ERICSSON TELEPHONE No's N20653 & N20649


INTRINSICALLY SAFE 'MINE RESCUE' TELEPHONE
BATTERY RINGING
Certificate: T/TEL/78 (Methane)

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N20653 N20649
Advance Station Unit Base Station Unit

This apparatus has been specially designed in collaboration with the Ministry of Fuel and Power, and Rescue Station Superintendents, so that when an accident occurs in a mine the rescue party shall be provided with a safe and reliable system of communication.

The Base Station Unit N20649 comprises a silicon-aluminium case containing a transmitter, loud-speaking receiver, buzzer, speaking key, ringing key, plug socket and under the flap on the left a buzzer test key and adjustment screws.

The Advance Station Unit N20653 is also constructed in silicon-aluminium and is similarly-equipped, but in addition a special cable reel is incorporated for paying-out the line wires as the rescue party advances. A transmitter is not fitted in this unit, as speech is not practicable, since respirators are usually worn by the rescue party. The cable reel holds approximately 280 yards of a specially strong cable. The unit is fitted with a robust carrying strap and a collapsible reel-handle.

Communication is maintained uninterrupted during paying-out and reeling-in of the cable.

If, during rescue operations, it is desired to extend beyond the first cable length, a second advance party instrument can be connected by a simple plug, and the circuit transferred from the first to the second unit.

The facilities for communication are as follows

The base party can speak, or code signal by buzzer and key, to the advance party.

The advance party can receive speech and code signals and send code signals to the base party.

Standard cycle-type dry batteries of 3 and 6 volts are provided for the advance and base station, respectively, thus, in emergency, replacements can be readily obtained from any cycle or electrical dealer.

The internal wires are insulated with p.v.c.

Taken from the Ericsson catalogue No. 60

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Last revised: June 20, 2003