Standard short-wave radio transmitters
01 February 1930
This paper describes the type 3 short-wave transmitter designed by the International Telephone and Telegraph Laboratories Inc., which is used on the Madrid-Buenos Aires Radio Link. It operates within the wave-length range of 15 to 60 m. and can deliver to the aerial a maximum power of 12 kW on continuous wave telegraphy or about 3kW on telephony with 100% linear modulation. For commercial speech operation a certain measure of distortion is permissible and the carrier power may be raised to about 4.6 kW. The transmitter, which is quartz controlled, is built on the unit principle. The first unit contains the quartz oscillator, frequency doubling valves, speech amplifier, keying arrangements and modulating equipment, the final output being two 250-watt valves in push-pull. The intermediate amplifier which forms the second unit has two 2-kW water-cooled valves in push-pull. The final power amplifier which forms the third unit has two 10-kW water-cooled valves. Each of the three units has a separate power panel provided for it to control the generators which it needs. Simplified schematic circuit diagrams are given of the complete transmitter and its various components.