93 lines
4.1 KiB
Markdown
93 lines
4.1 KiB
Markdown
E8C Digital signals: digital communication modes; information rate vs. bandwidth; error correction; constellation diagrams
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- [[E8C01]] (B)
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What is Quadrature Amplitude Modulation or QAM? #card
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- [[A.]] A technique for digital data compression used in digital television which removes redundancy in the data by comparing bit amplitudes
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- [[B.]] Transmission of data by modulating the amplitude of two carriers of the same frequency but 90 degrees out of phase
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- [[C.]] A method of performing single sideband modulation by shifting the phase of the carrier and modulation components of the signal
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- [[D.]] A technique for analog modulation of television video signals using phase modulation and compression
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- [[E8C02]] (C)
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What is the definition of symbol rate in a digital transmission? #card
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- [[A.]] The number of control characters in a message packet
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- [[B.]] The maximum rate at which the forward error correction code can make corrections
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- [[C.]] The rate at which the waveform changes to convey information
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- [[D.]] The number of characters carried per second by the station-to-station link
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- [[E8C03]] (A)
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Why should the phase of a PSK signal be changed at the zero crossing of the RF signal? #card
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- [[A.]] To minimize bandwidth
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- [[B.]] To simplify modulation
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- [[C.]] To improve carrier suppression
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- [[D.]] All these choices are correct
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- [[E8C04]] (C)
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What technique minimizes the bandwidth of a PSK31 signal? #card
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- [[A.]] Zero-sum character encoding
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- [[B.]] Reed-Solomon character encoding
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- [[C.]] Use of sinusoidal data pulses
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- [[D.]] Use of linear data pulses
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- [[E8C05]] (C)
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What is the approximate bandwidth of a 13-WPM International Morse Code transmission? #card
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- [[A.]] 13 Hz
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- [[B.]] 26 Hz
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- [[C.]] 52 Hz
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- [[D.]] 104 Hz
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- [[E8C06]] (B)
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What is the bandwidth of an FT8 signal? #card
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- [[A.]] 10 Hz
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- [[B.]] 50 Hz
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- [[C.]] 600 Hz
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- [[D.]] 2.4 kHz
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- [[E8C07]] (A)
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What is the bandwidth of a 4,800-Hz frequency shift, 9,600-baud ASCII FM transmission? #card
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- [[A.]] 15.36 kHz
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- [[B.]] 9.6 kHz
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- [[C.]] 4.8 kHz
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- [[D.]] 5.76 kHz
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- [[E8C08]] (D)
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How does ARQ accomplish error correction? #card
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- [[A.]] Special binary codes provide automatic correction
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- [[B.]] Special polynomial codes provide automatic correction
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- [[C.]] If errors are detected, redundant data is substituted
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- [[D.]] If errors are detected, a retransmission is requested
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- [[E8C09]] (D)
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Which digital code allows only one bit to change between sequential code values? #card
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- [[A.]] Binary Coded Decimal Code
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- [[B.]] Extended Binary Coded Decimal Interchange Code
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- [[C.]] Extended ASCII
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- [[D.]] Gray code
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- [[E8C10]] (C)
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How can data rate be increased without increasing bandwidth? #card
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- [[A.]] It is impossible
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- [[B.]] Increasing analog-to-digital conversion resolution
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- [[C.]] Using a more efficient digital code
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- [[D.]] Using forward error correction
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- [[E8C11]] (A)
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What is the relationship between symbol rate and baud? #card
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- [[A.]] They are the same
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- [[B.]] Baud is twice the symbol rate
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- [[C.]] Baud rate is half the symbol rate
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- [[D.]] The relationship depends on the specific code used
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- [[E8C12]] (C)
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What factors affect the bandwidth of a transmitted CW signal? #card
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- [[A.]] IF bandwidth and Q
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- [[B.]] Modulation index and output power
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- [[C.]] Keying speed and shape factor (rise and fall time)
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- [[D.]] All these choices are correct
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- [[E8C13]] (B)
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What is described by the constellation diagram of a QAM or QPSK signal? #card
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- [[A.]] How many carriers may be present at the same time
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- [[B.]] The possible phase and amplitude states for each symbol
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- [[C.]] Frequency response of the signal stream
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- [[D.]] The number of bits used for error correction in the protocol
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- [[E8C14]] (C)
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What type of addresses do nodes have in a mesh network? #card
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- [[A.]] Email
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- [[B.]] Trust server
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- [[C.]] Internet Protocol (IP)
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- [[D.]] Talk group
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- [[E8C15]] (C)
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What technique do individual nodes use to form a mesh network? #card
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- [[A.]] Forward error correction and Viterbi codes
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- [[B.]] Acting as store-and-forward digipeaters
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- [[C.]] Discovery and link establishment protocols
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- [[D.]] Custom code plugs for the local trunking systems
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