Telephone Systems Quiz

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Questions and Answers

What is the duration of the make pulse in pulse dialing?

39 ms (correct)

50 ms

61 ms

100 ms

Which condition indicates that a telephone set is off-hook?

The ringer is connected to the central office

The line requires at least 23 mA of current (correct)

The handset is placed back in the cradle

Only AC current flows in the line

What type of dialing uses two frequencies to send a telephone number?

Pulse Dialing

Analog Dialing

Touch Tone Dialing (correct)

Frequencies Dialing

How is the Expected Measured Loss (EML) calculated?

Cable Loss + Central Office Loss + Junction Loss (D) Signup and view all the answers

Which cable type has the lowest loss per kilometer?

Cable # 22 (D) Signup and view all the answers

What is the purpose of loading coils in telephone lines?

To reduce voice frequency attenuation (B) Signup and view all the answers

What frequency corresponds to the digit '5' in Touch Tone Dialing?

770 Hz and 1336 Hz (C) Signup and view all the answers

What is the interdigit delay in pulse dialing?

300 ms (C) Signup and view all the answers

What is the main function of the mouthpiece in a telephone set?

Converts acoustical energy into varying electrical energy (D) Signup and view all the answers

Which component alerts the subscriber of an incoming call?

Telephone ringer (D) Signup and view all the answers

What does the switchhook in a telephone set control?

The flow of current for signaling (A) Signup and view all the answers

What is the purpose of the BORSCHT circuit in telephone systems?

To protect circuits against voltage overload (A) Signup and view all the answers

What is the role of a telephone hybrid?

To convert between four-wire switching and two-wire cables (B) Signup and view all the answers

What kind of signal does the dial in a telephone set generate?

Pulses or tones for establishing connections (C) Signup and view all the answers

What does the earpiece in a telephone do?

Converts varying electrical current back to audible sound (D) Signup and view all the answers

What kind of current does the two-wire system conduct for off-hook signaling?

Direct current (A) Signup and view all the answers

What is the purpose of adding loading coils to a wire?

To increase the distance a local loop can extend (A) Signup and view all the answers

How many loading coils are needed for a subscriber located 10 km from the central office using a 26H88 cable?

2 (A) Signup and view all the answers

What is the most common inductance value for loading coils?

88 mH (B) Signup and view all the answers

Which of the following specifications indicates that a loading coil is commonly used for shorter separations?

26H88 (A) Signup and view all the answers

Which type of coil has the greatest separation distance?

Type D (B) Signup and view all the answers

What is the formula used to determine the number of loading coils needed?

N = 1 + D - 5000/S (C) Signup and view all the answers

What are bridge taps used for in a local loop?

To assign multiple subscribers to a single loop (C) Signup and view all the answers

How does wire gauge affect loop resistance?

Higher gauge offers less resistance and lower attenuation (D) Signup and view all the answers

What is the formula to calculate the dc loop resistance?

$R_{dc} = \frac{90 d^2}{1000}$ (C) Signup and view all the answers

What is the maximum recommended span from the telephone pole to the building?

30m (D) Signup and view all the answers

What is the minimum clearance over areas accessible to pedestrians?

3.5m (D) Signup and view all the answers

What is the recommended material for underground conduit?

Corrosion-resistant material or PVC (B) Signup and view all the answers

What is the minimum depth for conduits under areas used for vehicular traffic?

600mm (D) Signup and view all the answers

What separation distance is required between conduits in well-tamped earth?

300mm (B) Signup and view all the answers

What is the recommended diameter of the service entrance conduit?

50mm (B) Signup and view all the answers

Who were instrumental in the first successful transmission of words over the telephone?

Alexander Graham Bell and Thomas Watson (D) Signup and view all the answers

What was the patent number issued to Alexander Graham Bell for his invention of the telephone?

174,465 (A) Signup and view all the answers

What type of telephone set was introduced in 1951 by the Western Electric Company?

Rotary Dial Telephone (D) Signup and view all the answers

What was a significant barrier that prevented Meucci from obtaining a definitive patent for his invention?

Inability to afford patent fees (A) Signup and view all the answers

Which component serves as the demarcation point between the telephone company and subscriber responsibilities?

Subscriber or Standard Network Interface (SNI) (D) Signup and view all the answers

Which of the following describes the main function of the Manhole in the telephone network?

To facilitate the splicing of cables (B) Signup and view all the answers

What type of cable is the largest used in the local loop, typically containing 3600 pairs of copper wire?

Feeder cable (C) Signup and view all the answers

Which component transmits the signal in a telephone set's wiring?

Tip wire (B) Signup and view all the answers

What was the approximate number of telephones in the world by 1877?

6 (D) Signup and view all the answers

What voltage is typically supplied by the central office to power a telephone set?

-42 to -52 Vdc (A) Signup and view all the answers

Study Notes

Application of Transmission Media

Transmission media are used for the application of telephony.
Telephony systems use various types of transmission media.

Telephony

Telephony involves transmitting sounds and voices over distances.
Early telephony systems used various devices and technologies.
Historical telephone models are shown in images.

Origin of Telephony

Telephony originates from Greek words: "tele" (from afar) and "phone" (sound, voice).
Alexander Graham Bell, assisted by Thomas Watson, transmitted words over the telephone on March 10, 1876.
Bell received patent number 174,465 for his invention.
The contributions of Antonio Meucci were recognized in a US House Resolution of June 11, 2002, but did not affect Bell's patent.

The Truth Behind Bell's Invention

Meucci could not afford the necessary $250 patent fee and filed only a one-year renewable notice in 1871
He failed to get a meeting with Western Union executives, when he attempted to deliver his model and technical details.
Western Union claimed that Meucci's materials were lost in 1874.
Bell, who shared a laboratory with Meucci, then filed for a telephone patent.

Brief History of Telephony

In 1877, there were only six telephones globally.
The first telephone in a single handheld form combining transmitter and receiver was developed in 1878 (Butterstamp Telephone)
In 1881, there were 3,000 telephones.
Bell and Watson sold the rights for telephony systems to AT&T in 1881.
Over 133,000 telephones were in use in the US alone by 1883.
In 1951, Western Electric introduced the Rotary Dial Telephone System 500 type and the DTMF 2500 type telephone systems.

AT&T - American Telephone & Telegraph Company

Also known as Bell Telephone System & Ma Bell
Introduced rotary telephones (500 series)
Developed DTMF telephones (2500 series).
Introduced different telephone types, in various colors, in the 1940s and 1950s.

Parts of the Local Loop

Components consist of the inside plant and the outside plant.
These components include termination boxes, connectors.
Examples of components include feeder cables, distribution cables, subscriber or standard network interfaces (SNI), and drop wires
The main distribution frame (MDF) is a terminal point for both the outside plant and inside plant.
A manhole is underground and often used for splicing cables.
Cross-connect cabinets (SAI) distribute cables.
Poles and fixtures support aerial cables.

Parts of Telephone Set

Mouthpiece: Converts sound waves into electrical signals.
Earpiece: Converts electrical signals back into sound waves.
Dial: Used to generate pulses or tones to connect with specific numbers.
Telephone Ringer: Converts electrical signals into audible ringing sounds.
Switchhook (Cradle): A mechanism that connects and disconnects the telephone from the central office.

Transmission Regulation Circuits

These circuits use capacitors, varistors, and resistors to maintain a stable signal strength.
Sidetone refers to the sound heard by the caller through their own receiver, which is used to help gauge volume.
Telephone Hybrid is a four-wire device where two wires transmit and the other two connect to receivers for a clearer signal.
It allows for direct current for signaling, alternating current for ringing & dial tones, pulse data signals, and supervision signals.

BORSCHT

The BORSCHT circuit handles various voltages to protect the lines from surges and damage.
It enables the circuit to properly route and receive incoming calls and messages.
The Battery also functions for transmitting and receiving DTMF signals.

Kinds of Dialing

Pulse dialing involves a sequence of on-hook and off-hook actions to transmit digits.
Touch-tone dialing utilizes two frequencies (DTMF).

Conditions of Switchhook

On-hook condition describes a telephone set not in use, where the cradle is open.
In this condition, there's no DC current but only AC to ring the bell and announce the call.

Off-Hook Condition

Off-hook condition designates a telephone set in active use, disconnected from the cradle.
It requires a specified minimum current (23mA).

Other Parameters of Local Loop

Expected Measured Loss (EML): combines cable loss, central office loss, and junction loss (measured in decibels).

Loading Coils/H88 Loading

Used to reduce attenuation at voice frequencies.
Loading coils counteract capacitance with inductance for longer cable runs.

Bridge Taps

Allows connection of multiple subscribers on the same local loop, improving flexibility.

Loop Resistance

Wire gauge affects DC resistance.
Lower gauge wires (larger diameter) have lower resistance, better signal.

Building Telephone Facilities

Service Entrance: Wires entering the building, connected to the main cross-connecting point.
General Recommendations for Aerial and Underground Entrances include specifications for conduit sizes and separations to avoid problems and obstructions.
Cable and Wire Color Codes are used to identify different types of cables and their uses within a system.

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Description

Test your knowledge on various aspects of telephone systems, including dialing methods, signal types, and components. This quiz covers topics from pulse dialing to the function of loading coils and BORSCHT circuits. Perfect for students in telecommunications or those interested in the technology behind telephony.