Roy Lewallen wrote in
:

....
mode rejection. I'd be interested in hearing how Owen managed to get
good nulls from an unshielded loop.

Roy,

Perhaps some of this goes to the meaning of "good nulls".

I have just performed a simple test with the antenna described at
http://www.vk1od.net/SmallUntunedSquareLoop/index.htm .

I have inserted a step attenuator between the antenna and receiver, have
10m of coax draped over the ground, and measured the depth of null on a
nearby broadcast station on 1.2MHz. The depth of the nulls are between
30dB and 40dB, and the two nulls are within a couple of degrees of 180°
apart and of similar depth as you would expect from a loop with little
feed line contribution.

The nulls from this antenna are certainly very sharp for the purposes of
direction finding, they are orthogonal to the plane of the loop, and
symmetrical, the nulls or of similar depth. In my experience, the
smallest contribution of feedline pickup is shown as unequal nulls.

Owen