The K9AY loop antenna can provide a cardioid (heart-shaped, single-null) pattern when one end of the antenna is connected to ground through a variable DC resistance. This occurs because of the interaction between electric and magnetic field pick-up patterns.

The antenna was first described by Gary Breed, K9AY, in QST magazine, September 1997, with an update in the QST of May 1998. Al Merriman, K4GLU, was the first to use this antenna for serious medium-wave DXing. A K9AY loop accompanied Al to Newfoundland on the very successful 1998 DXpedition. Andy Ikin of Wellbrook Communications in the UK has also done thorough tests on this antenna type. Read Al's discussion and the original QST articles for more information. The drawings I've provided are of a K9AY loop tested at sites in Billerica, MA and East Harwich, MA during 1999.

The BBL-1 Broadband Loop is a scaled-down version of this antenna. It is usually mounted on the roof of a car for seaside DXpeditions of brief duration. BBL-1 documentation is may be obtained in PDF format from links found on the WA1ION DX Lab home page (as listed below).