RadioBanter - View Single Post - 50 Ohms "Real Resistive" impedance a Misnomer?

July 20th 03, 08:10 PM

(Art Unwin KB9MZ) wrote in message om...

Slick

Dr Slick,
Way back in this thread you alluded to antennas as being
transformers. The more I think about that statement the more I see
it as being fact. Anything that involved coupling which all
antennas do can be drawn as a transformer !
Since the thread migrated all over the place did you feel that
the group agreed with that position?
Regards
Art

Some have emailed me personally, and we have pretty much agreed on
these two points(even Roy agreed with these, if you read his posts
here):

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

So an antenna can be considered 1/2 of a full transformer, so i wasn't
that far off from a semantics point of view.

2. An antennas input impedance will depend on the impedance or
permeability of the medium it is radiating into. In other words, an
antennas free space input inpedance will be different from the input
impedance of the same antenna immersed in water.

This is of course with a completely water-proofed antenna.

I went on to point out that a toroid transformer of a specific
turns ratio, wire gauge, and core geometry, will definitely depend on
the permeability (impedance) of the core material for it's
characteristics.

Alas, i'm just a lowly practical engineer and not a PhD in EM
wave-propogation (obviously no one else here is either). But if a
transformer depends on 2 transducers' abilities to turn V and I into E
and H (and vice versa), and that this depends on the impedance of the
medium between them....then to me, an antenna is in some way
"matching" to the impedance of free space, 377 Ohms, even if the
energy has been converted to a different form.

Slick