Calling system
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A twin-tone selective calling system made by Pye Telecommunications Ltd. for large fleets of vehicles using radio' telephones has been designed to eliminate continuous receiver monitoring. Operators of large fleets can contact one or more units without alerting the remainder.
The system consists of a control station and mobile encoding and decoding units. It uses 18 tone frequencies to provide up to 123 codes for the control station to call vehicles. Each radio telephone can have up to 10 codes for control station calling.
Code selection is by two banks of press buttons, the code being transmitted automatically when the appropriate button is pressed. A separate button provides for group calling.
Facilities are also available for the operation of an external warning device such as a flashing light.
Made by: Pye of Cambridge Ltd., Cambridge.