mario wrote:
On Sat, 24 Nov 2007 23:41:19 -0800, Roy Lewallen wrote:
In my limited experience, it's extremely difficult or impossible to do a
good job of isolating the feedline from a small loop. The common mode
impedance is just too high.

Roy Lewallen, W7EL

Hello

How much (estimated) would this common mode impedance be for a 3 foot
diameter loop for instance 80 meter band?

It depends on height above ground, but according to EZNEC it's on the
order of 1000 ohms when 6 feet above ground. You'd probably need a
receiver or circuit with differential input and very good common mode
rejection ratio, and perhaps also an exceptionally good balun, to
prevent the feedline response from reducing the null depth unless using
a "shielded" loop which by its construction provides good common mode
rejection. I'd be interested in hearing how Owen managed to get good
nulls from an unshielded loop.

Roy Lewallen, W7EL