85 MHz radio transmitter, with indicating lamp on dipole antenna.

85 MHz radio transmitter, with indicating lamp on dipole antenna. This is a simple radio transmitter and receiver demonstration apparatus. The transmitter is a high frequency vacuum tube oscillator with a fixed frequency of 85 MHz (3.5 M wavelength), powered by a transformer. Mica capacitors are mounted within the bakelite case, and the simple loop (7 cm. diameter) on top is the inductance. Horizontal copper 'sending' antennas are plugged into the ends of the inductance loop. The first receiver is a simple linear oscillator which is a straight copper conductor connected at its middle through a small incandescent (or neon) lamp. Its length can be adjusted by means of copper rods telescoping into its ends. When the length is properly adjusted so that it oscillates at the frequency of the transmitter, the lamp glows brilliantly within a meter of the transmitter, and continues to glow at several meters. The second type of receiver ('wavemeter')consists of an inductance loop, and a variable capacitor. The receiver can be tuned from 3 to 5 meters wavelength, lighting the pilot lamp.