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Amateur Extra - Signals, modulation, and digital modes
Signals, modulation, and digital modes groups the E8 section questions for focused review and easier weak-point tracking.
48
Questions
9
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- Amateur Extra
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- Signals, modulation, and digital modes
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Read the condition in the stem before comparing key terms in the options.
Study rules, calculations, and equipment questions as separate patterns.
After this topic, return to the full pool for mixed practice.
Topic Study Guide
This topic covers signal analysis, modulation techniques (FM/PM/SSB), and advanced digital modes (QAM, OFDM, spread spectrum). The focus is on calculating modulation index, estimating bandwidth, and understanding digital signal processing concepts.
High-Yield Checks
- FM Modulation Index & Deviation Ratio: Master the formula (max deviation ÷ highest modulating frequency) and distinguish between FM and PM characteristics.
- Bandwidth Calculations: Memorize the CW bandwidth estimation (WPM × 4) and Carson's Rule for FM signal bandwidth.
- Signal Analysis & ADCs: Understand Fourier analysis (sine waves and odd harmonics), time domain (amplitude vs time), and ADC resolution (8-bit = 256 levels).
- Advanced Digital Modulation: Be familiar with QAM (amplitude of two carriers 90 degrees out of phase), OFDM (subcarriers avoiding intersymbol interference), and Direct Sequence spread spectrum.
Trap Patterns
- Confusing Baud with Bit Rate: Baud is exactly the symbol rate. Do not confuse it with bit rate, which depends on the modulation scheme.
- Misunderstanding PM Modulation Index: The modulation index of Phase Modulation (PM) does not depend on the RF carrier frequency.
- Extremely short rise/fall time on CW: This causes key clicks (splatter), not RF harmonics.
- Confusing Time and Frequency Domains: The time domain describes amplitude at different times, not frequency at different times.
Review Steps
- Memorize formulas: Write down the formulas for FM modulation index, deviation ratio, and CW/FM bandwidth on flashcards for repeated review.
- Clarify digital mode terms: Compare the definitions of QAM, OFDM, FDM, and spread spectrum, focusing on key features (e.g., 90-degree phase difference for QAM).
- Understand signal analysis basics: Review Fourier analysis, time vs. frequency domains, and ADC principles including quality metrics like THD.
- Use diagrams for deeper understanding: Learn how a constellation diagram represents the phase and amplitude states for each symbol.
Quick Checks
- How do you calculate the modulation index of an FM signal?
- What is the approximate bandwidth of a 13-WPM CW signal?
- What is described by the constellation diagram of a QAM or QPSK signal?
- Which spread spectrum technique uses a high-speed binary bit stream to shift the phase of an RF carrier?
Questions in This Topic
Choose Practice ModeE8A01What technique shows that a square wave is made up of a sine wave and its odd harmonics?E8A02Which of the following is a type of analog-to-digital conversion?E8A03Which of the following describes a signal in the time domain?E8A04What is “dither” with respect to analog-to-digital converters?E8A05What is the benefit of making voltage measurements with a true-RMS calculating meter?E8A06What is the approximate ratio of PEP-to-average power in an unprocessed single-sideband phone signal?E8A07What determines the PEP-to-average power ratio of an unprocessed single-sideband phone signal?E8A08Why are direct or flash conversion analog-to-digital converters used for a software defined radio?E8A09How many different input levels can be encoded by an analog-to-digital converter with 8-bit resolution?E8A10What is the purpose of a low-pass filter used at the output of a digital-to-analog converter?E8A11Which of the following is a measure of the quality of an analog-to-digital converter?E8B01What is the modulation index of an FM signal?E8B02How does the modulation index of a phase-modulated emission vary with RF carrier frequency?E8B03What is the modulation index of an FM phone signal having a maximum frequency deviation of 3000 Hz either side of the carrier frequency if the highest modulating frequency is 1000 Hz?E8B04What is the modulation index of an FM phone signal having a maximum carrier deviation of plus or minus 6 kHz if the highest modulating frequency is 2 kHz?E8B05What is the deviation ratio of an FM phone signal having a maximum frequency swing of plus or minus 5 kHz if the highest modulation frequency is 3 kHz?E8B06What is the deviation ratio of an FM phone signal having a maximum frequency swing of plus or minus 7.5 kHz if the highest modulation frequency is 3.5 kHz?E8B07Orthogonal frequency-division multiplexing (OFDM) is a technique used for which types of amateur communication?E8B08What describes orthogonal frequency-division multiplexing (OFDM)?E8B09What is deviation ratio?E8B10What is frequency division multiplexing (FDM)?E8B11What is digital time division multiplexing?E8C01What is Quadrature Amplitude Modulation or QAM?E8C02What is the definition of symbol rate in a digital transmission?E8C03Why should the phase of a PSK signal be changed at the zero crossing of the RF signal?E8C04What technique minimizes the bandwidth of a PSK31 signal?E8C05What is the approximate bandwidth of a 13-WPM International Morse Code transmission?E8C06What is the bandwidth of an FT8 signal?E8C07What is the bandwidth of a 4,800-Hz frequency shift, 9,600-baud ASCII FM transmission?E8C08How does ARQ accomplish error correction?E8C09Which digital code allows only one bit to change between sequential code values?E8C10How can data rate be increased without increasing bandwidth?E8C11What is the relationship between symbol rate and baud?E8C12What factors affect the bandwidth of a transmitted CW signal?E8C13What is described by the constellation diagram of a QAM or QPSK signal?E8C14What type of addresses do nodes have in a mesh network?E8C15What technique do individual nodes use to form a mesh network?E8D01Why are received spread spectrum signals resistant to interference?E8D02What spread spectrum communications technique uses a high-speed binary bit stream to shift the phase of an RF carrier?E8D03Which describes spread spectrum frequency hopping?E8D04What is the primary effect of extremely short rise or fall time on a CW signal?E8D05What is the most common method of reducing key clicks?E8D06What is the advantage of including parity bits in ASCII characters?E8D07What is a common cause of overmodulation of AFSK signals?E8D08What parameter evaluates distortion of an AFSK signal caused by excessive input audio levels?E8D09What is considered an acceptable maximum IMD level for an idling PSK signal?E8D10What are some of the differences between the Baudot digital code and ASCII?E8D11What is one advantage of using ASCII code for data communications?