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What is amplitude?
height of the wave above or below a given reference point (Measured being high or low)
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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
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What is phase?
The position of the waveform relative to a given moment of time (change is in degrees, 0 to 360)
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What is bandwidth?
the absolute value of the difference between the lowest and highest frequencies of a signal
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What is modulation?
the process of converting digital data into an analog signal
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What is pulse code modulation?
an encoding technique that converts analog data to a digital signal. Also known as digitization
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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
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What is CODEC?
a device that accepts analog data and converts it into digital signals. This process is known as digitization.
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What is attenuation?
the continuous loss of strength (power) that a signal experiences as it travels through a medium
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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
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What is a data code?
the set of all textual characters or symbols and their corresponding binary patterns
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EBCDIC
an 8-bit code allowing 256 possible combinations of texutal symbols (2^8=256)
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ASCII
a 7-bit code that is used to represent all the printable characters on a keyboard plus many nonprintable control characters (2^7=128)
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Unicode
a character encoding technique that can represent all the languages on the planet
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Amplification leads to a signal gaining what?
strength (power) of an analog signal
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Amplitude Shift Keying
- One amplitude encodes a 0 while another amplitude encodes a 1 (a form of amplitude
- modulation)
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Frequency Shift Keying
- One frequency encodes a 0 while another frequency encodes a 1 (a form of frequency
- modulation)
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Frequency Shift Keying is subject to what?
intermodulation distortion (frequencies mixing together to create new frequencies)
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Phase Shift Keying
- One phase change encodes a 0 while another phase change encodes a 1 (a form of
- phase modulation)
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What is the simplest modulation technique?
amplitude shift keying
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Most common example of an analog signal
human voice, transmission of a voice conversation
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What waveform is continuous?
analog
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Which waveform is noncontinuous
digital
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Which signal is in a fixed number of forms?
digital
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Which signal is harder to separate noise?
analog
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Transmitting Analog Data with Analog Signals
transmit analog data, you can modulate the data onto a set of analog signals (broadcast radio and tv)
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Transmitting Digital Data and Digital Signals
There are numerous techniques available to convert digital data into digital signals.
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Transmitting Digital Data with Discrete Analog Signals
Amplitude shift keying
Frequency shift keying
- Phase shift keying
- Combine two or more to make complex modulation
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Transmitting Analog Data with Digital Signals
Pulse code modulation (the more common)
Delta modulation
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Crosstalk
an unwanted coupling between two different signal paths
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line-of-sight transmission
transmitter and receiver are in visual sight of each other (wireless)
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guardbands
a set of unused frequences between two channels on a frequency division multiplexed system
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intermodulation distortion
the noise that occurs when the frequencies of two or more signals mix together and create new frequencies
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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
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Terrestrial Microwave
Land-based, line-of-sight transmission
Approximately 20-30 miles between towers
- Transmits
- 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
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Satellite Microwave
- 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
- HEO)
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LEO (Low-Earth-Orbit)
- 100 to 1000 miles out
- Used
- for wireless e-mail, special mobile telephones, pagers, spying,
- videoconferencing
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MEO(Middle-Earth-Orbit)
1000 to 22,300 miles
Used for GPS (global positioning systems) and government
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GEO (Geosynchronous-Earth-Orbit)
- Always
- over the same position on earth (and always over the equator)
- Used
- for weather, television, government operations
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HEO (Highly Elliptical Earth orbit)
- satellite
- follows an elliptical orbit
- Used by the military for spying and by
- scientific organizations for photographing celestial bodies
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Which type of twisted pair is used to deal with interference?
shielded twisted pair
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Advantage of fiber optic over twisted pair and coaxial cable
safer, less noise, faster
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Uses of coaxial cable
carry analog signals wide range of frequencies; good for tv with lots of channels
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Examples of conducted media
telephone lines and fiber-optic cables
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Which is the simplest and most common type?
twisted pair wire
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Twisted Pair Wire
- One or more pairs of single conductor wires that have been twisted around each
- other
- Twisting
- the wires helps to eliminate electromagnetic interference between the two wires
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Coaxial Cable
- 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
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Baseband
coaxial technology
- uses
- digital signaling in which the cable carries only one channel of digital data]
- uses repeaters
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Broadband
coaxial technology
- transmits
- analog signals and is capable of supporting multiple channels
Use amplifiers
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Fiber-Optic Cable
- 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
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Thin Fiber Optic Cable
- very little reflection, fast
- transmission, typically uses a laser, longer transmission distances; known as
- single mode fiber
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Thick Fiber Optic Cable
- causes more ray collisions, so you have
- to transmit slower
- This
- is step index multimode fiber
- Typically
- use LED for light source, shorter distance transmissions
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