The antenna input of my radio is fed from a secondary coil of 4 windings; I know one or two windings is sometimes recommended, but I use it with a tube radio whos input impedance should be higher than that of a transistorized set. After all the radio was designed with a longwire in mind.

Experiment! Try a one or two turn secondary. Sometimes you have to throw the textbook and theory out the window. The original design for my 1 metre loop called for a single secondary winding, twisted about the fourth turn of a seven turn primary winding. I tried various coupling methods and eventually opted for a single turn spaced 2 cm below the fourth primary winding. Signal level became considerably reduced, but null/peak increased. My Icom R71A countered the reduced signal level. May, 1995 (Author of advice unknown)