable tool; then let us use it as a datum by using a NEC
program that
is all encompassing to judge measured claims against so hat true specific
can be judged.
It is possible after all that even NEC may obtain several more revisions
over time because of
actual measurement which can only aid all in the understanding of antennas
and the removal
of old wifes tales and private agendas that evolved prior to NEC.
Is it auguments that we yearn for on this newsgroup or true resolution of
ideas?
Art



"Ian White, G3SEK" wrote in message
...
wrote:
I did not want to choose a curve that matches my modelling which you
can
when presented with three different curves all of which are formulated
at different
times by different people. I would have thought that the advent of NEC
would
render these curves redundant !

The plot of many individual yagis does confirm the general idea of gain
being roughly proportional to boom length, and that is a very important
thing to understand.
clip

" wrote in message
news:t4bdd.277152$D%.236528@attbi_s51...
Ian, All the points you made are very good especialy when you
stated that gain is ROUGHLY proportional to boom length and
then go on to mention "aperture'
The question I asked was very specific but not personal like the
presidential
debates this newsgroup uses the question as the basis for what they want
to
say.
The reason I asked the specific question was to obtain a datum line for
antennas relative to gain and a well used term of boom length.
NEC programs can provide this basic if the latest revision is used
and the program is all encombassing.( Many are not)
Mention coupling and some experts go nuts
but NEC is all encompassing provides definitive answers that remove
measurement errors presently shown and cuts through a lot of garbage.
All encompassing is all important in that sufficient segments are
available
together with the use of variuable dimensions as this gets away from use
of
methods
to get around inadequacy of a particular program. You mention "aperture"
but I don.t believe it changes any results given by NEC. Others ridicule
the
use of the term
critical coupling yet NEC shows that element currents can be changed via
coupling
and it is current placement that we are interested in, so why so much
redicule/
The same goes for element diameters NEC provides the correct construction
for
elements which is another important variable for gain
So in other words, a NEC curve would deflect most arguments and
personal
agenders
from the beginning and if one supplies actual measurement that are
contrary
to those of NEC
then we have a basis for truly specific debate. As somebody pointed out,
one
slanging match
has been going on for more than eight years regarding the use of critical
coupling, another is
the subject of coils, actual measurement versus a manipulated program
calculation.
I pretty much have had it with excuses regarding inadequecies of some
programs,
If NEC is a really viable tool; then let us use it as a datum by using a
NEC
program that
is all encompassing to judge measured claims against so hat true
specific
can be judged.
It is possible after all that even NEC may obtain several more revisions
over time because of
actual measurement which can only aid all in the understanding of antennas
and the removal
of old wifes tales and private agendas that evolved prior to NEC.
Is it auguments that we yearn for on this newsgroup or true resolution of
ideas?
Art



"Ian White, G3SEK" wrote in message
...
wrote:
I did not want to choose a curve that matches my modelling which you
can
when presented with three different curves all of which are formulated
at different
times by different people. I would have thought that the advent of NEC
would
render these curves redundant !

The plot of many individual yagis does confirm the general idea of gain
being roughly proportional to boom length, and that is a very important
thing to understand.
clip


There is no direct connection between boom length and gain. This is because
lengthing the boom also implies one has added elements and possibly made
adjustments to element spacing. A good source of the data you seek may be an
antenna catalog(or manufacturers web site). compare the published gains of
the different length antennas.

Jimmie wrote:
The plot of many individual yagis does confirm the general idea of gain
being roughly proportional to boom length, and that is a very important
thing to understand.
clip


There is no direct connection between boom length and gain. This is
because lengthing the boom also implies one has added elements and
possibly made adjustments to element spacing.

Sorry, I should have said that boom length is roughly proportional to
the *available* gain, if the whole length of the boom is populated with
elements in such a manner as to optimize the gain. That requirement is
usually taken as understood.


--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek

A graph from NEC data is going to be pretty much like a graph from the ARRL
books. By putting the data in a graphic form your are placing the same
limits on the data as they had to in the ARRL books. The ARRL graphs give
you a pretty good idea of what goes on when you change element spacing,
number of elements and so on. What they dont do is alllow you to perform
optimization like the NEC programs . Graphing a NEC program output would be
the same as going back to the time all you had was the graphs to go by
unless you are willing to do all the calculations on your slide rule or
calculator. What I am saying is that you already have this data. No point in
reinventing the wheel.Unless you think yiou can get a patent on it.

" wrote in message
news:65Zcd.150611$He1.116446@attbi_s01...
Jimmy,
I did not want to choose a curve that matches my modelling which you can
when presented with three different curves all of which are formulated at
different
times by different people. I would have thought that the advent of NEC
would
render these curves redundant !
Art

"Jimmie" wrote in message
. com...

" wrote in
message
news:xOzcd.263953$D%.243703@attbi_s51...
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


They probably have been done but there will not be much difference
between
them and the ARRL graphs. Its been long known how to calculate antenna
gain,
computers just take the teadous labor out of it.