Modulation and Digital Signals Flashcards
7 cards from real HAM practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Modulation and Digital Signals flashcards as text
What is the purpose of pre-emphasis in an FM transmitter?
Answer: To increase the deviation of higher audio frequencies before transmission
Pre-emphasis boosts higher audio frequencies before transmission to improve the signal-to-noise ratio, and de-emphasis at the receiver restores flat frequency response.
Which modulation method conveys information by varying the timing of pulses relative to a reference clock?
Answer: Pulse position modulation (PPM)
Pulse position modulation (PPM) encodes information in the time displacement of each pulse from a fixed reference position.
In a phase-locked loop (PLL) frequency synthesizer, what does the voltage-controlled oscillator (VCO) output frequency depend on?
Answer: The DC control voltage from the loop filter
The VCO output frequency is controlled by a DC voltage produced by the loop filter, which integrates the phase detector error signal.
What is the principal advantage of using OFDM (Orthogonal Frequency-Division Multiplexing) in digital HF communications?
Answer: It is highly resistant to multipath fading and selective fading
OFDM spreads data across many narrow subcarriers that are orthogonal to each other, making the signal robust against multipath and frequency-selective fading common on HF.
What does the term 'frequency deviation' refer to in FM modulation?
Answer: The peak change in instantaneous carrier frequency from the unmodulated carrier frequency
Frequency deviation is the maximum instantaneous shift of the carrier frequency above or below the rest frequency, determined by the amplitude of the modulating signal.
In single sideband (SSB) transmission, why is the carrier suppressed?
Answer: To conserve power since the carrier carries no information
The carrier in AM contains no information, so suppressing it allows all transmitter power to be concentrated in the information-bearing sideband.
What is the function of a balanced modulator in a SSB transmitter?
Answer: To produce a double-sideband suppressed-carrier (DSBSC) signal
A balanced modulator combines the carrier and audio in a way that cancels the carrier, producing a double-sideband suppressed-carrier signal that a sideband filter then reduces to one sideband.