On Mar 31, 8:04 pm, Jim Lux wrote:
Mike Kaliski wrote:
Hi Richard,

I have a pair of computer speakers sitting on my desk that completely
out perform the so called ultimate hi-fi floor mounted tower system
speakers I bought 35 years ago for the equivalent of several thousand
dollars in today's money. The old speakers still work just fine but the
audio experts have learned how to squeeze that performance out of a
speaker that old audio theory predicted couldn't possibly work. Just how
does a 3 inch speaker in a cabinet the size of a couple of books manage
to produce notes from 20 Hz - 20 kHz? To be fair, the small speakers
can't fill a room with sound in the same smooth way that a larger
speaker cabinet can, but for everyday use in a small modern house or
apartment they are more than adequate for the majority of people.

It seems to me that Art and others are pursuing a similar path at RF.
The aim being to produce an antenna that punches out a signal from a
physically small area. It may not perform quite as well as a full size
half or full wavelength antenna, but it will work well enough for most
people with small gardens or limited real estate for an antenna farm.

Nope.. there's a significant difference between the speakers and the
antenna, and that's the fact that the amateur user of the antenna is
power limited (by regulation). In the speaker case, they trade off
efficiency (acoustic watts out for electrical watts out) because
electrical watts are cheap these days (not so back in McIntosh tube amp
days...) You can tolerate a 1% efficient design that puts out 100mW of
acoustic power with 10W electrical power in. (note that 120dB SPL = 1
Watt.. a symphony orchestra, at full tilt, is about a watt of acoustic
power, and I daresay you couldn't tolerate a whole orchestra in your office)

OTOH, a 1% efficient antenna design is pretty crummy. A dipole is
probably on the order of 70% efficient (RF power radiated into the far
field vs RF power at the feedline). A mobile antenna (which everyone
will agree is not particularly efficient, even if you argue about the
actual magnitude) might be 5-10% efficient (10dB down).

As a practical matter, you can get away with a 1% efficient antenna,
particularly if you're not looking for "link reliability"... The
propagation loss between you and some arbitrary point could easily vary
by 100 dB, so you just wait until propagation is "good enough" to work
the guy with the 0.1W you radiate. Of such are "worked 300 countries on
two bedsprings" sorts of stories made. Folks work around the world on
less than a watt radiated, just not "on demand".. they keep trying until
conditions are just right and they "get lucky".

So, on that basis, you could probably fire up your 1500W amplifier into
a compact loop antenna that's a meter in diameter, and work the world,
eventually.



Clearly there are considerable differences in dealing with sound waves
and RF but I believe that a principle has been established that it is
possible to 'simulate' the performance of a larger system using
physically small components. Art may not be the first to get there, but
he seems to be having a damn good try and someone, somewhere will
eventually succeed.

Mike G0ULI

Believe it or not Jim but I presently have a 160 meter antenna (full
wave)
wound on a metre loop that is resonant and can be used to work the
world.
It is hanging in the yard right now and obviously is very efficient at
what it does.
Covers the whole band to. Paid a dollar at the dollar store for the
hoola hoop!
Don't need to add capacitors and inductances evry few KHZ !
Art