"K7ITM" wrote in message
oups.com...
Yuri,

It seems to me that when "W8JI" is associated with something, you
assume immediately that it is wrong.

That's what might seem to you, but I point out gross misinformation, when I
come across it. I express my opinion based on what I know or believe. I
could be wrong and I gladly get educated. Mostly, if I see, measure or touch
something, I believe it to be right. Mumbo-jumbo "scientwific explanation",
taking off on tangent to justify the fallacy don't cut it with me.

If you were to read Ronold W. P.
King's explanation about small loop antennas in "Transmission Lines,
Antennas and Waveguides", would you be any more apt to believe it? How
about Glenn S. Smith's discussion of them in Johnson and Jasik's
"Antenna Engineering Handbook" (second edition)? Each of those begins
with a reasonably detailed description of an "unshielded" loop and
moves on to a "shielded" loop.


I don't have the King's book, in Jasik's the treatment of small loops and
shielded loops is dealing with some "medieval" designs. The closest to my
version is his Fig. 5.23a showing balanced shielded loop. But then the
5-23bdoesn't make much sense to me, having small loop on the front of
reflector, when the small loop has the minimum of radiation along the axis
through the loop, and he places the reflector in the minimum - null
direction? The way they show the loops, half of loop solid wire, half coax
line, creates confusion what is antenna, what is shield, or perhaps combines
them. I have not used those designs.

In addition, can you expain to us how the current on the wires on the
inside of the shield is NOT balanced by an equal current in the
opposite direction on the inside surface of the shield? Please tell us
in detail just what currents are where on the shielded loop. If you
are going to try to tell us that some explanation is in error, please
provide us with enough detail that we can make up our own minds. So
far, all I've seen here is some vague reference to confusion about
shields.

The descriptions in each of the two references I gave above are far
more detailed than what you have posted here, either of your own or of
W8JI's, and I find them both enlightening--they are slightly different
from each other--but both detailed enough that you can make up your own
mind about what's really going on, and not have to read ranting
generalities or statements with nothing to back them up.

Cheers,
Tom


I will not get tangled into currents, phasors, but describe my design of
small shielded loop antenna that I used on 160m and this should perhaps shed
some light on the controversy.

I used 1/2" copper water tubing (non ferrous material passing the magnetic
field) for circular loop about 4 foot diameter. At the top the loop had gap,
at the bottom it was mounted in small metallic box. Loop, box and mast were
all DC connected and grounded. Mast was about 5 ft high, with Ham-m rotor at
the base to rotate the contraption. This formed Electrostatic shield for the
antenna.

From the connection box I threaded three turns of electrical house wire #12
and across the ends connected mica trimmer capacitor C1 (abt 1200 pF?) to
resonate the three wire loop antenna at 1.830 kHz). Not connected to
anything else, nor ground or loop.
Then I threaded one turn of the same #12 wire as a coupling turn. One end
was connected to the coax braid, the other end through another mica trimmer
capacitor C2 to the center conductor of the coax. Floating, not grounded or
connected to other loop or tubing.
I tuned the C1 to resonate the three turns at the desired frequency and C2
to provide 50 ohm match to coax. Circuit wise this mirrors the LC parallel
tuned circuit with link coupling and provide better signal than other
published designs.
I tried version of this without copper tubing shield and with. I had local
AC power line noise (within fractions of wavelength) and shielded loop
attenuated the local noise.
The way I see this works, the three turns were the antenna, it was tunable
across the band. The "link" coupling allowed to keep the symmetry of antenna
and provided some isolation for common mode currents between the antenna and
coupling (well known in LC tuned circuit with link coupling.). The copper
tubing was ELECTROSTATIC SHIELD which let's the EM waves pass through.
If the copper tubing IS the antenna, then how does it work? Short, grounded
in the center bent dipole? Then the radiation pattern should have maximum
perpendicular to the plane of the loop/dipole. But the antenna has NULLS in
that direction, corresponding to the properties of the 3 plus 1 wire loops.
You scientwists can play games with theories how it should behave, but the
reality again shows how it behaves. Anyone can build the antenna as I
described and VERIFY it. Wire loops without electrostatic shield tubing
still work the same way as with the shield. So which IS antenna?

Another description of the subject antenna is at
http://www.tpub.com/content/antennaa...-352-14_31.htm

73 Yuri Blanarovich, K3BU, VE3BMV