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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.

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  1. What is the significance of the 'eye pattern' in evaluating digital signal quality?

    Answer: It reveals intersymbol interference, noise, and timing jitter in a digital data stream

    An eye pattern (eye diagram) is formed by overlaying successive bit intervals on an oscilloscope; a wide-open eye indicates low ISI and noise, while a closed eye indicates problems.

  2. What is the deviation ratio of an FM signal?

    Answer: The ratio of the maximum frequency deviation to the highest modulating frequency

    Deviation ratio equals peak frequency deviation divided by the highest audio frequency, and it determines the modulation index under worst-case conditions.

  3. In 8-PSK modulation, how many bits are encoded per symbol?

    Answer: 3 bits

    8-PSK has 8 phase states (2³ = 8), so each symbol carries 3 bits of information.

  4. What effect does increasing the modulation index have on an FM signal's bandwidth?

    Answer: Bandwidth increases because additional significant sideband pairs are generated

    Higher modulation index produces more significant Bessel function sideband pairs, which increase the occupied bandwidth of the FM signal.

  5. What is the purpose of forward error correction (FEC) in digital communications?

    Answer: To add redundant bits that allow the receiver to detect and correct errors without retransmission

    FEC encodes data with redundancy so the receiver can identify and correct errors autonomously, making it ideal for one-way or high-latency links.

  6. Which of the following best describes the term 'constellation diagram'?

    Answer: A graphical representation of all possible symbol states in amplitude and phase space

    A constellation diagram plots each possible symbol as a point in a 2D plane defined by in-phase (I) and quadrature (Q) amplitude components.

  7. What is the advantage of using a higher-order modulation scheme such as 64-QAM compared to BPSK on a given channel bandwidth?

    Answer: 64-QAM achieves greater spectral efficiency by encoding more bits per symbol

    64-QAM encodes 6 bits per symbol versus 1 bit for BPSK, transmitting six times more data in the same bandwidth, though it requires a higher SNR.