English: An inductor (tank coil) from the tuned circuit of an RF power amplifier of a shortwave radio transmitter, from an advertisement in a 1938 radio magazine. The promotional copy said it was usable up to 27 MHz. This inductor illustrates high Q construction used to reduce resistive losses at high frequencies; it is made of a single layer winding with the turns spaced apart to reduce proximity effect losses, the wire is thick and silver plated to reduce skin effect losses, and the coil is not wound on a coil form but is supported by thin plastic insulators to reduce dielectric losses. It is a plugin unit so the frequency of the transmitter can be changed by exchanging it with a different coil.