Lodge's experiment: Spark gap radio transmitter and receiver.

Lodge's experiment: Spark gap radio transmitter and receiver. This is a primitive radio experiment, performed by Oliver Lodge in the 1890's. The transmitter consists of a Leyden Jar, a spark gap, and a tuneable loop of metal. The Van de Graaff generator (or high-voltage D.C. generator) charges up the Leyden Jar. At some point the voltage is high enough so that a spark jumps the 1/4" air gap. The Leyden Jar is a capacitor, and the loop is an inductor,-so the basic circuit is a parallel LC tank circuit that oscillates at a certain frequency (in this case about 2.5 MHz). The receiver consists of a Leyden Jar, a loop, and a neon tube. The receiver is placed about a foot from the transmitter. When the transmitter is regularly sparking, radio wave pulses are picked up by the receiver most strongly when the moveable vertical bar of metal on the transmitter loop is moved to the 'resonant' position. At this point, the neon bulb on the receiver flashes with each spark of the transmitter. The capacitance of the Leyden Jar is about 2.6 nf. The inductance of the loop is about 1.6 micro H. Each spark oscillates at about 2.5 MHz and rapidly decays in about 6 microseconds. The wavelength is about 120 M. See: 'Modern Views of Electricity' by Oliver J. Lodge, 2nd Edition, 1892, in Bechtel Library QC 518.L6
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