Ch 1 - P1 Telephony Flashcards
Name the 3 basic components of a telecommunications transmission system.
- Source of energy
- Medium to carry the energy
- Receiving Device
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What is the purpose of an analog telephone?
To convert sound waves into electrical analog signals that can be transmitted over much longer distances than sound waves can travel.
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Early telephones were designed to match the frequencies used in human speech, which included frequencies from 50 Hz to 12 kHz.
False, Although speech may contain frequencies from 50 Hz to 12 kHz, early studies found that good quality speech intelligibility could be obtained if only the frequency range of about 300 Hz to 3400 Hz was actually transmitted. Consequently, this is the frequency band that early telephone circuits were designed to support.
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What is the most significant property of a digital signal?
The most significant property of a digital signal is that at any time it can take on only a value from a discrete set of values.
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What 3 steps are sued to convert an analog signal to a digital signal?
- Filtering
- Sampling.
- Quantizing/companding
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What type of device converts electrical energy back into sound energy?
Receiver
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What does the maximum transmission of electrical power occur in a telephone line?
When a transmitting device and a receiving device have the same load resistance or the same impedance.
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How does impedance differ from resistance?
Both are measured in ohms, but impedance has both a magnitude and a phase component.
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What is the preferred impedance for private line circuits and trunks?
600 ohms
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What is the preferred impedance for CO switching system line circuits?
900 ohms
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When is an echo perceptible during a long distance phone call?
When part of the transmitted signal is sent or reflected back to the originating end.
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What causes part of a signal to be sent back or reflected to the originating end?
Impedance mismatch between the transmission line and the receiver.
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What principal elements contribute to loss and phase distortion at voice frequencies?
- Conductor resistance
- Mutual capacitance of the cable pair
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How does increasing the frequency affect the speed of transmission through cable pairs?
Increasing the frequency increases the speed of transmission.
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Increasing the frequency to increase the speed of transmission does not noticeably affect speech intelligibility.
True. Increasing the frequency to increase the speed of transmission does not noticeably, affect speech intelligibility, but it can have a great affect on data transmission.
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What is the purpose of placing load coils along a cable?
To improve speech transmission quality
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How do load coils improve the quality of speech transmission?
By compensating for the capacitance of a cable pair
By reducing the capacitive current loading in the range of audio frequencies
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What is the most common distance between loading points for D loading?
= 1.37 km (4495 ft)
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What is the most common distance between loading points for H loading?
= 1.83 km (6004 ft)
What types of signals are blocked by loading coils?
Analog high fidelity and digital signals
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How do loading coils affect data transmission?
Load coils adversely affect data transmission.
What determines the upper cutoff frequency of a loading coil?
Loading coil spacing determines the upper cutoff frequency.
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Name 3 common interface options for IP telphony.
- IP telephone
- Computer with IP telephony software and microphone/ speaker or USB handset
- Multifunctional devices with a wireless receiver
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IP telephony software is only operational when the computer is running.
True. IP telephony software is only operational when the computer is running.
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