On Wed, 27 Apr 2005 09:26:48 -0400, "J. Mc Laughlin"
wrote:

Well reasoned.

Think of a three-dimensional curve of cost, uncertainty, and frequency to
measure gain on a range. Think of a second 3D curve involving modeling. My
guess is that below something like 20 MHz (use your own number) modeling is
to be preferred.


On a related topic: I saw with my own eyes NBS in Boulder (c. 1978)
using a different technique to measure gain. It was a near field scheme
where a probe was moved in front of the antenna while its vector voltage and
position was measured. (As I recall, a pair of lasers was used in the
measurement of the probe's x and y position.) The (vast number of)
measurements were then imported into a computer that computed the gain. As
we say: "you could do that!" I never thought to ask what the expected
uncertainties were expected to be.


http://www.nearfield.com/

Richard Clark wrote:
"Capture area of antennas, 899, 927 of Yerman`s "Electronic and Radio
Engineering"."

"Capture Area" seems useful to show that the maximum energy you can
intercept in a wave is proportional to the product of directive gain and
wavelength squared.

Terman`s examples show that the microwave antenna`s high gain is offset
by the extremely short wavelength.

There is only so much energy in a square meter of passing wave. Large
antennas access more of it than small ones. I don`t often need to make
these calculations.

Richard Clark also says Bailey is "naively assuming a 3 dB gain with
each doubling of elements."

It seems to me that the 2nd, 4th, and 8th element may have the same
flaws as the first. No matter how good or bad they are, if they are all
similar, wouldn`t (n) elements abstract nX the energy in one element?

One of my favorite gems in the newest Kraus "Antennas" is the solved
problem on page 705.
Solution:
(A) The gain of a simple 1/2-wave dipole is 2.15 dBi and of 2 collinear
in-phase dipoles is 3.81 dNi. The array of 8 such collinear dipoles adds
3 +3 = 9 dB. The reflector screen adds 3 dB more and the ground bounce
another 6 dB for a total gain of 3.8 + 9 +3 +6 = 21.8 dBi."

This is the gain of the Deutche Welle antenna which appears on the rear
cover of my copy.

Best regards, Richard Harrison, KB5WZI

Richard Clark wrote:
On Wed, 27 Apr 2005 03:11:34 GMT, "
wrote:


a basis for rejecting.
new knoweledge supplied by computor programs


Hi Art,

More baloney cut thick. You have NOWHERE offered any discussion of
ANY new knoweledge (sic); but you hug such manufactured sentiments
like an emotional life preserver.

You rctleeny challngeed Roy for his athortuy. You wloud do well to
leran spllenig bfoere ripeteang that aigan.

What I want to know is how we are going to alter reality when the
computer program shows it is wrong!




- Mike KB3EIA -

Richard Harrison wrote:
. . .
Richard Clark also says Bailey is "naively assuming a 3 dB gain with
each doubling of elements."

It seems to me that the 2nd, 4th, and 8th element may have the same
flaws as the first. No matter how good or bad they are, if they are all
similar, wouldn`t (n) elements abstract nX the energy in one element?
. . .

Yes, but the amount extracted by one element is affected by the presence
of the others. So adding or removing an element changes the amount
extracted by all the other elements. The effect is known as "mutual
coupling", and it explains why, for example, a 2 element Yagi or other
two element array can have gain greater than (or less than) 3 dB
relative to a single element.

Roy Lewallen, W7EL

Roy Lewallen, W7EL wrote:
"Yes, but the amount extracted by one element is affected by the
presence of the others. So adding or moving an element changes the
amount extracted by all the other elements."

Thank you. Mutual impedance can add or subtract from a total. I assumed
the designer would be deliberately combining elements in such a way as
to maximize total gain. Plans don`t always work the way we hope.

Best regards, Richard Harrison, KB5WZI

Richard Fry posted a beautiful picture of a Harris / Gates test facility
in which an antenna tower is rotated and tilted up to 90-degrees, I
suppose. Nice way to get the antenna pattern. Hope Harris had a
government contract number to charge that job to.

Best regards, Richard Harrison, KB5WZI

From: "Richard Harrison"
Richard Fry posted a beautiful picture of a Harris / Gates test facility
in which an antenna tower is rotated and tilted up to 90-degrees, I
suppose. Nice way to get the antenna pattern. Hope Harris had a
government contract number to charge that job to.
________________

Azimuth patterns were taken by spinning the antenna+tower around a
horizontal axis centered above the two trestle supports you see in the
scanned photo. The AUT is positioned broadside to the source antenna.

Elevation patterns were taken by spinning the whole assembly in the
horizontal plane, on the horizontal centerline of the antenna+tower
assembly. The trestles sit on a huge wooden beam which itself is supported
by, and centered on a motor-driven turntable -- making that possible.

So both sets of patterns can be taken without needing to put the
antenna+tower in the vertical plane (no tilting to 90 degrees is necessary).

However we had several other positioners for vertical antennas to use when
the measurement of elevation patterns was not required.

Yes, this customer had deep pockets, but was not a government agency. Just
a major broadcast group.

RF

Correction. Even identical array elements *don't* necessarily extract
the same amount of energy. The reason again is mutual coupling. In a
four-square receiving array with very low ground loss, one of the
elements will actually radiate power. This power comes from power
extracted from the wave by the other three. In a Yagi array, the
parasitic elements extract no power at all from an impinging wave; only
the driven element does.

Roy Lewallen, W7EL

Roy Lewallen wrote:
Richard Harrison wrote:

. . .
Richard Clark also says Bailey is "naively assuming a 3 dB gain with
each doubling of elements."

It seems to me that the 2nd, 4th, and 8th element may have the same
flaws as the first. No matter how good or bad they are, if they are all
similar, wouldn`t (n) elements abstract nX the energy in one element?

. . .

Yes, but the amount extracted by one element is affected by the presence
of the others. So adding or removing an element changes the amount
extracted by all the other elements. The effect is known as "mutual
coupling", and it explains why, for example, a 2 element Yagi or other
two element array can have gain greater than (or less than) 3 dB
relative to a single element.

Roy Lewallen, W7EL

Roy Lewallen, W7EL wrote:
"Even identical array elements "don`t" necessarily extract the same
amount of energy. The reason is again mutual coupling."

Yes, and driven elements have a load. Parasitics do not.

In a parasitic array, the field strength at a distant point is a
function of the currents in both elements when it consists of two
dipoles.

It is true "the parasitic element extracts no power from an impinging
wave". It has no load to accept the power. It is a short-corcuit rod or
wire. It has current induced from a passing wave of acceptable direction
and frequency whether its source is from a driven element or from a far
away transmitter.

The excitation of a parasitic element, if no heat is produced in the
slemsnt. is 100% re-radiated. The element has a resistance which
consists of its self resistance and its mutual resistances. The total
composes the radiation resistance of the element which is the source
resistance for the radiation from the element.

My original comment was in support of Arnold B. Bailey who said
something about increasing antenna gain by 3 dB every time you double
its size. Precisely, that`s not true, but I gave an example from Kraus
where he did much the same thing.

Best regards, Richard Harrison, KB5WZI

Richard Clark wrote:

On Tue, 26 Apr 2005 20:28:01 -0500, Tom Ring
wrote:

Any references on microphone calibration? Maybe a short tutorial? That
is something I have a need to do.


Hi Tom,

Standard microphones (I am being quite specific in terminology here)?

I googled with the terms
B&K microphone reciprocity
snip
73's
Richard Clark, KB7QHC

Thanks.

tom
K0TAR