Gain per unit length of boom
 

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

Hi Art,

While this was the common theory many years ago, there other ways to get
gain from an antenna other than boom length and number of elements.

ie On 2m we are able to get 11.2 dBd on a 45inch boom with 3 elements
stacked 2 wide. Yes, this is range tested see results at
http://www.csvhfs.org/ant/CSANT04.HTML


73,
Guenther VE3CVS
www.degendesigns.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

" 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.

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?

There is a table of data calculated by VE7BQH for a large number of
different yagis, at:
http://www.ifwtech.co.uk/g3sek/diy-yagi/ve7bqh.htm
(These are not calculated by NEC, but by another very adequate program.)

You can draw your own curve from the data in the L(WL) and Gain columns.
Since all the data have been calculated by the same person, starting
from the antenna's mechanical dimensions, and using the same program,
this removes a lot of variables.

You will see a broad trend of increasing gain with boom length, but
there is still a lot of scatter due to variations between different
designs. Also bear in mind that gain isn't everything, and a long yagi
that has been maximized for gain may be a poor antenna in other ways,
such as sidelobe levels, ease of pointing, sensitivity to water on the
elements, ease of matching etc.

Drawing gain curves is a fun activity... but don't try to read too much
into them.


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

On Mon, 18 Oct 2004 18:26:35 +0100, "Ian White, G3SEK"
wrote:

Drawing gain curves is a fun activity... but don't try to read too much
into them.

Hi Ian,

While at a lecture, the lecturer got a question from the audience that
was premised "don't believe everything you think."

73's
Richard Clark, KB7QHC

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.

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) 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. On the F/B
question it was of real interest to me to compare the first frontal lobe
gain to the second lobe at
the rear on the basis that propagation rules the second rear lobe as the
most important .
But all of this comes to a grinding halt if there is not a datum curve to
which one can
compare ones modeling when using more than two elements on such a short
boom..
I agree that one has to model to one's specific needs and as can be seen
from the ARRL curves
using short booms max gain varies tremendously.depending on curves chosen
none of which
are the cat's whiskers such as NEC based curve.
Art

"Ian White, G3SEK" 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?

There is a table of data calculated by VE7BQH for a large number of
different yagis, at:
http://www.ifwtech.co.uk/g3sek/diy-yagi/ve7bqh.htm
(These are not calculated by NEC, but by another very adequate program.)

You can draw your own curve from the data in the L(WL) and Gain columns.
Since all the data have been calculated by the same person, starting
from the antenna's mechanical dimensions, and using the same program,
this removes a lot of variables.

You will see a broad trend of increasing gain with boom length, but
there is still a lot of scatter due to variations between different
designs. Also bear in mind that gain isn't everything, and a long yagi
that has been maximized for gain may be a poor antenna in other ways,
such as sidelobe levels, ease of pointing, sensitivity to water on the
elements, ease of matching etc.

Drawing gain curves is a fun activity... but don't try to read too much
into them.


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

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