On Sun, 24 Apr 2005 19:38:10 GMT, "
wrote:

|
|"Richard Harrison" wrote in message
...
| Reg, G4FGQ wrote:
| "Naturally, laboratories can differ one from another."
|
| A lab may put its stamp of approval on your instrument, but your best
| assurance may be measurement of known values. The temperature of
| ice-water or the voltage of new dry cells, for example You usually can
| try several dry cells for confirmation or averaging.
|
| In antennas, one strategy for successful gain determination is
| comparison with an antenna of known gain.
|
|Whow, thats a good idea, write it up for QST. They are looking for pearls of
|wisdom
|that can be useful for ham radio operators so that we may maintain our
|perceived
|leadership of the art of antennas......'Compare with a antenna of known
|gain'...... Revolutionary!
|Now why hasn't any Guru on this group thought of this before today?

Perhaps because it's so commonplace that it doesn't bear mentioning.

|Now we have to decide what we use to measure the gain and more important
|not to compare or to compare at a single recieving point especially if the
|receiving depends
| on skip or propagation. Is it possible that Guru's are unaware that
|elevation angles
|can be different when comparing antennas? Another gem for the ARRL and
|provided
|solely by the leading gurus of AMATEUR radio operators no less. Ofcourse we
|need
|a telephone link with the country that we wish to hear the transmission,
|some thing on the simple lines of
|...."can you hear me now"
| question as we switch antennas
|between a dipole and a drape / curtain array every 5 minutes

If you believe that precision antenna gain measurements are made under
ionospheric propagation conditions, you are clearly delusional. But I
repeat myself.

"Wes Stewart" *n7ws*@ yahoo.com wrote in message
...
On Sun, 24 Apr 2005 19:38:10 GMT, "
wrote:

|
|"Richard Harrison" wrote in message
...
| Reg, G4FGQ wrote:
| "Naturally, laboratories can differ one from another."
|
| A lab may put its stamp of approval on your instrument, but your best
| assurance may be measurement of known values. The temperature of
| ice-water or the voltage of new dry cells, for example You usually can
| try several dry cells for confirmation or averaging.
|
| In antennas, one strategy for successful gain determination is
| comparison with an antenna of known gain.
|
|Whow, thats a good idea, write it up for QST. They are looking for pearls
of
|wisdom
|that can be useful for ham radio operators so that we may maintain our
|perceived
|leadership of the art of antennas......'Compare with a antenna of known
|gain'...... Revolutionary!
|Now why hasn't any Guru on this group thought of this before today?

Perhaps because it's so commonplace that it doesn't bear mentioning.



That's what I thought. So why did Richard say it unless he felt that Reg's
education in antennas was a bit lacking. Reg's question was specific and of
high caliber
Richard's answer tried to bring it down to a level for dummies which did
not begin
to reflect on the question posed



|Now we have to decide what we use to measure the gain and more important
|not to compare or to compare at a single recieving point especially if
the
|receiving depends
| on skip or propagation. Is it possible that Guru's are unaware that
|elevation angles
|can be different when comparing antennas? Another gem for the ARRL and
|provided
|solely by the leading gurus of AMATEUR radio operators no less. Ofcourse
we
|need
|a telephone link with the country that we wish to hear the transmission,
|some thing on the simple lines of
|...."can you hear me now"
| question as we switch antennas
|between a dipole and a drape / curtain array every 5 minutes

If

Yes ,,,a big "IF" isn't it?
But you could supply the info Reg was looking for since you
perceive yourself as a GURU .
It would be much more rewarding to the group as a whole than
picking out somebody to demean.My point is that a gain figure alone
is meaningless unless the elevation angle differences or perhaps a
3 dB window comparison are also supplied.
If you think otherwise I would welcome a technical response
rather than something lead by emotion

Art



you believe that precision antenna gain measurements are made under
ionospheric propagation conditions, you are clearly delusional. But I
repeat myself.

Art Unwin wrote:
"My point is that again figure alone is meaningless unless the elevation
angle differences or perhaps a 3 dB window comparison are also
supplied."

Reg knows very well that a quantity is determined by comparing it with a
known standard.

The power gain of a resonant dipole in free-space is given by Terman on
page 871 of his 1955 edition as 1.64.

Kraus agrees on page 54 of his 1950 edition and converts Terman`s power
gain of 1.64 to 2.14 dB (referenced to an isotropic).

The values given by Terman and Kraus are accepted.

Horizontal antennas at the same heights tend to have similar elevation
angles, but even if they didn`t, comparison of the signals our two
antennas laid on the target represented our interest in the matter.

What we confirmed was that the new curtain antenna had a gain comparable
with our rhombics but over a wider beamwidth which meant listeners on
the edges of our coverage got a better signal with the new curtain
antenna.

The bandwidth was less than a phombic so the curtain meant more work for
the operators, but the broadcasts were for the listeners` benefit.

Signal strengths were measured at many locations around the target area
to define the coverage of the antenna pattern.

Best regards, Richard Harrison, KB5WZI

Richard, why don't you just say that the angle of elevation of the
radio path has nothing whatsoever to do with the type of transmitting
and receiving antennas, or the directions in which they may be
pointing or elevated, or even the operating frequency.

When communication has been established between A and B, the angle of
elevation depends only on the locations of A and B on the Earth's
surface, on the number of hops, on the height of the ionospheric
layers, and on the slope of the layers.

The elevation angle is determined purely by trigonometry.

It tends to be the same at both A and B. There may be simultaneously
more than one path and therefore more than one angle. In which case
multi-path distortion and fading occurs.

Received signal strength depends on the two antenna gains in the
direction of the path. The take-off angle predicted by Eznec-type
programs is an altogether different thing. It depends on reflections
from the ground in the vicinity of the two antennas. It does however
have an effect on received signal strength but is of use only when the
locations of A and B and all other geographic and ionospheric
variables are known. They seldom are! As are ground conditions.
----
Reg, G4FGQ.

Reg, G4FGQ wrote:
"Richard, why don`t you just say that the angle of elevation of the
radio path has nothing whatsoever to do with the type of transmitting
and receiving antennas or the directions in which they may be pointing
or elevated, or even the operating frequency."

Confuse the readers?

Geometry and trigonometry are involved. What`s more, the signal may take
more than one path between only two points, or multiple hops, or
multiple azimuths. This causes fading and distortion.

Transmitted energy in directions other than to a receiver is wasted.
That`s one of several reasons to use antenna directivity in azimuth and
elevation.

Maybe Cecil`s IEEE Dictionary defines TOA. The references I`ve found are
to "elevation angle" above the horizon.

In general, an antenna`s angle of maximum response is lowered by raising
the antenna height. If you have stacked horizontal elements you can
adjust their phasing to skew the elevation angle up or down some.

An ideal HF antenna may be a giant array of dishes that might be aimed
for one-hop, if possible, in a multiple diversity system.

Something almost as good is a triple diversity system which uses
rhombics. 3 receiving rhombics are plavced with about 10-wavelengths of
lateral spacing at the lowest frequency received. Multicouplers on each
rhombic feed various receivers , often at various frequencies. Diversity
combiners select the best received signal of three carrying the same
program. The results are spectacular. We used such TDR systems for
broadcast program relay. Often the quality was as if the program arrived
by cable.

Best regards, Richard Harrison, KB5WZI

Richard Harrison wrote:
Maybe Cecil`s IEEE Dictionary defines TOA. The references I`ve found are
to "elevation angle" above the horizon.

Nope, none of my references mentions TOA.
--
73, Cecil http://www.qsl.net/w5dxp


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I believe "takeoff angle" is in the same category as "capture area" and
"S-unit" -- terms which nobody except amateurs seem to need.

Roy Lewallen, W7EL

Cecil Moore wrote:
Richard Harrison wrote:

Maybe Cecil`s IEEE Dictionary defines TOA. The references I`ve found are
to "elevation angle" above the horizon.


Nope, none of my references mentions TOA.
--
73, Cecil http://www.qsl.net/w5dxp

Reg Edwards wrote:
Richard, why don't you just say that the angle of elevation of the
radio path has nothing whatsoever to do with the type of transmitting
and receiving antennas, or the directions in which they may be
pointing or elevated, or even the operating frequency.

Or even the existence of the human race and their radio transmitters.
The propagation paths are still there, and even if we had never invented
radio they would still exist.

Antenna engineering is all about making the best use of the propagation
paths that Nature provides[*].

That basic fact should be "bleedin' obvious".

[*] The HAARP project does aim to change the ionosphere itself - but the
colossal size and power of HAARP only goes to show that "the rest of us"
can NOT do that. We cannot change propagation; we can only use it.

When communication has been established between A and B, the angle of
elevation depends only on the locations of A and B on the Earth's
surface, on the number of hops, on the height of the ionospheric
layers, and on the slope of the layers.

The elevation angle is determined purely by trigonometry.

A handy phrase that hasn't been mentioned yet is "ray tracing". That is
what we're doing, same as in optics.


Received signal strength depends on the two antenna gains in the
direction of the path. The take-off angle predicted by Eznec-type
programs is an altogether different thing.

Hmm... at the risk of proliferating TLAs, how about making a fresh start
and calling that the antenna's BVA - Best Vertical Angle?

BVA belongs to the antenna, and TOA belongs to the propagation path.

It doesn't get around the fact that the antenna radiates something at
*all* vertical angles, but it's better than the present situation of
(mis)using TOA for two different things.


--
73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek

I too am reluctant to enter this as much resembles a freshman poli-sci
student debating a third year law student.

However .... please see indented comments below

--
J. Mc Laughlin; Michigan U.S.A.
Home:

"Reg Edwards" wrote in message
...
Richard, why don't you just say that the angle of elevation of the
radio path has nothing whatsoever to do with the type of transmitting
and receiving antennas, or the directions in which they may be
pointing or elevated, or even the operating frequency.

When communication has been established between A and B, the angle of
elevation depends only on the locations of A and B on the Earth's
surface, on the number of hops, on the height of the ionospheric
layers, and on the slope of the layers.

OK as far as the statement goes.


The elevation angle is determined purely by trigonometry.

Geometry might have been a better term, but the idea is right.


It tends to be the same at both A and B. There may be simultaneously
more than one path and therefore more than one angle. In which case
multi-path distortion and fading occurs.

Here I must inject my experience. As part of a topic sentence, "tends to be
the same" is OK. However, it is common on real HF paths of over 4 or 5 Mm
for the elevation angle at which the strongest signal arrives to be
significantly different at the two ends of the path. It is easy on longer
paths for the major mode at one end to be using a high virtual-height F2
mode and for the other end to be using a low virtual-height E mode.

Allow me to put to rest the notion that optimum elevation angles are
necessarily the same at both ends of a longer (multiple hop) HF path! [Reg
did not say that optimum elevation angle are necessarily the same.]

As other have said, but not all have heard, the idea is to maximize gain
(at both ends of a path) at the elevation angle being used. Even in the
20s, antenna systems were in regular use that attempted to do just this.


Received signal strength depends on the two antenna gains in the
direction of the path.

Agreed. Such an azimuth is not always along a great-circle.

The take-off angle predicted by Eznec-type
programs is an altogether different thing. It depends on reflections
from the ground in the vicinity of the two antennas. It does however
have an effect on received signal strength but is of use only when the
locations of A and B and all other geographic and ionospheric
variables are known. They seldom are! As are ground conditions.

What does exist is a stochastic model of the ionosphere that allows one to
make useful estimates of what is going to happen along a path. As has been
said many times here, all estimates and measurements comprise at least two
numbers: the best estimate and an estimate of the estimate's uncertainty.
Even if it were possible to do so, one would not use an antenna that had all
of its gain at the predicted optimum elevation angle. One would try to
design an antenna (money enters here) that has most of its gain in the
expected band of elevation angles expected to be best for a path.

----
Reg, G4FGQ.



73 Mac N8TT

J. Mc Laughlin wrote:
I too am reluctant to enter this as much resembles a freshman poli-sci
student debating a third year law student.

However .... please see indented comments below

. . .

Here I must inject my experience. As part of a topic sentence, "tends to be
the same" is OK. However, it is common on real HF paths of over 4 or 5 Mm
for the elevation angle at which the strongest signal arrives to be
significantly different at the two ends of the path. It is easy on longer
paths for the major mode at one end to be using a high virtual-height F2
mode and for the other end to be using a low virtual-height E mode.

Allow me to put to rest the notion that optimum elevation angles are
necessarily the same at both ends of a longer (multiple hop) HF path! [Reg
did not say that optimum elevation angle are necessarily the same.]

. . .

I'm glad you did get yourself to contribute to the discussion. I'm by no
means an expert when it comes to propagation (and quite apparently
several other participants aren't either), and I've fallen victim to
using oversimplified models where their use isn't appropriate. The
little reading I've done on the topic shows there are some really
interesting phenomena involved which don't at all fit with the notion of
simple reflection or refraction from a layer at a single height. Thanks
for reminding us about one of the more important ways in which the
simplified models are misleading.

As other have said, but not all have heard, the idea is to maximize gain
(at both ends of a path) at the elevation angle being used. Even in the
20s, antenna systems were in regular use that attempted to do just this.

. . .

Even if it were possible to do so, one would not use an antenna that had all
of its gain at the predicted optimum elevation angle. One would try to
design an antenna (money enters here) that has most of its gain in the
expected band of elevation angles expected to be best for a path.


Agreed.

Roy Lewallen, W7EL