I have an AOR LA-350 active loop
(http://www.aoruk.com/direct/la350.htm) that outperforms every wire
antenna I construct outside, including the last one, which is over 100
feet in length using a matching transformer and coaxial feed.

Either this is one hell of an active loop or I really stink at
building antennas! I think I'm beginnning to see why some people
become loop fanatics.