One of the more powerful arc transmitters constructed were the 1,000 watt units built for the U. By gradually scaling up the equipment Federal Telegraph finally produced a 30 k W unit that outperformed a powerful rotary spark transmitter at the Navy's Arlington station.
The navy wanted still more power and Elwell thought he could build a 60 k W unit by merely scaling up the parts again. Arc transmitters were gradually eliminated when the new vacuum tube transmitters came into use. Perhaps the last to be in operation on land were the stations operated by the Mackay Radio and Telegraph Company between cities on the Pacific coast.
A synchronous rotary had the spark electrodes mounted on the shaft of the motor generator which feeds a HV step up transformer.
In this way, the spark would discharge the capacitor synchronously with the peak in the AC waveform.
They were complicated to operate and were infamous for exploding when an operator introduced too much alcohol into the chamber.
At the conclusion of the battle, he returns to Athens, where he reportedly shouted Rejoice! The operating procedures, codes and protocols of the telegraph were carried over to the new age of "wireless".His transatlantic triumph came on the 12th December 1901 when the morse letter 'S' was transmitted from Poldhu, in Cornwall and received by Marconi himself at St.John's, Newfoundland, who recorded the historic event in his pocket book simply "Sigs at 12.20, 1.10 & 2.20".By adding a resonant circuit to the arc it would oscillate at a frequency determined by the LC constants.Duddell's arc would only oscillate at audio frequencies, audible to human hearing, and it was dubbed the "singing arc."In 1902 Valdemar Poulsen, succeeded in making the arc oscillate at the higher frequencies by using electrodes operating in a sealed chamber, with hydrocarbon vapor, and a strong magnetic field.Spark transmitters were often placed in acoustically insulated rooms to deaden the sound.