"Richard Clark" wrote in message
...
On Sat, 10 Apr 2004 08:37:09 -0700, Bill Turner
wrote:
Bill

How does a person measure the gain of an antenna?

Jerry

Carefully, I would hope.

Hi Bill,

Your response hardly carries the water for an argument supporting gain
being commonly distinct from directivity.

To answer Jerry's question (he probably already knows how) requires
the total integration of all power emitted by the radiator - not an
easy task (as would confirm Bill's sparse reply) and then measuring
power emitted within small volumes (solid angles of sub-radian
dimension) to compare against the whole.

The most distinctive point to observe about this "gain" is that almost
all the power radiated is lost - "almost" being a patronizing term. A
simple thought problem will reveal this sad fate.

Let us presume you are transmitting 100W with 100% efficiency. Now,
lets further presume that the entire population of the planet is
monitoring you with S-9 readability. That is (let's be generous), 10
Billion receivers. What is the net result of this massive
communication in system efficiency?
0.5%

The antenna in the most perfect of circumstances exhibits an absolute
loss of 99.5W and I could easily bet no one here even pretends to
approach 0.000001% of this.

Now, tell me about GAIN. :-)

73's
Richard Clark, KB7QHC

Wow Richard, measuring antenna gain sounds complicated. I never was good
at calculus.

Jerry

On Sat, 10 Apr 2004 20:12:08 GMT, "Jerry Martes"
wrote:
Wow Richard, measuring antenna gain sounds complicated. I never was good
at calculus.

Hi Jerry,

That's for software to do.

73's
Richard Clark, KB7QHC

On Sun, 11 Apr 2004 08:36:19 -0700, Bill Turner
wrote:
For ham radio purposes, antenna gain and
directivity are essentially interchangeable.

Close enough for Government work.

On the other hand, if you try that on your dissertation for your PhD in
physics, you may end up working at McDonalds.

Hi Bill,

My first assignment out of Metrology school was in Charleston S. C.
loaned to the SeaBees (because my ship was still in Rota Spain). They
took full stock of my million dollar training and found I was
qualified to dig ditches in the clay banks along the Charles river.
They were impressed I knew which end of the shovel went into the
ground and we became fast friends (made me an honorary SeaBee).

Navy motto, "those that work hard together, play hard together" (I
had already learned that from my Pig-boat buddies.)

73's
Richard Clark, KB7QHC

On Sat, 10 Apr 2004 17:29:56 GMT, Dave Shrader
wrote:

Knowing the angles the 'Gain' is calculated by dividing 41259 by the
product of the horizontal and vertical angles corresponding to the 1/2
power point. [Note: 41259 is the surface of the sphere measured in
square steradians.]

I'm sure that most are aware that a sphere has 4 Pi steradians, but
you've lost me with your number 41259, and what is a "square"
steradian? I've never heard of such a thing.
Bob, W9DMK, Dahlgren, VA
http://www.qsl.net/w9dmk

Bill

First - I want to be clear that I have absolutely no problem with using
the term GAIN for describing antenna performance.
I did think had not been established, in this thread, that an antena's
gain has to be referanced to some standard antenna, like a dipole or
theoretical radiator like 'isotropic'. I'd submit that, what we refer to as
antenna gain could be more accurately be called 'specific gain'. I also
tink that the term Directivity clears up any misunderstanding about what can
be done to improve an antenna's performance. And, I realize that my
thinking about Gain and about Directivity dont imply that anyone needs to
exclude either from their vocabulary

I suspect my caution about antenna gain stems from reading specs that
display extremely high "gain" numbers while the antennas are actually quite
ordinary.

Jerry


"Bill Turner" wrote in message
...
On Sat, 10 Apr 2004 15:59:56 GMT, "Jerry Martes"
wrote:

I'll be carefull if you'll tell me how to do it.

Jerry

__________________________________________________ _______

Only one "l" in careful Jerry, not a good start. :-)


1. Decide on your reference, most likely a dipole.

2. Measure the field strength of the dipole in its most favored
direction.

3. Measure the field strength of the antenna under test in its most
favored direction.

4. Calculate the gain or loss of the antenna under test.

5. Post the results here and be prepared for an onslaught of criticism.

--
Bill, W6WRT
QSLs via LoTW

I suspect my caution about antenna gain stems from reading specs that
display extremely high "gain" numbers while the antennas are actually
quite
ordinary.

Absolutely. Whenever I see a gain number that dosen't reference something,
I assume they mean dBi, rather than dBd.

Dave VanHorn wrote:
Absolutely. Whenever I see a gain number that dosen't reference something,
I assume they mean dBi, rather than dBd.

Looks like some antenna retailers reference dBdl. :-)
(dl stands for dummy load)
--
73, Cecil, W5DXP



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"Cecil Moore" wrote in message
...
Dave VanHorn wrote:
Absolutely. Whenever I see a gain number that dosen't reference
something,
I assume they mean dBi, rather than dBd.

Looks like some antenna retailers reference dBdl. :-)
(dl stands for dummy load)

I've seen a few antennas that should be spec'd as negative dBdl.

On Sun, 11 Apr 2004 13:31:22 -0500, Cecil Moore
wrote:

Dave VanHorn wrote:
Absolutely. Whenever I see a gain number that dosen't reference something,
I assume they mean dBi, rather than dBd.

Looks like some antenna retailers reference dBdl. :-)
(dl stands for dummy load)

Actually it appears as if some manufacturers only measure the
directivity and express it in dB :-), completely ignoring the
efficiency, which is often quite low in "exotic" antenna designs.

An exotic antenna design with directivity 10 (10 dB) and 10 %
efficiency will have a 0 dB gain and will produce the same effective
radiation power (ERP) as an omnidirectional (directivity 1 or 0 dB)
antenna with 100 % efficiency when using the same transmitter power.

Paul OH3LWR