Cyclopedia of Telephony and Telegraphy, Vol. 2 Informative Summary

Overview:

This text provides a detailed exploration of the technology and practices surrounding telephony and telegraphy in 1919. It delves into the workings of both manual and automatic systems, comparing their advantages and disadvantages. The book emphasizes the transition from magneto to common-battery systems, highlighting the benefits of centralized power and automated signaling.

The authors provide comprehensive explanations of multiple switchboard operation, including the busy test and its potential shortcomings. They also explore the development of different types of relays and jacks, essential components of these systems.

In addition to telephony, the text covers telegraphy and its applications in railway operations. It examines the use of phantom, simplex, and composite circuits, which allow for multiple communication channels over the same set of wires.

Key Findings:

Common-battery systems offered significant advantages over magneto systems in terms of maintenance, signaling, and overall efficiency.
Multiple switchboards were essential for handling large-scale telephone traffic, but required careful design to prevent double connections and ensure accurate busy tests.
Automatic systems, despite their complexity, offered greater efficiency and flexibility compared to manual systems, particularly for handling large-scale traffic.
Telephone train dispatching, a relatively new application at the time, proved to be faster, more efficient, and offered greater safety compared to traditional telegraph systems.

Learning:

Understanding the differences between manual and automatic telephone systems: The reader will learn about the key components and operating principles of both types of systems, gaining insight into their advantages, disadvantages, and areas of application.
Exploring the complexities of multiple switchboards: The text explains how multiple jacks, relays, and signal circuits are interconnected and function to establish and supervise telephone calls.
Learning about the evolution of telephony: The reader will gain an understanding of how the technology progressed from magneto systems to common-battery systems, with the introduction of automatic signaling and more sophisticated switching mechanisms.
Understanding the challenges of telephone traffic: The text provides detailed explanations of the variations in telephone traffic, the importance of traffic studies, and the methods employed for analyzing and managing it.
Exploring the applications of telephony beyond basic communication: The reader will learn about the use of telephony in train dispatching, private branch exchanges, and other specialized areas.

Historical Context:

This text was written in 1919, a time of significant growth and development in the field of telephony. The world was still recovering from the First World War, and the demand for faster and more efficient communication systems was increasing. The widespread adoption of common-battery systems and the emergence of automatic telephone systems reflected the technological advancements of the era.

Facts:

Common-battery systems simplified subscribers’ instruments: By eliminating the need for local batteries and magneto generators, common-battery systems reduced maintenance requirements and made telephone service more convenient for subscribers.
Magneto systems were preferred in rural areas with long lines: The lack of readily available power for charging batteries made magneto systems a more practical choice in rural communities.
Pilot lamps are used to alert operators to incoming calls: These lamps, located on the switchboard, signal the operator that a call is waiting, allowing them to quickly locate the specific line.
Supervisory signals are used to monitor the status of calls: These signals, usually in the form of lamps, alert the operator when a subscriber hangs up their receiver, indicating the need to disconnect the call.
Early multiple switchboards were magneto-based: As common-battery systems evolved, they gradually replaced magneto systems in larger exchanges.
The busy test is crucial in multiple switchboards to prevent double connections: This feature ensures that a single line can’t be connected to multiple callers at the same time, avoiding confusion and service disruptions.
The cut-off relay simplifies jack design in common-battery multiple switchboards: By disconnecting the line relay when a call is answered, the cut-off relay allows for the use of smaller, less complex jacks.
The two-wire system eliminates the need for a ground connection at the subscriber’s station: This feature simplifies the subscriber’s telephone and improves the reliability of the system.
Automatic systems have proven to be adaptable to various service types: Initial concerns that automatic systems were inflexible have been proven unfounded as they have successfully implemented party-line ringing, reverting calls, and integration with manual systems.
The public has generally accepted the need to dial their own calls in automatic systems: Concerns that subscribers would find automatic systems inconvenient have been proven false as users have adjusted to the dialing process.
The Strowger system, invented by Almon B. Strowger, is the most widely used automatic system: The Strowger system, developed and refined by the Automatic Electric Company, is characterized by its step-by-step switching mechanism controlled by impulses from the subscriber’s dial.
The Lorimer system is an automatic system that uses power-driven switches: Invented by the Lorimer brothers, this system utilizes a mechanical approach to switching, with electrical impulses controlling the operation of power-driven switches.
The line switch is a key component in automatic systems, reducing the need for first selectors: This device, one for each subscriber line, connects the line to an available first selector trunk, thereby optimizing the use of selectors based on traffic demand.
The master switch in automatic systems keeps plungers pointing to idle trunks: This mechanism ensures that the next available trunk is ready for selection when a call is initiated.
The bridge cut-off relay in the line switch disconnects operating magnets after they have served their purpose: This feature ensures that these magnets are not constantly drawing power, saving energy and improving efficiency.
Private branch exchanges (PBX) provide local communication within a business and connections to the public network: These systems are typically manually operated, with an operator handling calls within the business and connecting them to the external network.
Private branch exchanges can integrate with both manual and automatic public networks: They offer flexibility in meeting the communication needs of various businesses.
Intercommunicating systems allow direct communication between stations without an operator: These systems, limited to smaller installations, provide direct connections between stations, eliminating the need for a central switchboard.
Phantom circuits create additional telephone lines over existing wire pairs: By utilizing repeating coils and transpositions, phantom circuits increase the capacity of existing cable runs.
Simplex circuits allow for simultaneous telephone and telegraph communication over a single line: Using impedance coils and condensers, these circuits enable the transmission of telegraph signals without interfering with telephone conversations.

Statistics:

Automatic systems can handle traffic from 1,000 calls per hour per operator: The automanual system, for instance, demonstrated the ability to handle calls at a rate exceeding 1,000 per hour per operator.
Subscribers’ waiting time in automanual systems averaged 2.07 seconds: This statistic showcases the efficiency of this system in responding to calls.
Storage batteries in telephone exchanges can provide 24 hours of service after a full charge: This ensures continued operation even in the event of a power outage.
A large storage battery cell can have a capacity of 4,000 ampere hours: The size and capacity of battery cells are determined by the number and area of lead plates.
The busy-hour traffic in large cities constitutes about one-eighth of the total daily calls: This statistic highlights the concentration of telephone usage during peak hours.
The trunking factor, representing the ratio of actual to theoretical out-trunking, is typically 75%: This indicates that more local calls are handled within an office than initially predicted.
A single trunk in a manual system can handle 7 to 15 conversations per busy hour: The number of conversations a trunk can handle depends on the number of trunks in a group.
A single trunk in an automatic system can handle 15 to 34 conversations per busy hour: Automatic systems generally offer higher trunk efficiencies due to factors such as quicker answering and shorter conversations.
A long-distance trunk can handle 2 to 4.6 conversations per busy hour: The capacity of long-distance trunks also varies based on the group size.
The average time of a local conversation is 100 seconds: This statistic provides insight into the duration of local telephone calls.
Telephone train dispatching circuits can extend for up to 300 miles and serve up to 65 stations: This reflects the vast distances and complexities of this specialized application of telephony.
A telephone train dispatching circuit can handle calls at a rate of 10 per second: This demonstrates the efficiency and speed of the selector system used in these circuits.
The typical voltage of a sending battery for train dispatching circuits ranges from 100 to 300 volts: The voltage is determined by the length of the line and the number of stations.

Terms:

Common-battery system: A telephone system that supplies direct current from a centralized battery at the central office for powering subscribers’ instruments and operating signals.
Magneto system: A telephone system that relies on a magneto generator at each subscriber’s station to produce ringing current and a local battery for powering the transmitter.
Multiple switchboard: A type of telephone switchboard that allows each operator to connect to any subscriber line in the exchange without the need for assistance from other operators.
Answering jack: A specialized jack on a switchboard that allows the operator to answer an incoming call from a specific subscriber line.
Multiple jack: A jack on a switchboard that provides a connection point for any operator to access a specific subscriber line.
Busy test: A feature in multiple switchboards that ensures that a single line cannot be connected to multiple callers simultaneously.
Cut-off relay: A relay that disconnects the line relay from the line when a call is answered, simplifying jack design.
Line switch: A device in automatic systems that connects a subscriber line to an available first selector trunk, efficiently directing calls to the appropriate switching equipment.
Intercommunicating system: A specialized telephone system where each station is connected directly to every other station, allowing subscribers to communicate directly without an operator.
Phantom circuit: An arrangement of telephone wires that allows for more communication channels than the number of physical wire pairs.

Examples:

The iron-wire ballast: This device, placed in series with a line lamp, helps to regulate the current flow to the lamp, ensuring proper illumination regardless of the line’s resistance.
The plug-seat switch: This device, operated by the insertion or removal of a plug, can be used for switching or signaling purposes in telephone systems.
The Sabin-Hampton system: A large-scale transfer system that once served thousands of lines in San Francisco, but was later replaced by multiple switchboards.
The Divided Multiple switchboard: An early attempt at increasing the capacity of multiple switchboards by dividing the multiple into sections, which was later abandoned in favor of smaller, more efficient boards.
The trunk repeater: This device in automatic systems allows for inter-office trunking over two-wire lines, enabling communication between offices without the need for a separate third wire.
The rotary connector: A special type of connector in automatic systems that can automatically select an idle trunk from a group of lines, ensuring that a call is not missed due to busy lines.
The Lorimer automatic system: An automatic system that uses power-driven switches controlled by electrical impulses, providing an alternative to the more widely used Strowger system.
The automanual system: A hybrid system that combines features of manual and automatic systems, automating the switching process while retaining the role of an operator for call handling.
The Warner pole changer: A device that converts direct current into alternating current, commonly used for ringing bells in telephone systems.
The mercury-arc rectifier: A device that transforms alternating current into direct current, providing an efficient and reliable means for charging batteries in telephone power plants.

Conclusion:

This text offers a valuable historical snapshot of telephony and telegraphy in 1919, demonstrating the rapid evolution of these technologies and their growing significance in communication and transportation. It explores the transition from manually operated systems to more efficient automated systems, highlighting the challenges and triumphs of this technological shift.

The text’s detailed descriptions of different telephone systems, power plants, and specialized applications provide readers with a thorough understanding of the principles and practices of telephony and telegraphy at the time. It is a fascinating and informative resource for anyone interested in the history of communication technology.

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