THE TELEGRAPH ANCILLARY

See also
E.I. Telegraphs, General H1001 - Ancillary equipment description.
E.I. Telegraphs, General H1003 - Ancillary features and circuit description.

An extract from the
Post Office Electric Engineers Journal
Volume 29 - July 1936

The Telegraph Ancillary

The authors describe a new telegraph switchboard, on which the lines at a large office are multipled to enable any teleprinter to be connected to any line in accordance with traffic requirements.

Introduction
During the ten years or so prior to the reintroduction of the sixpenny telegram, telegraph traffic had shown a progressive decline, and, as a consequence, the telegraph network of the country had been proportionately reduced. Many long distance circuits were withdrawn, since the, amount of traffic did not justify their continuance, and minor local circuits were converted to telephone methods of working. It was difficult however to absorb all the redundant terminal equipment and staff and overhead charges remained substantially unchanged.

The introduction of the multi-channel voice frequency telegraph system in 1931, together with the conversion from Morse and Baudot to teleprinter working, considerably reduced the engineering costs of the provision of telegraph circuits.

The expansion of traffic following the reduction of charges in 1935 led to the desirability of converting a large number of telephone-telegram circuits to teleprinter working, as by this means traffic can be disposed of more rapidly. These circuits, however, will only be called upon to carry a relatively small load, and in a large percentage of cases the amount of traffic does not justify continuous staffing and the provision of separate apparatus.

When a number of such circuits radiate from a single transmitting centre, an advantage results from connecting the lines to a switchboard instead of appropriating a separate teleprinter to each line. Such a switchboard provides a means of connecting any line to an operating position when a message has to be sent or received, and under such conditions a considerable economy in teleprinters and office space can be effected. This method of working has the further advantage that the operators are relieved of the necessity of keeping a watch on several instruments, and of moving about from one to another.

To meet these needs a system of ancillary working has been devised, the operation of which may be regarded as being similar in principle to that of an ordinary telephone switchboard. The number of operating positions and the number of lines to which access is given are dependent upon the size of the telegraph office concerned and the busy hour traffic load.

To meet the traffic and engineering requirements, the system embodies the following facilities:-

1. Permits the concentration of all types of circuits, viz., V.F., two line simplex and duplex circuits.

2. Gives full availability to all circuits at any operating position for both incoming and outgoing traffic.

3. Includes an automatic distribution indicator.

4. Provides metering for traffic recording purposes.

5. Provides facilities for the rapid transfer of circuits to reserve positions during busy periods.

Circuit Requirements
It should be mentioned that in most large telegraph offices all apparatus apart from the teleprinter has been removed from the instrument table and, in the case of physical circuits, this apparatus has been fitted on rack mounted panels, the local extensions being connected to the instrument table via a concentrator board. Consequently, from this board to the instrument table all types of circuits conform to a uniform standard as regards wiring and operation, i.e., simple direct current sending and receiving local circuits, and this point was found to be the most suitable at which to introduce the ancillary apparatus.

The normal condition of a circuit with the distant station teleprinter at rest is negative current to line (in the case of V.F. circuits to the SEND relay) and negative current from the relay to the teleprinter at the receiving end. A calling relay, upon the operation of which all subsequent functions of the associated apparatus will depend, must therefore be introduced. This relay should be inoperative to a negative current, but should operate on a momentary reversal of current by the operation of any teleprinter key at the out-station.

This condition is obtained by using a telephone relay shunted by a rectifier to operate first on a positive impulse and then to be held operated by a locking circuit (see Fig. 1).

FIG. 1 - CIRCUIT OF CALLING RELAY

Equipment
The essential equipment of an ancillary system comprises:-

1. A suite of operating positions each fitted with a teleprinter and a small panel (Switchboard, Teleprinter No. 1, Fig. 2) on which circuit jacks and signalling lamps are accommodated and which also affords various facilities which will be described later. The maximum capacity of this panel is 60 lines.

2. A distribution position with a panel (Switchboard, Teleprinter No. 2, Fig. 3) indicating engaged circuits and positions.

3. A transfer panel (Switchboard, Teleprinter No. 3, Fig. 4) providing for the transfer of circuits to adjacent reserve positions, synchroscope tests for checking the speeds of out-station teleprinters, and bunching of circuits for the simultaneous transmission of the TIME signal.

4. A number of reserve positions terminated on jacks on the transfer panel.

5. Rack Equipment (Equipment, Ancillary TG 970). The apparatus associated with the ancillary is mounted on panels fitted on standard telegraph racks (see Fig. 5). The jack-in principle has been adopted for the line equipment, i.e., the calling and engaged relays together with the flashing relays are mounted in a small unit on a telegraph relay base so as to jack into a Baseboard No. 26 (Fig. 6). These units are mounted on both sides of the rack.
   On the front of the rack, above the line relay sets, are mounted three panels. The first carries the 14 "position" relays, the second the meters, and the third the delayed call flashing equipment and the pulsing relays for metering purposes.

6. Power equipment. This is also rack mounted and provides the necessary fuses and transformers for the 6 v. A.C. supplies for the lamps.

Teleprinter Switchboard
To enable the sequence of operations associated with a call to be followed it is desirable to describe the operator's switchboard. This is shown in Fig. 2. On it are mounted a labelled jack, a white calling lamp and a red engaged lamp associated with each circuit.

Below the jack and lamp field is a key and jack strip accommodating two keys, (the "position-staffed" key and the "reset" key), two jacks for TIME and local test and two lamps (the white "circuit-hold" and red "duplicate-connexion" lamp). On the top of the switchboard is a unit containing two lamps, one a green lamp indicating that the position is staffed and the other a red lamp indicating that the position is busy. These lamps are brought into use by the operation of the "position-staffed" key when the position is opened for traffic purposes.

The teleprinter "Send" and "Receive" leads are connected to a plug and cord attached to the switchboard, and the instrument can be connected to any circuit by plugging into the corresponding jack.

The line circuits are connected from the concentrator and are multipled on all the switchboards.

FIG. 2 - OPERATORS' SWITCHBOARD

FIG. 3 - DISTRIBUTION BOARD

Operating Procedure
An incoming call on the ancillary equipment causes the calling lamp associated with the circuit to glow at every position. If the call is not answered within a period varying between 24 and 60 seconds this glow changes to a flash. During this calling period the "Send" and "Receive" lines are looped via the calling relay (L); consequently the calling station receives its own signals back as an indication that the call is awaiting attention.

The call is answered when any operator plugs into the associated line jack; this extinguishes the calling lamp and causes the engaged lamp on every position and on the distribution panel to glow. At the conclusion of the call the plug is withdrawn and the circuit restores to normal.

A connexion for outgoing traffic is made by plugging into the jack of the required circuit. This lights the engaged lamps as on an incoming call.
 

FIG. 4 - TRANSFER BOARD

FIG. 5 - RACK EQUIPMENT AND FUSE BOARD (TG 970)

In order to eliminate ineffective operating time due to calling the out-station and awaiting acknowledgments, the teleprinters have, been fitted with an "answer-back" device. On plugging into :the jack of the required circuit the operator depresses a "who-are-you? " key on the. teleprinter and the signal transmitted by this key actuates the "answer-back" unit on the out-station teleprinter. The unit automatically transmits the code of the called office and this is accepted as an indication by the calling operator that the distant teleprinter is functioning correctly. The message or messages are transmitted forthwith without waiting for any further instruction or signal to proceed, and on completion of the transmission the "who-are-you?" key is again depressed. This time the reception of the code of the distant office is regarded as an indication that the distant teleprinter has functioned satisfactorily during the transmission and is accepted as an acknowledgment that, the message or messages have been received.
 

FIG. 6 - LINE RELAY SET (TG968)

The Duplicate Connexion Alarm Unit
To prevent duplicate reception of messages due to two or more operators answering the same call, a duplicate connexion alarm unit has been fitted in each switchboard. This unit, consisting of two relays and a rectifier, is inserted in the teleprinter cord circuit; its operation is shown in Fig. 7.

When a double connexion has been made, the 80 v. negative transmitting battery is connected to tine via parallel paths, the current in each path being approximately 20mA. and insufficient to operate relay A. On the reversal of battery at one position, i.e., when the operator transmits the "G" signal, the positive battery on that position is momentarily connected through the line jacks to the negative battery on the other position. The current in the cord circuits rises to approximately 600mA. and the direction of this current is such that relay A and in turn relay B of the second operator's unit only are operated. The second teleprinter is disconnected from the line to prevent interference with traffic, and the lamp indicates that a duplicate connexion has been made. On receipt of this indication the second operator withdraws the teleprinter plug from the line jack and extinguishes the lamp by operating the reset key.

Distribution of Traffic
In order to expedite the distribution of outgoing traffic and to retain engaged circuits for which further traffic has been received, a distribution indicator panel has been incorporated. This panel (see Fig. 3) is similar in size and appearance to the operator's switchboard and is located at the traffic circulation drop-point. It is fitted with engaged lamps and keys associated with each circuit on the ancillary, the lamp being operated in conjunction with the engaged lamps on the operator's switchboards. Above this lamp and key field are position lamps corresponding to the ancillary and reserve positions. On receipt of a message for an engaged circuit the distribution operator depresses the key associated with the line; this causes a lamp to glow to indicate the operator's position to which the required circuit is connected. At the same time the "circuit hold" lamp on the operator's switchboard glows to indicate that the circuit should be retained for further traffic. This lamp is extinguished by the operation of the reset key.

Reserve Positions
During the peak traffic hours congestion on the ancillary positions may necessitate the transfer of certain busy circuits to reserve positions, and in order to effect this transfer quickly, and at the same time retain the distribution indicator facility, a transfer panel has been designed (see Fig. 4). The reserve positions are connected to jacks on the transfer panel, and associated with each circuit are a key and line jack. By operating the key to "Reserve" and connecting the line jack and a position jack with a double-ended cord the circuit is transferred to a reserve position. The engaged lamp on the distribution panel glows and the indicator facility is obtained in a similar manner to that obtained with the ancillary position.

This panel is used also for the bunching of circuits for the simultaneous transmission of the time signal. By operating the keys to TIME, the "send" lines of a number of circuits are connected to a time-jack on the operator's switchboard and all engaged lamps associated with the bunched circuits are made to glow.

Facilities have also been provided to connect any out-station teleprinter to the synchroscope for speed check purposes.

A system of metering has been incorporated for traffic recording, One set of meters recording the number of connexions per position, while a second set of meters gives the aggregate duration of operating time per position. These meters are controlled by a master key and are brought into operation as required.

Outline of Circuit Operation (see Fig. 8)
It has been previously explained that the operation of the ancillary equipment is dependent upon the calling relay (relay L) which operates on the first depression of a teleprinter key at the out-station, and then locks. This relay lights the calling lamps, and also starts the delayed call flashing equipment, which is controlled by the successive operation of relays FA and FL at an interval of approximately 30 seconds. The time interval between the operation of these relays is controlled by means of a uniselector, stepping once every six seconds.

When any operator plugs into the calling circuit, relay E in the sleeve circuit operates and disconnects relay L. It also lights the engaged lamps on the operators' switchboards and the distribution panel. At the same time relay PE in the sleeve circuit of the operator's position will operate to change the green lamp on the top of the switchboard to red. This relay also controls the metering circuit.

The distribution facility is provided by inserting a resistance in the sleeve circuit which can be short-circuited by means of the press-button key at the distribution board. At the same time the operation of relay DA removes the short circuit from the H relays associated with each position, and the H relay in the sleeve circuit in which the resistance has been short-circuited will operate. This lights the corresponding position lamp on the distribution board, and also operates relay PH which lights the "circuit-hold" lamp at the operator's position.
 

FIG. 8 - FUNDAMENTAL CIRCUIT CONDITIONS
 

When the plug is withdrawn from the multiple, relays E and PE restore, and the circuit is restored to normal.

Conclusion
Experimental ancillary systems were installed :at Bristol, Birmingham, Newcastle and Glasgow in July, 1935, and handled the summer peak traffic at these offices. A typical ancillary suite is shown in Fig. 9. Further equipments will be installed at most of the Telegraph zone centres during the present year.

FIG. 9 - GENERAL VIEW OF ANCILLARY (CTO)

Last revised: September 02, 2023