Telecom test 1
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What is amplitude?
height of the wave above or below a given reference point (Measured being high or low)
what is frequency?
the number of times a signal makes a complete cycle within a given time frame (Measured in Hertz ((Hz)). Hertz is cycles per second
What is phase?
The position of the waveform relative to a given moment of time (change is in degrees, 0 to 360)
What is bandwidth?
the absolute value of the difference between the lowest and highest frequencies of a signal
What is modulation?
the process of converting digital data into an analog signal
What is pulse code modulation?
an encoding technique that converts analog data to a digital signal. Also known as digitization
What is delta modulation?
A method of converting analog data to digital signal in which the incoming analog signal is tracked and binary 1 or 0, is transmitted, respectively, when the analog signal rises or falls
What is CODEC?
a device that accepts analog data and converts it into digital signals. This process is known as digitization.
What is attenuation?
the continuous loss of strength (power) that a signal experiences as it travels through a medium
What is a modem used for?
a device that modulates digital data on to an analog signal for transmission over a telephone line, then demodulates the analog signal back to digital data
What is a data code?
the set of all textual characters or symbols and their corresponding binary patterns
an 8-bit code allowing 256 possible combinations of texutal symbols (2^8=256)
a 7-bit code that is used to represent all the printable characters on a keyboard plus many nonprintable control characters (2^7=128)
a character encoding technique that can represent all the languages on the planet
Amplification leads to a signal gaining what?
strength (power) of an analog signal
Amplitude Shift Keying
- One amplitude encodes a 0 while another amplitude encodes a 1 (a form of amplitude
Frequency Shift Keying
- One frequency encodes a 0 while another frequency encodes a 1 (a form of frequency
Frequency Shift Keying is subject to what?
intermodulation distortion (frequencies mixing together to create new frequencies)
Phase Shift Keying
- One phase change encodes a 0 while another phase change encodes a 1 (a form of
- phase modulation)
What is the simplest modulation technique?
amplitude shift keying
Most common example of an analog signal
human voice, transmission of a voice conversation
What waveform is continuous?
Which waveform is noncontinuous
Which signal is in a fixed number of forms?
Which signal is harder to separate noise?
Transmitting Analog Data with Analog Signals
transmit analog data, you can modulate the data onto a set of analog signals (broadcast radio and tv)
Transmitting Digital Data and Digital Signals
There are numerous techniques available to convert digital data into digital signals.
Transmitting Digital Data with Discrete Analog Signals
Amplitude shift keying
Frequency shift keying
- Phase shift keying
- Combine two or more to make complex modulation
Transmitting Analog Data with Digital Signals
Pulse code modulation (the more common)
an unwanted coupling between two different signal paths
transmitter and receiver are in visual sight of each other (wireless)
a set of unused frequences between two channels on a frequency division multiplexed system
the noise that occurs when the frequencies of two or more signals mix together and create new frequencies
media selection criteria
a checklist used when designing or updating a computer network that includes cost, speed, distance, right-of-way, expandability,environment, and security
Land-based, line-of-sight transmission
Approximately 20-30 miles between towers
- data at hundreds of millions of bits per second
Signals will not pass through solid objects
Popular with telephone companies and business to business transmissions
- Similar to terrestrial microwave except the signal travels from a ground station on
- earth to a satellite and back to another ground station
Can also transmit signals from one satellite to another
- Satellites can be classified by how far out into orbit each one is (LEO, MEO, GEO, and
- 100 to 1000 miles out
- for wireless e-mail, special mobile telephones, pagers, spying,
1000 to 22,300 miles
Used for GPS (global positioning systems) and government
- over the same position on earth (and always over the equator)
- for weather, television, government operations
HEO (Highly Elliptical Earth orbit)
- follows an elliptical orbit
- Used by the military for spying and by
- scientific organizations for photographing celestial bodies
Which type of twisted pair is used to deal with interference?
shielded twisted pair
Advantage of fiber optic over twisted pair and coaxial cable
safer, less noise, faster
Uses of coaxial cable
carry analog signals wide range of frequencies; good for tv with lots of channels
Examples of conducted media
telephone lines and fiber-optic cables
Which is the simplest and most common type?
twisted pair wire
Twisted Pair Wire
- One or more pairs of single conductor wires that have been twisted around each
- the wires helps to eliminate electromagnetic interference between the two wires
- A single wire wrapped in a foam insulation surrounded by a braided metal shield,
- then covered in a plastic jacket. Cable comes in various thicknesses
- digital signaling in which the cable carries only one channel of digital data]
- uses repeaters
- analog signals and is capable of supporting multiple channels
- A thin glass cable approximately a little thicker than a human hair surrounded by
- a plastic coating and packaged into an insulated cable
- A photo diode or laser generates pulses of light which travel down the fiber
- optic cable and are received by a photo receptor
Thin Fiber Optic Cable
- very little reflection, fast
- transmission, typically uses a laser, longer transmission distances; known as
- single mode fiber
Thick Fiber Optic Cable
- causes more ray collisions, so you have
- to transmit slower
- is step index multimode fiber
- use LED for light source, shorter distance transmissions
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