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On Tue, 10 Nov 2020 at 12:07, Richard Hankins <g7rvi@...>
wrote:

On 09/11/2020 20:51, Dr. David Kirkby, Kirkby Microwave Ltd wrote:

2) You talk about efficiency of an antenna, but don't define it. Most
people don't have a clue what efficiency is. The generally accepted
definition amoung professionals comes from IEEE standard 145. Efficiency

is

the power radiated divided by the power absorbed by the antenna. Note the
word absorbed - it has nothing to do with the incident power. So if you
have a crap SWR, you transmit 100 W, 99 W gets reflected, and 0.95 W gets
radiated, then the antenna is 95% efficient, despite you would probably

not

consider it a very good antenna.

David,

surely the antenna in your example is fine - it radiates the power it
actually receives. What's crap is the matching ! Hardly the fault of
the antenna.....

Richard
G7RVI

Richar,
my point is, that on a document aimed at hams, on fundamentals, to use
efficiency, without defining it, is not a good idea. If this was an IEEE
Antennas and Propogation journal, it would be different.

As Jim Lux said, in response to my post

*"I agree - Efficiency is a tricky word when associated with antennas. I
try to stay away from it, ..."*

If the antenna impedance is 0.5 ohm, then it would have the 100:1 VSWR I
mention when measured in a 50 ohm system. That would be tricky to match to.
Efficient yes, but not easy to use.

I personally feel, that on something aimed at amateurs, to use the word
"efficiency" is not a great idea, unless one is going to describe in detail
about what efficiency is. It's one of those words, that 99% of hams will
not know the true meaning, but will all think they have a fairly good idea
of what it meant by an efficient antenna.

The original poster asked for feedback, so that is my thought on the
matter.

Dave