Telegraph sounder used for the reception of telegraph messages transmitted by Morse code.
Telegraph signals were transmitted by an operator who depressd a key to complete an electric circuit and transmit current along the telegraph line. Releasing the key broke the circuit and cut off the current. Letters and numbers were represented by a sequence of short current pulses ('dots') and long current pulses ('dashes'), transmitted according to a defined code. The most widely used code was generally known as "Morse code".
At the receiving end of the telegraph line, the incoming current pulses passed to the receiving instrument, or 'sounder'. Two horizontal wire coils were energised by the received pulses, causing the metal arm across the ends of the coils to move to and fro. The movement of the arm could be heard as a succession of metallic clicks. The interval between the clicks was short in response to the short current pulse representing a 'dot', or long in response to the long current pulse representing 'dash'. A skilled operator could interpret the succession of clicks as a pattern of dots and dashes and immediately decode the letters and numbers in the received message.
Two horizontal wire coils on vertical wooden support, attached to wooden base. Brass components. All enclosed by wooden cover with glass top. Cover held in place by two 'hook and eye' catches.
Top of wooden coil support inscribed in white: "A (Crown symbol) M REF. No. 5B/117" Top wooden coil support also marked in black: "R JUL 1942" and: "A.I.D 94. V." inside a rectangle.
Type of item
175 mm (Length), 168 mm (Width), 132 mm (Height)