Roy Lewallen wrote in message ...
I hope you'll pardon me for amplifying this a little.

If you put X watts into the primary of a transformer and extract Y watts
from the secondary, the efficiency is Y/X by definition.

Yes Roy. The specifics of what is being discussed is all important
when looking at answers as well as what terms are being used to
measure 'efficiency' and to what ends.
As you are surely awawe I too look at antennas as transformers or
coupled circuits and thus the primary contributes very much in its own
way as far as radiation as does the secondary. Thus 'efficiency' as a
criteria of 'value'
is all important when using it as a term since as you point out it is
a ratio of two terms both of which have to be made very clear for the
term efficiency to be made clear
Thus in stagger tuning it is important to define your requirements in
terms of bandwidth (dual frequency radiation) or max gain ( dual
radiators on the same frequency),the above bearing little difference
to old time receiver designwith multiple I.F. cans. It is in this
areana that I view stagger tuning or coupling
as being efficient in charactor. If I am incorrect in the above
assumptions I would welcome any correction from those well versed
inthe field.
Best regards
Art


If you put X watts into one antenna and extract Y watts from an antenna
coupled to it, and measure the efficiency of the "transformer" the same
way as you did the conventional transformer, you'll find it has lousy
efficiency. Why? Because a goodly fraction of the power you applied to
the "primary" antenna never gets to the "secondary" antenna because it's
radiated instead. As far as the "secondary" is concerned, it might as
well have been converted to heat.

If you look at the impedance of the "primary" antenna, you'll find an
excess of resistance -- just enough, in fact, to account for the "lost"
(radiated) power.

This isn't a statement about how well coupled antennas function as
antennas, whose purpose is to radiate after all. It's a statement about
how well they function as a transformer. Poorly.

Roy Lewallen, W7EL

Dr. Slick wrote:
(Art Unwin KB9MZ) wrote in message m...

1. Two antennas (also called transducers) placed close together
actually can be considered a transformer, albeit a very inefficient
one.

Humm...By antenna I assume it also means a radiator. This would
suggest
that a stagger tuned radiators would fall into the catagory discussed
above.
Now I have a problem with that statement, because I very much see it
as a transformer which is VERY efficient and not as you stated "albiet
a very inefficient one".
Can you explain to me how a stagger tuned antenna migrate into
inefficient radiators?
Seems to me that Thevenin's theorem would show this as being
incorrect !




Well, two identical antennas spaced a few wavelengths apart can
be considered a transformer, but very inefficient compared to a "real"
transformer with identical primary and secondary turns, with an
appropriate toroid core. This would be because the core material will
increase the magnetic flux density, and will increase the coupling
between the two windings/transducers.

Point is, the farther apart the antennas are, the less efficient
of a "transformer" they will be.

I'm not familiar with stagger tuned antennas, although the name
would suggest that it is tuned for multiple resonances, so that the
antenna will be broadband.



Slick