Extra-Study/pages/E8C.md

E8C Digital signals: digital communication modes; information rate vs. bandwidth; error correction; constellation diagrams

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