A hundred years ago this month, the April 1920 issue of Popular Science carried this ad for an induction coil and spark gap said to have a range of 25 miles using direct current. The induction coil, which consisted of a vibrator, primary winding, and secondary winding, would produce a high voltage alternating current using a 6 volt storage battery. This was fed to the quenched gap, which produced the spark to be radiated by the antenna. Together, the two components were the heart of the transmitter. The induction coil was also available in a 32 volt version for use on farm lighting circuits of that voltage. This setup was promised to make other amateurs in your state sit up and take notice when your signal showed up in the ether.

The two components were available together for $33.50. It was recommended to buy the set from your local dealer, but if none was available, the American Radio and Research Corporation would send it for five dollars down, with the balance plus postage paid C.O.D.

Since the set used high-quality surplus Signal Corps parts, only a limited number of sets could be made.

The ad showed the company has having its factory at Medford Hillside, Mass., with offices at 29 Park Row, New York.