"Tom Donaly" wrote in message
m...
Yuri Blanarovich wrote:
Thus, the shield IS the antenna, and the loop is the means to couple the
energy out of the short dipole. Thus, it really isn't a magnetic antenna
at
all - it's a dipole!

Tom, W8JI has a better, more detailed explanation at his website (a great
resource) at http://www.w8ji.com/magnetic_receiving_loops.htm




Looks like another "debunked" fact by "Tom noname" W8JI. (Welcome back
Tom ?:-)

The shield IS an electrostatic SHIELD and wires inside are the ANTENNA.
If you want good efficient, electrostatically shielded small loop, take
copper
or aluminum tubing, bend it in a circle about 1m diameter (for around
160m
band). I made it of two pieces, joined at the bottom in metal electrical
box.
Top of the loop is open and insulated with plastic tubing. Then thread
wire
through the loop, three turns, bring the ends into the junction box and
connect
trimmer capacitor (about 1.5k ?) across the ends (not connected to
anything
else). Then thread another single turn loop through the tubing. In the
junction
box, connect one end to the coax shield and the second end to trimmer
capacitor
(about 500 pF ?) in series with the center conductor of the coax. Shield
and
mast holding it can be grounded at the installation place. I actually
used low
power transmiter and SWR bridge to tune the loop, now there are nice
antenna
analyuzers to do it. The three turns are resonated to operating frequency
with capacitor and that is
the ANTENNA. The single turn loop is the coupling and trimmer provides
match to
the coax feedline. The tubing is a SHIELD which helps with suppressing
the
noise and interference from nearby sources. I have also used this loop as
a coupling to Beverage antenna (positioned at the
end of Beverage), where it provided less noise than beverage alone.

Don't believe everything you read at W8JI web pages. I would like to see
a short "dipole" (NOT), really short piece of tubing, which
is attached to a mast and grounded to act as an antenna on low
frequencies.
Having small loop, insulated and properly fed or coupled to, is another
thing.
You can have single loop or turn antenna too, but above described antenna
is
"magnetic" or electrostatically shielded small loop antenna which
provides more
signal and better discrimination from nearby interference.

Yuri, K3BU.us

Don't believe everything you read here, either. For a good treatise on
how the shielded loop works, and what it's good for, read Glenn S. Smith's
(Georgia Institute of Technology) article "Shielded Loop
Antenna" in Richard C. Johnson's _Antenna Engineering Handbook_.
73,
Tom Donaly, KA6RUH

There is also a reasonably good discussion in the ARRL Antenna Book. The
section on direction finding antennas discusses the directivity of shielded
loops vs loop antennas.

Tam/WB2TT