The first wireless transmissions, including those of Marconi, employed spark technology. Everyone knows the effect of switching a light on or off when an AM radio receiver is in the room; the spark in the switch causes radio wave energy that the radio picks up – regardless of the frequency the receiver is tuned to. The spark transmitter did the same thing, though with a modicum of tuning. Not enough, however, to enable the use of spark transmitter today as it would cause interference across many frequency bands.


To create a spark you needed a large voltage difference - the bigger the voltage difference, the bigger the spark. There were no valves to amplify the signal so the bigger the spark, the more radio energy created. The more radio energy created, the further you could transmit a signal.  However another early experimenter, Fessenden, recognised that continuous wave (CW) transmission was required for speech, and he felt that he could better transmit and receive Morse code and voice by the CW method. Fessenden was right and actually transmitted voice and music as early as 1906, but "King Spark" was slow to die. Eventually though, the Marconi spark transmitter was replaced by the CW system, which in turn was replaced by vacuum tube (valve) transmitters.


By 1924 spark was banned except as a back-up for distress messages on the international distress frequency of 500 kHz (600 metres). By the end of WW 2 spark was all but forgotten.


          Text supplied by Wayne Wedderspoon.