English: A large indoor loop antenna for broadcast receivers, from a 1926 advertisement in a radio magazone. Dimensions: 8 in x 7 in x 30 in. high. It consists of many turns of fine wire on a mahogony frame, with a second loop inside the first. The second loop could be used to apply feedback from the detector tube of a regenerative receiver to the loop, increasing the Q. Before World War 2 most medium wave (AM) radios used air-core loop antennas, which had to be large to bring in distant stations. The invention of high permeability ferrite cores allows the loop antennas used in modern AM radios, called ferrite loopsticks, to be much smaller, and be enclosed inside the radio's case. This antenna was called the Aero-Loop, manufactured by Utt-Williams Electrical Products Co. and distributed by Scott Sales Co. and sold for $12.50.