A. S. Popov Central Museum of Communications, St. Petersburg 1978
Transmitter: 35 x 16.5 x 22 cm, ca. 3 kg; receiver: 36 x 26 x 21 cm, ca. 4 kg
Radio transmitter (Ruhmkorff coil, blocking capacitor), receiver (coherer, amplifier, electric bell, aerial)

This wireless transmission system consists of a radio transmitter (Ruhmkorff coil) and a receiver with coherer to register electromagnetic oscillations made audible by a sequence of sounds on an electric bell. If the transmitter button is pressed briefly, the receiver replies with a single ring, while if the key is held down, the receiver produces a series of rings. The coherer must be shaken to resensitize it, which happens automatically when the bell hammer taps the bell.