Someone recently mentioned the Wellbrook loop.

 

I borrowed a Wellbrook loop for antenna comparisons a while back. Weak signals on MF that i could copy with my 1/4 wave inv L on MF and also my 160m inv L also used to RX on MF. I could not even hear these weak signals on the Loop.

I could copy stronger signals on the Loop but these were 2 to 3 S units down on the above wire antennas.

A vertical loop is not ideal for all round listening except it is rotatable, but could be useful to null out noise at a noisy QTH

A resonated length of wire as long as possible would be a better choice for all round listening

de G3KEV