CRAC Class A (2025) — Questions 371–380
U0370. Amateur stations generally do not use FM phone for Morse code contacts. This is because:
业余电台一般不用调频话方式进行莫尔斯电码通联。这是因 为：
Exam tips · 考试提示
The real reason is regulatory/bandwidth: FM's wide channel far exceeds the narrow necessary bandwidth for Morse (CW), violating the allocation rule to minimize bandwidth. FM technically can carry Morse (B is false), and C/D are not the official rationale.
U0371. Whether FM or SSB modulation, applying an audio signal 10 times the specified input voltage to the microphone input of the transmitter, the most likely result is:
无论是FM还是SSB调制，向发射机的话筒输入端施加10倍于规 定输入电压的音频信号，最可能的结果是：
Exam tips · 考试提示
Overdriving the mic input causes clipping/overmodulation, producing harmonics and intermodulation (IMD) that widen the emission (splatter) and reduce quality. It does not increase range (B/C false) and won't normally burn the PA (D false). 数字通信方式 Digital Communication Modes
U0372. Yaesu System Fusion, abbreviated YSF, is a communication mode integrating digital voice and data transmission. Its characteristics are: (Choose all that apply.)
Yaesu System Fusion简称YSF，是数字语音和数据传输相互 融合的一种通信方式，特点是：
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YSF (Yaesu System Fusion) is a widely used amateur digital voice+data mode, works through repeaters, and uses C4FM modulation (A, B, C). D is false: YSF is C4FM/FDMA based, not TDMA (TDMA is used by some other systems such as DMR).
U0373. The Icom D-STAR System provides a data communication mode, whose characteristics are: (Choose all that apply.)
Icom D-STAR System提供了一种数据通信方式，特点是：
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D-STAR is a widely used amateur digital voice/data system: it works via repeaters (B), supports Internet linking and personal hotspots (C), and carries GPS position reports (D). All four statements are correct.
U0374. FreeDV is a digital voice mode. Its characteristics are: (Choose all that apply.)
FreeDV是一种数字语音方式。其特点是：
Exam tips · 考试提示
FreeDV is an open-source, narrowband HF digital voice mode that lets hams experiment with DSP and build their own gear (A, B, C). D is false: FreeDV is designed for SSB transceivers, not FM handhelds, and "especially beautiful audio" is not a characteristic.
U0375. Digital amateur television (DATV) is a mode applying digital audio/video compression coding to real-time image communication. When conducting DATV contacts via a satellite transponder, amateurs generally choose the DVB-S2 protocol; the modulation may be: (Choose all that apply.)
数字业余电视（DATV）是将数字音视频压缩编码实验用于实 时图像通信的一种方式。通过卫星转发器进行DATV联络时， 爱好者们普遍选用DVB-S2协议，调制方式可以是：
Exam tips · 考试提示
DVB-S2 (used for satellite DATV) supports several modulation schemes: QPSK, 8PSK, 16APSK and 32APSK. All four are valid DVB-S2 modulations, so all are correct.
U0376. When using the DRM protocol for digital slow-scan television (DSSTV) communication, amateurs always tend to transmit the DSSTV baseband (generated within the audio range) via single sideband rather than FM phone. The main reason is:
使用DRM协议进行数字慢扫描电视（DSSTV）通信时，爱好 者总是倾向于通过单边带而非调频话方式来传输在音频范围内 生成的DSSTV基带。主要原因是：
Exam tips · 考试提示
SSB linearly passes the audio-range DSSTV baseband without FM's threshold/nonlinearity, preserving the digital signal and aiding error control in fading. B conflates cause (FM's threshold does widen bandwidth but the stated main reason is A's baseband fidelity); C/D mischaracterize FM's effect on quality. 无线电系统基本原理 3 C H A P T E R Basic Principles of Radio Systems 本章从收发信机、天线、传输线到调制与卫星，建立无线电系统的整体认知。This chapter builds a systems-level understanding from transceivers, antennas and feed lines to modulation and amateur satellites. 收发信机与接收系统 Transceivers and Receiver Systems
U0377. What is a transceiver (收发信机)?
什么是收发信机？
Exam tips · 考试提示
收发信机 (transceiver) = a combined receiver + transmitter in one unit. B is a repeater, C is a digital relay/node, D is a voice converter — none is a transceiver.
U0378. What components does a working radio receiving system minimally contain? (Choose all that apply.)
一个可以工作的无线电接收系统至少包含哪些部件？
Exam tips · 考试提示
A minimal receiving system needs an antenna (to capture the signal) and a demodulator/detector (to recover the information). A potentiometer (C) and a power supply (D) are not strictly required for the basic receive chain concept (e.g., a crystal earpiece set).
U0379. What components does a working radio transmitting system minimally contain? (Choose all that apply.)
一个可以工作的无线电发射系统至少包含哪些部件？
Exam tips · 考试提示
A minimal transmit system needs an RF oscillator (to generate the carrier), a modulator (to impress information), and a transmit antenna (to radiate). A lightning arrester (D) is a safety add-on, not part of the basic chain.