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I have been using spiral loops exclusively for reception of LW, MW, and SW many years.? I understand, despite their low radiation resistance, loops have become quite popular for transmission experimentation among hams in recent years.

The spiral geometry provides minimum distributed capacitance in a coil.? This leads to the possibility of a higher L/C ratio in a resonant circuit and greater sensitivity.? All my antennas are resonant primary circuits transformer coupled through a low-impedance coil and twisted pair to the receiver.? The secondary (coupling) loop must provide a good impedance match to the transmission line and have a suitable coefficient of coupling with the primary circuit.

My current articles in the files section are as follows:

PRTC Loop Antenna - 2022_02_14.pdf is a 3' diagonal spiral covering 2.6 to 12.1 MHz.

Electrically Small Resonant Loop for Shortwave (Oct '14).pdf is a 2' diagonal version covering approximately the same band of frequencies.

Electrically Small Resonant Loop Antenna for Mediumwave Reception.pdf is the current draft of my MW article, which identifies a lot of my engineering sources, theory, and construction details.

Hope some of this is helpful.

Bob C.