On Wed, 13 Jun 2012 15:11:06 -0700, "garyr" wrote:

This site http://www.frontiernet.net/~jadale/Loop.htm states that: "A
properly designed Loop primarily responds to the magnetic component of the
radio wave. Note that noise resides primarily in the electrical
component..."

Whereas this site shows that that is not the case:
http://vk1od.net/antenna/shieldedloop.

So what is the advantage, if any, of a shielded loop antanna?

Consider three receivers:

1) Shielded loop antenna, receiver with differential input (center-tapped
transformer or instrumentation amp). The two ends of the inner conductor
of the antenna connected to the differential inputs and the shield
connected to ground.

2) Same as above but without the shield.

3) Unshielded loop antenna, receiver with single-ended input.
One end of the loop connected to the receiver input and the other to
ground.

Assuming equal gains and bandwidths, would there be any
difference in the sensitivity or noise level at the output of the three
receivers?

A loop is a loop is a loop, meaning that one side conductor goes
upwards while the other side goes downwards in contrast to a
linear wire antenna or a dipole which is extending in one direction
only. The up-and down (left and right) parts of the wire cancel out
each other at least partially when collecting energy from an electric
field, while the energy uptake from a magnetic field is proportional
to the loop area.
This electric noise cancellation is not perfect, due to unsymmetries
in the field, therefore it pays to shield the loop wires and decrease
the electric influences further.

I hope my explanation is simple enough.

w.