An antenna variometer a variable inductor used to tune a transmitting radio antenna to resonance with its transmission line to avoid standing waves, from an ad in a 1945 magazine. It consists of two inductors connected in series; a large stationary one consisting of 4 turns of copper tubing, and a smaller one inside it consisting of two turns, that can be rotated on a horizontal axle by a handle. Rotating the inner inductor so its magnetic axis is at an angle to the outer one allows the inductance to be varied continuously, from a high value when the two coils are parallel with their magnetic fields in the same direction, to zero when the inner coil has been rotated 180 deg so its magnetic field opposes that of the outer coil. Radio frequency current travels only on the surface of conductors due to skin effect, so the coils are made of large diameter tubing with a large surface area to reduce the resistance. The coils are made self-supporting with a minimum of insulating supports to reduce dielectric losses. Alterations to image: blocked out advertising copy overlying image in lower left corner.