English: Very early directional spark radio transmitter and receiver used by Guglielmo Marconi in his first historic experiments in radio communication in 1895. The transmitter (left) consists of a Righi spark gap powered by an induction coil (not visible) connected between the arms of a short dipole antenna at the focal line of a cylindrical sheet metal parabolic reflector to concentrate the radio waves into a beam. The transmitter and receiver dishes were pointed at each other. The receiver (right) consists of a similar parabolic reflector and dipole antenna, connected to a coherer, a primitive radio wave detector consisting of a glass tube with two electrodes with metal powder between them. Sparks across the spark gap in the transmitter created radio waves which were focused into a beam by the reflector aimed at the receiver. At the receiver the radio waves picked up by the dipole antenna caused the metal powder in the tube to "cohere" (clump together), causing the coherer to conduct electricity. Current from a battery flowed through the coherer, ringing a bell.

The frequency of radio waves produced would have been in the UHF range, several hundred megahertz, roughly the frequency now used by television stations. Marconi found that using parabolic antennas increased the transmission distance greatly compared to his earlier plain dipole antennas.

Caption of left image: This picture shows a very early model transmitter, invented by Marconi for short-wave beam-radio work.
Caption of right image: Marconi's early model receiver for focusing the signals from beam trasmission, designed by him in 1895.

Alterations to image: combined two separate images from source page.