TRAFFIC CONTROL TELEPHONE SYSTEMS Circuit - Sam Hallas

Page 6
Retard Coils No. V.4400-6
These coils, together with their associated capacitors, smooth out the impulses
of current during signalling, so that the code is heard in the Controller's receiver as
slight dull thumps, and not as objectionable sharp clicks.
This network also tunes the circuit so that with average line conditions the
transmitted wave form is practically sinusoidal.
Way Station Selectors 4304-A & 4301-A
The selector is the receiver of the system and will only operate its associated
call bell on receipt of its own particular code, general call code or time signal code.
It is fully described in Part 3, and this should be read in conjunction with the
circuit description below.
Way Station Selector Set 4001-A
The Way Station Selector Set contains the selector with its tuning capacitors,
ring back tone capacitors, and local battery bell. With this type a separate telephone
set is used but Selector Sets containing both selector and telephone circuits are also
supplied.
Way Station Telephone Set
This can be either a wall or desk set. The "Speak-Listen" switch takes the form
of either a key fitted in the wall set or a foot switch connected to the desk set.
Battery Supplies
At the Control
At each Way Station
APPARATUS USED ON A TYPICAL KEY SENDING
TRAFFIC CONTROL SYSTEM
At Control Station
Local Battery : 10 volts for operating the relays.
Line Battery : The voltage is dependent on the length
of line and the number of way stations employed.
(See the Line-Voltage curves, Part 6.)
3-volt battery for talking and ringing.
One No. 4001-C Selector Apparatus Case.
One No. 4002-A Selector Key Case (capacity twenty Selector Keys) to accommodate
first twenty selector keys.