Long-wave radio telephone-telegraph transmitters

A description of two transmitters covering a wave range of from 600 to 3600 metres, the powers being about 1.5 kW and 3.5 kW. The transmitters are master-oscillator controlled with provision for modulation for telephony. They are built in three units, an input unit containing the master oscillator and speech amplifier and keying circuits, an amplifier unit housing the modulator and power amplifier valves, and, finally, an aerial tuning unit which contains the output circuit and aerial tuning arrangements. The input unit is common to both transmitter powers, but while the 1.5-kW power amplifier has air-cooled valves, the 3.5-kW one has water-cooled valves. An ingenious from of key is used consisting of two iron cylindrical armatures housed in an evacuated glass tube and held apart by two stiff helical springs. This tube is merely slipped inside a suitable winding, the energisation of which causes the armatures to move into contact. Connection is made to the armatures by flexible leads brought out through the glass tube by seals. The article includes a circuit schematic and five illustrations.