CRAC Bilingual Manual › Part: Radio System Fundamentals
CRAC Bilingual Exam Manual (Class A / B / C) | 中国业余无线电台操作技术能力验证英中对照手册
This section covers Transceivers and Receiver Systems with 60 bilingual questions from the CRAC 2025 question bank. Each question shows the original Chinese (left) and the English translation (right). The correct answer is highlighted in green, followed by a Knowledge Point Analysis and Candidate Tips covering US–China differences, common pitfalls, and real on-air practice.
Class badges ABC indicate which license-class syllabus includes each question. Class A is the entry level, Class B adds HF privileges, and Class C is the advanced level.
什么是收发信机？
- A一种组合了接收机和发射机的无线电通信设备
- B一种将收到的信号再行转发的设备
- C一种将收到的信息解码，纠错并转发的设备
- D一种将数字话音转换为模拟话音并转发的设备
What is a transceiver (收发信机)?
- Aa radio communication device that combines a receiver and a transmitter
- Ba device that re-transmits a received signal
- Ca device that decodes, error-corrects, and forwards received information
- Da device that converts digital voice to analog voice and forwards it
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.
US–China difference: “Transceiver” is the identical English term in the US.
Common pitfall: Confusing transceiver with repeater (转发).
Real on-air practice: Your handheld is a transceiver.
一个可以工作的无线电接收系统至少包含哪些部件？
- A接收天线
- B解调器
- C电位器
- D电源
What components does a working radio receiving system minimally contain? (Choose all that apply.)
- Areceiving antenna
- Bdemodulator (detector)
- Cpotentiometer
- Dpower supply
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).
US–China difference: Same fundamental Rx chain (antenna → detector) in US beginner theory.
Common pitfall: Including the power supply as essential — the core receive path is antenna + demodulator.
Real on-air practice: A simple fox-hunt receiver is just an antenna, detector, and earphone.
一个可以工作的无线电发射系统至少包含哪些部件？
- A射频振荡器
- B调制器
- C发射天线
- D防雷器
What components does a working radio transmitting system minimally contain? (Choose all that apply.)
- ARF oscillator
- Bmodulator
- Ctransmit antenna
- Dlightning arrester
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.
US–China difference: Same Tx building blocks (oscillator, modulator, antenna) in US theory.
Common pitfall: Adding the arrester as essential — it’s protective, not functional.
Real on-air practice: A basic CW transmitter = oscillator + key (modulator) + antenna.
为什么业余无线电收发信机所用的直流电源线要尽量短，尽量粗？
- A减小发信时电源线上的压降
- B分流机箱外表面的射频电流
- C防止收发信机意外滑落摔坏
- D厂商销售电源线的一种策略
Why should the DC power cable used by an amateur transceiver be as short and as thick as possible?
- Ato reduce the voltage drop on the power cable during transmission
- Bto divert RF current flowing on the exterior of the chassis
- Cto prevent the transceiver from accidentally falling and breaking
- Da sales tactic by the manufacturer
A short, thick DC cable minimizes resistance, reducing the voltage drop when the PA draws high current during transmit, so the rig gets stable voltage. B/C/D are unrelated or absurd.
US–China difference: Same good-practice advice in US manuals (short/heavy DC leads).
Common pitfall: Thinking it’s for RF grounding (B) — it’s about DC voltage drop.
Real on-air practice: A 100 W HF rig on long thin leads may brown out on transmit.
单工操作（simplex operation）是指：在一条电信通路的两个方向上交替进行传输的一种工作方式。下列通信采用单工操作方式：
- A两台由PTT键转换收发状态的业余对讲机之间的通信
- B两台有线电话座机之间的通信
- C两台公众移动电话终端（手机）之间的通信
- D一台业余中继台与一台由PTT键转换收发状态的业余对讲机之间的通信
Simplex operation means a mode of operation in which transmission alternates in the two directions of a telecommunication channel. Which of the following communications uses simplex operation:
- Acommunication between two amateur handhelds whose transmit/receive state is switched by a PTT key
- Bcommunication between two wired telephone handsets
- Ccommunication between two public mobile phones
- Dcommunication between an amateur repeater and an amateur handheld switched by a PTT key
Simplex = both stations transmit and receive on the same frequency, taking turns (PTT switches one at a time). Two PTT handhelds on the same frequency is simplex. A repeater link (D) is semi-duplex; phones (B/C) are full duplex.
US–China difference: Simplex (same frequency, push-to-talk) is the same concept in the US.
Common pitfall: Confusing simplex with a repeater contact (which uses different TX/RX frequencies).
Real on-air practice: Two hams talking on 146.520 MHz simplex (no repeater).
双工操作（duplex operation）是指：一条电信通路的两个方向能同时进行传输的工作方式。下列通信采用双工操作方式：
- A由一台连续工作的430MHz接收机和一台144MHz发信机组成的地面业余电台与业余卫星之间的通信
- B两台具有QSK功能的业余CW收发信之间的通信
- C一台业余中继台与一台由PTT键转换收发状态的业余对讲机之间的通信
- D两台由PTT键转换收发状态的业余对讲机之间的通信
Duplex operation means a mode in which the two directions of a telecommunication channel can transmit simultaneously. Which of the following communications uses duplex operation:
- Acommunication between a terrestrial amateur station consisting of a continuously operating 430 MHz receiver and a 144 MHz transmitter, and an amateur satellite
- Bcommunication between two amateur CW transceivers with QSK (full break-in) capability
- Ccommunication between an amateur repeater and an amateur handheld switched by a PTT key
- Dcommunication between two amateur handhelds switched by a PTT key
True duplex = simultaneous two-way transmission. A ground station using a separate 430 MHz receiver and 144 MHz transmitter to a satellite receives and transmits at the same time → full duplex. B (QSK) is very fast T/R switching (effectively full break-in but still alternating, not simultaneous), while C is semi-duplex and D is simplex.
US–China difference: Satellite ground stations operating separate uplink/downlink frequencies is duplex in the US too.
Common pitfall: Treating QSK (fast break-in) as true duplex — it is rapid alternating, not simultaneous.
Real on-air practice: Working a linear transponder satellite, you hear yourself while transmitting.
半双工操作（semi-duplex operation）是指：电路的一端用单工操作，另一端用双工操作的一种工作方式。下列通信采用半双工操作方式：
- A一台业余中继台与一台由PTT键转换收发状态的业余对讲机之间的通信
- B两台具有QSK功能的业余CW收发信之间的通信
- C两台由PTT键转换收发状态的业余对讲机之间的通信
- D两台公众移动电话终端（手机）之间的通信
Semi-duplex operation means a mode where one end of the circuit uses simplex and the other end uses duplex. Which of the following communications uses semi-duplex operation:
- Acommunication between an amateur repeater and an amateur handheld switched by a PTT key
- Bcommunication between two amateur CW transceivers with QSK capability
- Ccommunication between two amateur handhelds switched by a PTT key
- Dcommunication between two public mobile phones
Semi-duplex = one end full duplex (the repeater receives and transmits at once on different frequencies) and the other end simplex (the handheld, PTT-switched). That is exactly A. B is QSK, C is simplex, D is full duplex.
US–China difference: A repeater-to-handheld contact is semi-duplex in the US too.
Common pitfall: Calling a repeater contact “duplex” — only the repeater end is duplex.
Real on-air practice: You use a repeater (your radio simplex, the machine full duplex).
收发信机中的PTT是指什么信号？
- A按键发射，有信号（一般为对地接通）时发射机由等待转为发射
- B发信语音压缩，对音频输入电平进行检测并反馈控制，以提升语音包络幅度较小的部分
- C收信机前置放大器，在接收微弱信号时接入（此时某些技术指标可能低于额定值）
- D自动天线调谐，对天线电路的电压驻波比进行检测并进行自动补偿，以维持最小驻波比
What signal does PTT in a transceiver refer to?
- Apush-to-talk: when the signal is present (typically grounded), the transmitter switches from standby to transmit
- Btransmit speech compression that detects the audio input level and applies feedback control to boost the lower-amplitude parts of the speech envelope
- Ca receiver preamplifier that is switched in when receiving weak signals (where some specs may fall below rated values)
- Dautomatic antenna tuning that detects the VSWR of the antenna circuit and automatically compensates to maintain minimum SWR
PTT = Push-To-Talk: pressing the key grounds a line that switches the rig from receive/standby to transmit. B is speech processing, C is a preamp, D is automatic antenna tuning (ATU) — none is PTT.
US–China difference: PTT is the universal term and function in US transceivers.
Common pitfall: Confusing PTT with the mic’s speech compressor or the ATU.
Real on-air practice: Hold the PTT to talk, release to listen.
收发信机面板上或设置菜单中的符号SQL代表什么功能？
- A静噪控制，用来调整静噪阈值的大小
- B发信语音压缩，对音频输入电平进行检测并反馈控制，以提升语音包络幅度较小的部分
- C收信机前置放大器，在接收微弱信号时接入（此时某些技术指标可能低于额定值）
- D自动天线调谐，对天线电路的电压驻波比进行检测并进行自动补偿，以维持最小驻波比
What function does the symbol SQL on the transceiver panel or in the setup menu represent?
- Asquelch control, used to adjust the squelch threshold level
- Btransmit speech compression, which detects the audio input level and provides feedback control to raise the portions of the speech envelope with smaller amplitude
- Creceiver preamplifier, engaged when receiving weak signals (some specifications may be below rated values at this time)
- Dautomatic antenna tuning, which detects the voltage standing-wave ratio (SWR) of the antenna circuit and automatically compensates to maintain the minimum SWR
SQL is the universal front-panel/Menu abbreviation for Squelch (静噪). Squelch mutes the receiver’s audio output when the received signal-to-noise ratio falls below a set threshold, so the operator is not subjected to constant background hiss. Option A states exactly this. The other choices describe unrelated functions: B is speech compression (PROC), C is the preamplifier (PRE), and D is automatic antenna tuning (AT/TUNE).
US–China difference: Identical concept; “SQL” / squelch is labeled the same way on US (FCC Part 97) and Chinese amateur transceivers.
Common pitfall: Confusing SQL (squelch) with NB (noise blanker) — both reduce noise but squelch simply mutes below a threshold while a noise blanker slices off impulse spikes. Do not pick NB when the question asks for SQL.
Real on-air practice: On a busy 2-meter FM repeater you keep squelch just above the noise floor (e.g. threshold 1–2) so the radio stays silent between QSOs and opens only when a station keys up.
收发信机设置静噪功能的目的是什么？
- A在没有信号的情况下关闭音频输出，避免播放刺耳的噪声
- B滤除所收信号中的噪声，使对方的话音变得清晰
- C滤除发信方的环境噪声，使发出的话音更为清晰
- D自动控制收信机的增益，避免信号过强时发生阻塞或失真
What is the purpose of setting the squelch function on a transceiver?
- Ato mute the audio output when there is no signal, avoiding the playback of harsh noise
- Bto filter out the noise in the received signal, making the other party’s voice clearer
- Cto filter out the ambient noise at the transmitting end, making the transmitted voice clearer
- Dto automatically control the receiver gain, avoiding blocking or distortion when the signal is too strong
Squelch (静噪) is a receive-side gate: it suppresses the audio path whenever no usable signal is present, so the operator hears silence instead of receiver hiss. Option A captures this precisely. B and C describe noise filtering/processing of the actual audio, which squelch does not do; D describes automatic gain control (AGC), a different function.
US–China difference: Same function and purpose on US and Chinese radios.
Common pitfall: Thinking squelch “cleans up” a weak voice signal. It does not improve intelligibility — opening the squelch on a weak station actually lets more noise through; you must raise RF gain or use a preamp/NB instead.
Real on-air practice: When hunting for a faint weak-signal station you often open squelch (threshold 0) and listen on headphones; the background noise tells you the band is clear.
需要聆听非常微弱的FM信号时应如何设置收发信机的静噪？
- A关闭静噪或将阈值设为0，使接收机的音频输出不受限制
- B尽可能调高接收机的音量
- C关闭VOX功能
- D调节VOX，使之处于最灵敏的状态
When you need to listen for very weak FM signals, how should you set the transceiver’s squelch?
- Aturn off the squelch or set the threshold to 0, so that the receiver’s audio output is unrestricted
- Bturn up the receiver volume as high as possible
- Cturn off the VOX function
- Dadjust the VOX to its most sensitive state
Because squelch mutes the audio whenever the signal is below its threshold, a very weak station that rides near or below the threshold will be cut off or hard to hear. Disabling squelch (or setting the threshold to 0) removes that gate so the audio path passes even the weakest signal. B only raises loudness, not sensitivity; C and D concern VOX (transmit voice control), which is irrelevant to receiving.
US–China difference: Same technique on US and Chinese FM radios — “carrier squelch off / threshold 0” to copy weak carriers.
Common pitfall: Raising the volume instead of opening squelch — that makes the noise louder but still mutes the weak station once the threshold is exceeded.
Real on-air practice: During a VHF FM “weak-signal” listening session you open squelch and listen on headphones; you hear the continuous hiss plus the buried station rather than silence.
用带有静噪功能的FM收发信机接收FM话音，我们有时会在发射方松开PTT的时候听到一种比较短促的“嘶”或“喀拉”的噪声拖尾。这是因为：
- A此类电路根据接收机鉴频输出的高音频噪声的大小来判断信号消失与否，并据此控制音频输出。这种检测需要一定的时间才能完成，这导致短暂泄漏刺耳的噪声
- B该噪声是发射台话筒的PTT键接点跳动所致，发射到接收端时还可能带有“叮”的声音
- C该噪声是发射台的一种有目的所为，例如是用作结束发射的标志，有时是“嘟”的声音
- D这是由接收机的自动增益电路的时间常数造成
When receiving FM voice with a squelch-equipped FM transceiver, we sometimes hear a brief “hiss” or “crackle” noise tail when the transmitting party releases the PTT. This is because:
- Athis type of circuit determines whether the signal has disappeared based on the level of high-frequency audio noise at the receiver’s discriminator output, and controls the audio output accordingly. This detection takes a certain amount of time to complete, which causes brief leakage of harsh noise
- Bthis noise is caused by the bouncing of the PTT key contact of the transmitting station’s microphone, and may also carry a “ding” sound when transmitted to the receiving end
- Cthis noise is an intentional act of the transmitting station, e.g., used as a sign of ending transmission, sometimes a “beep” sound
- Dthis is caused by the time constant of the receiver’s automatic gain control circuit
The “squelch tail” is a well-known artifact of carrier/noise-operated squelch on FM. The circuit senses the disappearance of the signal by monitoring the high-frequency (quieting) noise at the discriminator output; the sense-and-switch action has a finite time constant, so for a few tens of milliseconds after the carrier drops the audio path is still open and the harsh receiver hiss leaks through. A describes this correctly. B/C attribute it to the transmitter (it is a receiver-side effect), and D confuses it with AGC.
US–China difference: Same phenomenon and explanation on US FM radios; it is inherent to carrier-squelch design everywhere.
Common pitfall: Assuming the tail is a fault in the other station’s microphone or a deliberate sign-off tone. It is simply the local receiver’s squelch release delay.
Real on-air practice: Many repeaters add a brief “squelch tail” (often with a courtesy beep or a tail delay) so the user’s radio does not cut off the end of the other station’s speech — the same physics, used deliberately.
收发信机面板上或设置菜单中的符号VOL代表什么功能？
- A音量控制，用来调整接收机放出的声音大小
- B发信语音压缩，对音频输入电平进行检测并反馈控制，以提升语音包络幅度较小的部分
- C收信机前置放大器，在接收微弱信号时接入（此时某些技术指标可能低于额定值）
- D自动天线调谐，对天线电路的电压驻波比进行检测并进行自动补偿，以维持最小驻波比
What function does the symbol VOL on the transceiver panel or in the setup menu represent?
- Avolume control, used to adjust the loudness of the receiver’s output
- Btransmit speech compression, which detects the audio input level and provides feedback control to raise the portions of the speech envelope with smaller amplitude
- Creceiver preamplifier, engaged when receiving weak signals (some specifications may be below rated values at this time)
- Dautomatic antenna tuning, which detects the voltage standing-wave ratio (SWR) of the antenna circuit and automatically compensates to maintain the minimum SWR
VOL is the universal symbol for Volume (音量), i.e. the audio output level control. Option A is correct. B describes speech compression (PROC), C the preamplifier (PRE), and D automatic antenna tuning (AT/TUNE) — all unrelated to VOL.
US–China difference: Identical labeling and meaning on US and Chinese radios.
Common pitfall: Mixing up VOL (audio output level) with RF/IF gain or SQL (squelch threshold) — turning up VOL does not improve weak-signal copy, it only makes everything louder.
Real on-air practice: On a net you keep VOL at a comfortable level and use RF gain/PRE for weak stations rather than cranking VOL into distortion.
收发信机面板上或设置菜单中的符号VOX代表什么功能？
- A发信机声控，接入后将根据对话筒有无语音输入的判别自动控制收发转换
- B自动天线调谐，对天线电路的电压驻波比进行检测并进行自动补偿，以维持最小驻波比
- C发信自动电平控制，对射频输出电平进行检测并反馈控制，以维持其在适当限度之内
- D发信语音压缩，对音频输入电平进行检测并反馈控制，以提升语音包络幅度较小的部分
What function does the symbol VOX on the transceiver panel or in the setup menu represent?
- Atransmitter voice control (VOX); once engaged, it automatically controls the transmit-receive switching based on whether there is voice input to the microphone
- Bautomatic antenna tuning, which detects the voltage standing-wave ratio (SWR) of the antenna circuit and automatically compensates to maintain the minimum SWR
- Ctransmit automatic level control (ALC), which detects the RF output level and provides feedback control to keep it within appropriate limits
- Dtransmit speech compression, which detects the audio input level and provides feedback control to raise the portions of the speech envelope with smaller amplitude
VOX stands for Voice Operated Transmit (声控 / 发信机声控). When enabled, the radio switches from receive to transmit automatically when it detects speech at the microphone, and returns to receive when speech stops — a hands-free alternative to the PTT (push-to-talk) switch. Option A is correct. B is AT/TUNE, C is ALC, D is PROC.
US–China difference: Same function and abbreviation on US and Chinese radios.
Common pitfall: Confusing VOX with PTT. VOX is automatic (voice-triggered); PTT is manual. Also do not mistake VOX for ALC/PROC which are transmit audio-processing functions.
Real on-air practice: A mobile operator driving hands-on-wheel uses VOX so he can answer a CQ call without letting go of the wheel; he sets the VOX delay so the radio returns to receive a moment after he stops talking.
既然收发信机已经具备PTT功能，那为什么有些机型还要提供VOX？
- A双手忙于其他工作时，VOX的“免提”特点有助于通联
- BVOX用于连接蓝牙耳机，提供操作的便捷性
- CVOX对话音提供更多加工处理，可有效降低发射带宽
- DVOX对话音提供更多加工处理，可使声音更易于辩识
Since the transceiver already has PTT functionality, why do some models also provide VOX?
- Awhen both hands are busy with other work, VOX’s hands-free feature helps with communication (QSO)
- BVOX is used to connect Bluetooth headsets, providing operational convenience
- CVOX provides more processing to the voice, which can effectively reduce the transmit bandwidth
- DVOX provides more processing to the voice, making the sound easier to identify
PTT (push-to-talk) requires a hand on the radio; VOX (voice-operated transmit) removes that need by keying the transmitter from speech, giving a hands-free mode. Option A states this correctly. B, C and D wrongly describe VOX as a Bluetooth link or as an audio-processing/compression function — it is neither; those are separate features (PROC/compression, Bluetooth pairing).
US–China difference: Same reason VOX exists on US radios — convenience/hands-free; no regulatory difference.
Common pitfall: Thinking VOX improves audio or narrows bandwidth. It only automates PTT; any audio processing is done by PROC/compressor, not VOX.
Real on-air practice: A cyclist or driver uses VOX so he can keep hands on the handlebars; he tunes the VOX gain and hang-time so background wind doesn’t false-key the transmitter.
某些对讲机具有发送CTCSS码的功能。缩写CTCSS指的是：
- A亚音调静噪，即从67-250.3Hz的38个亚音调频率中选取一个作为选通信号，代表38种状态之一，接收机没有收到特定的选通信号时自动关闭音频输出
- B双音多频编码，由8个音调频率中的两个频率组合成的控制信号，代表16种状态之一，用于遥控和传输数字等简单字符
- C数字设备识别码，即在松开PTT按键时自动发送一串代表设备代号的二进制数据
- D自动静噪，即在接收机没有收到信号时自动关闭音频输出
Some handheld radios have the function of sending CTCSS codes. The abbreviation CTCSS refers to:
- Asub-audible tone squelch (CTCSS): selecting one of 38 sub-audible tone frequencies from 67–250.3 Hz as a gating signal, representing one of 38 states; the receiver automatically mutes the audio output when it does not receive the specific gating signal
- Bdual-tone multi-frequency (DTMF) coding: a control signal composed of two of eight tone frequencies, representing one of 16 states, used for remote control and transmitting simple characters such as digits
- Cdigital device identification code: a string of binary data representing the device code automatically sent when the PTT key is released
- Dautomatic squelch: automatically muting the audio output when the receiver receives no signal
CTCSS (亚音调静噪 / 亚音) stands for Continuous Tone-Coded Squelch System. A low (sub-audible, 67–250.3 Hz) tone is superimposed on the voice; the receiver opens squelch only when it detects that specific tone, so stations on the same frequency using different tones do not open each other’s audio. Option A is correct. B is DTMF, C is a description closer to DCS/selcall, and D is plain carrier squelch.
US–China difference: Same CTCSS standard and 38 standard tones used in US repeaters (e.g. 100.0 Hz, 141.3 Hz); no difference.
Common pitfall: Mixing CTCSS (analog sub-audible tone) with DCS (digital code) or DTMF (touch tones for autopatch/remote). The question explicitly asks for CTCSS, so pick the analog sub-tone definition.
Real on-air practice: To use a local 2-meter repeater you set the correct CTCSS (e.g. 88.5 Hz) on transmit; the repeater only retransmits (中继转发) if it sees that tone, and your radio stays muted to other users who don’t share your tone.
某些对讲机具有发送DTMF码的功能。缩写DTMF指的是：
- A双音多频编码，由8个音调频率中的两个频率组合成的控制信号，代表16种状态之一，用于遥控和传输数字等简单字符
- B亚音调静噪，即从67-250.3Hz的38个亚音调频率中选取一个作为选通信号，代表38种状态之一，接收机没有收到特定的选通信号时自动关闭音频输出
- C数字设备识别码，即在松开PTT按键时自动发送一串代表设备代号的二进制数据
- D自动静噪，即在接收机没有收到信号时自动关闭音频输出
Some handheld radios have the function of sending DTMF codes. The abbreviation DTMF refers to:
- Adual-tone multi-frequency (DTMF) coding: a control signal composed of two of eight tone frequencies, representing one of 16 states, used for remote control and transmitting simple characters such as digits
- Bsub-audible tone squelch (CTCSS): selecting one of 38 sub-audible tone frequencies from 67–250.3 Hz as a gating signal, representing one of 38 states; the receiver automatically mutes the audio output when it does not receive the specific gating signal
- Cdigital device identification code: a string of binary data representing the device code automatically sent when the PTT key is released
- Dautomatic squelch: automatically muting the audio output when the receiver receives no signal
DTMF (双音多频) stands for Dual-Tone Multi-Frequency — the “touch tones” you hear when pressing keypad buttons. Each digit is made of one of four low tones plus one of four high tones (8 frequencies total), giving 16 combinations. It is used for remote control and sending digits, not for squelch gating. Option A is correct; B is CTCSS, C resembles DCS, D is plain squelch.
US–China difference: Same DTMF standard (the telephone keypad tones) used on US repeaters for autopatch and remote control.
Common pitfall: Confusing DTMF with CTCSS/DCS. DTMF is audible keypad tones for control; CTCSS/DCS are inaudible squelch gates you cannot hear in normal voice.
Real on-air practice: Sending DTMF digits over a repeater to open an autopatch or to a remote base station; the digits are clearly audible during the transmission.
亚音和数字亚音静噪技术都是在调频发射机所发射的语音信号上附加一个人耳不易察觉的低频信号并用来选通接收机的静噪。它们所对应的收发信机设置菜单项有：
- ACTCSS
- BDCS
- CDTMF
- DSQL
Both sub-audible-tone and digital sub-audible-tone squelch techniques add a low-frequency signal that is hard for the human ear to perceive onto the voice signal transmitted by an FM transmitter, and use it to gate the receiver’s squelch. The corresponding transceiver setup menu items are: (Choose all that apply.)
- ACTCSS
- BDCS
- CDTMF
- DSQL
“亚音” is analog CTCSS (Continuous Tone-Coded Squelch System) and “数字亚音” is DCS (Digital Coded Squelch, a digital code sent in place of the analog tone) — both are sub-audible squelch gates. The menu items for them are CTCSS and DCS, so A and B are correct. DTMF (C) is an audible dual-tone control signal, not a squelch gate; SQL (D) is the basic squelch control itself, not the “sub-tone” technique described.
US–China difference: Same: US repeaters use CTCSS and DCS (sometimes called “PL” and “DPL” after Motorola trademarks) for the identical purpose.
Common pitfall: Picking DTMF because it also involves tones — but DTMF is audible and used for control, not squelch gating. Also do not pick SQL, which is the squelch function, not the sub-tone system.
Real on-air practice: A repeater may require CTCSS on uplink; some modern repeaters use DCS instead. You select CTCSS or DCS in the menu and set the matching code to access the repeater (中继接入).
有些调频接收机的参数设置菜单有NFM和WFM两种选择。它们的含义是：
- ANFM为窄带调频方式，适用于信道带宽25kHz/12.5kHz的通信信号；WFM为宽带调频方式，适用于接收信道带宽180kHz左右的广播信号
- BNFM代表数字化语音方式，WFM代表模拟语音方式
- CNFM为调频通信本地方式（较低灵敏度），WFM为调频通信远程方式（最高灵敏度）
- DNFM为单频率守候方式，WFM为双频率守候方式
Some FM receivers have NFM and WFM options in the parameter setup menu. Their meanings are:
- ANFM is narrowband FM, suitable for communication signals with channel bandwidth 25 kHz / 12.5 kHz; WFM is wideband FM, suitable for receiving broadcast signals with channel bandwidth around 180 kHz
- BNFM stands for digital voice mode, WFM stands for analog voice mode
- CNFM is local FM communication mode (lower sensitivity), WFM is long-distance FM communication mode (highest sensitivity)
- DNFM is single-frequency standby mode, WFM is dual-frequency standby mode
NFM = narrowband FM (窄带调频), the ~5 kHz deviation, 25/12.5 kHz channel format used for two-way communication including amateur VHF/UHF. WFM = wideband FM (宽带调频), the ~75 kHz deviation, ~200 kHz channel format used for broadcast FM (88–108 MHz). Option A is correct; the others invent unrelated meanings.
US–China difference: Same terminology. Note Class A Chinese amateurs are limited to NFM (narrowband) on VHF/UHF; US Technicians similarly use NBFM on those bands.
Common pitfall: Selecting WFM to listen to an amateur repeater — you will hear distorted audio because the deviation/filter bandwidth is wrong. Use NFM for comms, WFM only for broadcast.
Real on-air practice: You set NFM to work a 145.500 MHz simplex QSO; you switch to WFM only to tune broadcast 98.5 MHz music on the same receiver.
在一些VHF/UHF业余无线电调频手持对讲机或车载电台的设置菜单中有“全频偏”和“半频偏”的选项。其意义是：
- A代表与25kHz或者12.5kHz标称发射带宽相对应的5kHz或2.5kHz调制频偏
- B同一频段内，全频偏方式下发射机的频率漂移显然是比半频偏的大一倍
- C全频偏方式适用于收发异频的中继台通信；半频偏方式适用于同频直接联络
- D全频偏方式压缩5kHz范围内的话音；半频偏方式只压缩低于2.5kHz的声音
In the setup menus of some VHF/UHF amateur FM handheld radios or mobile stations there are “full deviation” and “half deviation” options. Their meaning is:
- Arepresenting the 5 kHz or 2.5 kHz modulation deviation corresponding to the nominal transmit bandwidth of 25 kHz or 12.5 kHz
- Bwithin the same band, the transmitter’s frequency drift in full-deviation mode is obviously twice that in half-deviation mode
- Cfull-deviation mode is suitable for repeater communication with different transmit/receive frequencies; half-deviation mode is suitable for same-frequency direct contact
- Dfull-deviation mode compresses speech within 5 kHz; half-deviation mode only compresses sound below 2.5 kHz
“全频偏/半频偏” sets the FM modulation deviation (调制频偏): full deviation = 5 kHz peak for a 25 kHz channel (NBFM), half deviation = 2.5 kHz peak for a 12.5 kHz channel. The setting matches the channel spacing/bandwidth, not the frequency stability or repeater use. Option A is correct; B, C, D misattribute it to drift, repeater type, or audio compression.
US–China difference: Same concept — US narrowband mandate (12.5 kHz channels) corresponds to the half-deviation (2.5 kHz) setting.
Common pitfall: Believing full deviation improves range like raising power. It only widens the occupied bandwidth; on a 12.5 kHz channel, full deviation causes adjacent-channel interference (邻频干扰).
Real on-air practice: If another station reports your deviation is too large on a 12.5 kHz channel, switch from 全频偏 to 半频偏 (or speak farther from the mic).
如果对方报告你的调频电台发射的信号听起来失真严重，可辨度差，原因可能包括：
- A电台的电源电压不足，可以检查供电电压或更换电池模块再试
- B电台所处的位置多径衰落严重，可以挪动几步或变更频率再试
- C电台的发射频率不准。如确认这种情况，需修好设备之后再试
- D电台天线承载射频功率的能力不足，需更换高级天线之后再试
If the other station reports that your FM transmitter’s signal sounds severely distorted with poor readability, the causes may include: (Choose all that apply.)
- Athe radio’s supply voltage is insufficient; you can check the supply voltage or replace the battery module and try again
- Bthe radio is in a location with severe multipath fading; you can move a few steps or change frequency and try again
- Cthe radio’s transmit frequency is inaccurate; if confirmed, you need to repair the equipment before trying again
- Dthe antenna’s ability to handle RF power is insufficient; you need to replace it with a higher-grade antenna before trying again
Severe distortion / poor readability of your transmitted FM signal can arise from: (A) low supply voltage, which lets the PA clip and distort; (B) multipath fading at your location, which at the receiving end produces distortion and dropouts (moving or changing frequency helps); and (C) an inaccurate transmit frequency (off-frequency carrier), which the receiver demodulates off-center and distorts. D is not a cause of distortion — an under-rated antenna causes mismatch/SWR problems, not modulation distortion. Hence A, B, C are correct.
US–China difference: Same physical causes in the US; US exams likewise test power-supply and off-frequency as distortion sources.
Common pitfall: Assuming “antenna too weak” causes distortion — it does not; it causes high SWR and possible PA stress, not the characteristic off-frequency/multipath distortion described.
Real on-air practice: A handheld reports “you sound garbled”; you check the battery (low → distorting), step away from the building (multipath), and verify you are on 145.500 not 145.490 (off-frequency).
如需快速切换至你常用的某个频率，应当如何设置你的电台？
- A将该频率作为一个频道存储到电台中
- B打开哑音静噪功能
- C关闭哑音静噪功能
- D使用快速扫描功能来切换到那个频率
If you need to quickly switch to a frequency you commonly use, how should you set up your radio?
- Astore that frequency as a channel (memory channel) in the radio
- Bturn on the sub-audible-tone squelch function
- Cturn off the sub-audible-tone squelch function
- Duse the quick-scan function to switch to that frequency
To recall a favorite frequency instantly you store it in a memory channel (频道 / memory channel) and recall it with one key. Option A is correct. B/C concern CTCSS (“哑音静噪”), which is unrelated to frequency recall; D (scan) is for searching, not for instantly returning to a known frequency.
US–China difference: Same — US radios also use memory channels for quick recall.
Common pitfall: Thinking CTCSS on/off helps you “find” a frequency. It only gates squelch; it does not store or select a frequency.
Real on-air practice: You store the local 439.750 MHz repeater (with its CTCSS) in memory channel 1, so one tap returns you there instead of dialing VFO each time.
车载电台的直流电源负极应当接在哪里？
- A接到电池的负极或发动机的接地带上
- B接在天线座上
- C可以连在汽车的任意金属部件上
- D连在固定住电台的挂置架上
Where should the negative terminal of a mobile station’s DC power supply be connected?
- Ato the battery’s negative terminal or the engine’s grounding strap
- Bon the antenna connector
- Ccan be connected to any metal part of the car
- Dconnected to the bracket that holds the radio in place
The negative (ground/return) lead of a mobile radio must go to a solid, low-resistance chassis ground — directly to the battery negative post or the engine grounding strap (接地带). This gives a clean RF and DC ground. Option A is correct. B is the antenna feed (must not be grounded), and C/D are unreliable grounds that can cause RFI and voltage drop.
US–China difference: Same installation practice recommended in the US (direct to battery negative / chassis ground strap).
Common pitfall: Grounding to a random body panel or the mount bracket — high-impedance grounds cause RF feedback, alternator whine, and TX power loss.
Real on-air practice: When installing a mobile rig you run a short heavy ground strap from the radio’s negative to the battery negative to kill the engine-whine heard on transmit.
有时，装在汽车上的移动电台可能放出随引擎转速而变的尖利啸声，其来源于：
- A发电机
- B火花塞
- C电动油泵
- DABS控制器
Sometimes a mobile radio installed in a car may emit a sharp whine that varies with engine speed. Its source is:
- Athe generator (alternator)
- Bspark plugs
- Celectric fuel pump
- DABS controller
An engine-speed-dependent whine in a mobile installation is the classic signature of alternator (发电机) ripple/whine fed back through the DC power line (and sometimes radiated). The pitch tracks RPM because alternator commutation frequency is proportional to engine speed. Option A is correct. Spark-plug noise is a sharp crackle/pops, not a smooth whine; fuel pump and ABS are not RPM-synchronous tones.
US–China difference: Same cause and symptom recognized by US mobile installers; ferrite on the power lead and a good ground are the fix.
Common pitfall: Blaming spark plugs for a continuous whine. Spark-plug ignition noise is impulsive “buzz/crackle”, quite different from a steady alternator whine.
Real on-air practice: You hear a rising/falling tone as you rev the engine; adding a ferrite choke (铁氧体磁环) on the DC lead and grounding to the battery negative removes it.
如果别的业余电台报告说你的手持电台发射的FM信号的频偏过大，你应当怎么做？
- A尝试切换至NFM档位进行通联。如已使用NFM，则试着讲话时离话筒远一点儿
- B更换一块新电池再试
- C调至发射功率更大的档位
- D使用更大的声音对着话筒讲话以触发系统中隐藏的但是非常好用的语音限幅功能
If another amateur station reports that your handheld radio’s transmitted FM signal has excessive deviation, what should you do?
- Atry switching to NFM mode for communication. If already using NFM, try speaking a bit farther from the microphone
- Breplace with a new battery and try again
- Cswitch to a higher transmit power setting
- Dspeak louder into the microphone to trigger a hidden but very useful speech limiter function in the system
Excessive FM deviation (频偏过大) means your modulation swings wider than the channel allows, spreading into adjacent channels. The fix is to use the narrowband (NFM) setting if available, or reduce the audio drive by speaking farther from the mic so the limiter isn’t driven hard. Option A is correct. B (fresh battery) does not reduce deviation; C (more power) makes interference worse; D is wrong and risky — shouting over-drives the modulator.
US–China difference: Same — US Part 97 limits deviation; narrowband (≤2.5 kHz for 12.5 kHz channels) is required.
Common pitfall: Assuming a new battery or higher power fixes distortion. They don’t — deviation is set by audio level and the deviation setting, not by supply or RF power.
Real on-air practice: “Your signal is wide / splattering” → switch to NFM and back off the mic; the other station reports clean audio afterward.
如果其他电台报告说你的发射干扰了相邻频率的通信。你应当做的是：
- A检查发射机的频率指示是否准确、发射机的杂散发射指标是否合格
- B换用另一种调制模式试试看
- C将这种情况通知你的设备制造商
- D立即增加发射功率
If another station reports that your transmission is interfering with adjacent-channel communication, what you should do is:
- Acheck whether the transmitter’s frequency indication is accurate and whether the transmitter’s spurious emission指标 (spurious emission) is qualified
- Btry switching to another modulation mode
- Cnotify your equipment manufacturer of the situation
- Dimmediately increase the transmit power
Adjacent-channel interference (邻频干扰) can come from an off-frequency carrier or from excessive out-of-band / spurious emission (杂散发射) of your transmitter. The proper response is to verify the dial accuracy and that the transmitter meets its spurious-emission limits, and correct the fault. Option A is correct. Increasing power (D) worsens interference; switching mode (B) or calling the maker (C) does not address the root cause. This ties to the obligation to avoid harmful interference (有害干扰) under the Radio Regulations of the PRC.
US–China difference: Same duty in the US — FCC Part 97 requires you not cause harmful interference and to fix a non-conforming transmitter.
Common pitfall: Raising power to “override” the neighbor — this is both wrong and a rules violation; you must reduce or fix your emission instead.
Real on-air practice: A neighbor on 145.500 says you bleed onto 145.525; you check your display calibration and run a spur check, then repair the radio.
如果其他电台报告说你在2米波段的信号本来很强，但是突然就变弱甚至难以辨别了，你应当怎么做？
- A稍稍移动一下自己的位置。电波传播的多径效应会时而引起信号衰落或解调失真
- B打开发射机的亚音静噪功能
- C请对方电台检查一下静噪设置
- D将你电台中的锂电池换成镍氢的
If another station reports that your signal on the 2-meter band was originally strong but suddenly became weak or even hard to distinguish, what should you do?
- Amove your position slightly. The multipath effect of radio propagation can sometimes cause signal fading or demodulation distortion
- Bturn on the transmitter’s sub-audible-tone squelch function
- Cask the other station to check its squelch setting
- Dreplace the Li-ion battery in your radio with a NiMH one
On VHF (the 2-meter band / 144 MHz), signals are often line-of-sight and subject to multipath (多径效应): reflected paths combine destructively, causing rapid fading (衰落) and distortion. Moving a few steps changes the path geometry and restores the signal — a standard VHF technique. Option A is correct. B (CTCSS) only gates squelch, C is the other station’s setting, D (battery chemistry) is unrelated.
US–China difference: Same VHF multipath behavior on US 2-meter FM; “take a few steps” is universal advice.
Common pitfall: Thinking the radio or battery failed. It is propagation (multipath null), not equipment — moving fixes it instantly.
Real on-air practice: “You faded out” on a 146 MHz QSO → you step around the corner of the building and the signal returns strong.
如果进行SSB或CW通联时周边环境嘈杂，哪种设备可以替代电台上的扬声器，改善话音抄收？
- A耳机
- B低通滤波器
- C视频显示器
- D吊杆胖话筒
If the surroundings are noisy during SSB or CW communication (QSO), which device can replace the radio’s speaker to improve copying of the voice?
- Aheadphones
- Blow-pass filter
- Cvideo display
- Dboom microphone
A headphone (耳机) blocks ambient room noise and couples the received audio directly to the ear, dramatically improving the ability to copy (抄收) weak SSB/CW in a noisy environment. Option A is correct. A low-pass filter (B) is an RF/audio component, not a listening device; a video display (C) and boom mic (D) do not help receiving.
US–China difference: Same — headphones are the standard copy aid in US contesting and CW work.
Common pitfall: Thinking a boom mic (transmitting accessory) improves receiving. It does not; only the listening device (headphones) helps copying.
Real on-air practice: In a noisy shack during a CW contest you put on closed-back headphones to pull weak “599” reports out of the noise.
全功能小型收发信机的面板上常有缩写为“NB”和“SQL”的功能，它们有什么不同？
- ANB为“抑噪”，切除高于平均信号的大幅度突发脉冲噪声；SQL为“静噪”，信噪比达不到一定水平时自动关闭音频输出
- BNB和SQL都是指“抑噪”，收不到有用信号时自动关断背景噪声
- CNB和SQL都是指“静噪”，切除高于平均信号的大幅度突发脉冲噪声
- DNB和SQL都是指“静噪”，收不到带有预期的特定控制信号时自动关断音频输出
Full-featured small transceivers often have functions abbreviated “NB” and “SQL” on the panel. What is the difference between them?
- ANB is “noise blanking”, which cuts off large-amplitude burst impulse noise above the average signal; SQL is “squelch”, which automatically mutes the audio output when the signal-to-noise ratio does not reach a certain level
- BNB and SQL both refer to “noise blanking”, automatically cutting off background noise when no useful signal is received
- CNB and SQL both refer to “squelch”, cutting off large-amplitude burst impulse noise above the average signal
- DNB and SQL both refer to “squelch”, automatically cutting off the audio output when the expected specific control signal is not received
NB = Noise Blanking (抑噪): it detects short, high-amplitude impulse spikes (e.g. from automobile ignition) and blanks them for a few microseconds. SQL = Squelch (静噪): it mutes the audio entirely when the signal is below a threshold. They are distinct functions. Option A states both correctly; B, C, D wrongly merge them or swap their definitions.
US–China difference: Same NB vs SQL distinction on US transceivers.
Common pitfall: Treating NB and SQL as the same. NB removes impulse spikes within a received signal; SQL simply opens/closes the audio gate. Turning up squelch will not remove ignition crackle.
Real on-air practice: Near a busy road you enable NB to kill the “pop-pop” of traffic, while keeping SQL set so the radio stays quiet between QSOs.
某些车辆的火花塞辐射脉冲干扰。这可能导致收信机的AGC过早起控，使正在接收的SSB或CW信号受到压制，进而影响听抄。遇到这种情况，你应当如何设置你的电台？
- A打开电台的抑噪（NB）功能
- B降低静噪（SQL）阀值
- C将频率稍稍调偏一点儿
- D反复调节电台的RIT旋钮
Some vehicles’ spark plugs radiate impulse interference. This may cause the receiver’s AGC to act too early, suppressing the SSB or CW signal being received and thus affecting copying. In this situation, how should you set your radio?
- Aturn on the radio’s noise blanking (NB) function
- Blower the squelch (SQL) threshold
- Ctune the frequency slightly off
- Drepeatedly adjust the radio’s RIT knob
Spark-plug impulse noise is a burst of sharp spikes. The noise blanker (NB / 抑噪) is specifically designed to detect and clip these impulses before they reach the AGC and audio, preventing the AGC from pumping the desired SSB/CW signal down. Option A is correct. Lowering squelch (B) only opens the audio gate wider (more noise); tuning off (C) or RIT (D) does not remove impulse noise.
US–China difference: Same NB remedy for ignition/impulse noise on US gear.
Common pitfall: Raising or lowering SQL to fight impulse noise — squelch cannot remove spikes riding on a present carrier; only NB (or a noise limiter) helps.
Real on-air practice: Parked next to a running car, CW copy breaks up; you switch on NB and the ignition “buzz” disappears, restoring the “599” report.
全功能小型收发信机面板上的“MODE”代表什么功能：
- A用来切换工作方式，比如FM、LSB、USB和CW等
- B用来切换静噪方式，比如CTCSS和DCS等
- C用来切换接收机的工作方式，比如射频直采和低中频超外差等
- D用来切换监听方式，比如单耳音频、双耳音频和CW立体声等
What function does “MODE” on the panel of a full-featured small transceiver represent?
- Aused to switch the operating mode, such as FM, LSB, USB, and CW, etc.
- Bused to switch the squelch mode, such as CTCSS and DCS, etc.
- Cused to switch the receiver’s operating mode, such as direct RF sampling and low-IF superheterodyne, etc.
- Dused to switch the monitoring mode, such as mono audio, binaural audio, and CW stereo, etc.
MODE selects the emission/operating mode (工作方式) — FM, AM, SSB (LSB/USB), CW, RTTY, etc. Option A is correct. Squelch modes (B) are set elsewhere (CTCSS/DCS menus); receiver architecture (C) and audio monitoring (D) are not what the MODE knob does.
US–China difference: Identical “MODE” function on US transceivers.
Common pitfall: Setting MODE to FM when working a CW/SSB station — you will hear nothing or just a tone; match the mode to the other station.
Real on-air practice: Answering a CQ on 14.070 MHz you select “USB” (or DATA/RTTY) in MODE; on 145.500 MHz FM you select “FM”.
收发信机面板上的符号ATT代表什么功能？
- A收信机输入衰减器，在接收大信号时接入，使信号不致过大而使前级电路过载
- B自动天线调谐，对天线电路的电压驻波比进行检测并进行自动补偿，以维持最小驻波比
- C发信自动电平控制，对射频输出电平进行检测并反馈控制，以维持其在适当限度之内
- D发信自动音量控制，对音频输入电平进行检测并反馈控制，以维持其在适当限度之内
What function does the symbol ATT on the transceiver panel represent?
- Areceiver input attenuator, engaged when receiving strong signals so that the signal does not become too large and overload the front-end circuit
- Bautomatic antenna tuning, which detects the voltage standing-wave ratio (SWR) of the antenna circuit and automatically compensates to maintain the minimum SWR
- Ctransmit automatic level control (ALC), which detects the RF output level and provides feedback control to keep it within appropriate limits
- Dtransmit automatic volume control, which detects the audio input level and provides feedback control to keep it within appropriate limits
ATT = input attenuator (衰减器), a switchable pad at the receiver front end that reduces a very strong incoming signal so the first stages do not overload (过载/阻塞). Option A is correct. B is AT/TUNE, C is ALC, D is transmit audio AVC.
US–China difference: Same ATT function on US receivers; often paired with an “RF gain” or “ATT” button.
Common pitfall: Confusing ATT (receive attenuation) with ALC (transmit level control) or AT (antenna tuner). ATT only reduces incoming signal strength.
Real on-air practice: Working a huge broadcast station next to your 40 m frequency, you switch ATT in to keep the front end from blocking your weak CW partner.
收发信机面板上的符号AGC代表什么功能？
- A收信机自动增益控制，对中频级信号电平进行检测并反馈控制，防止电路过载
- B收信自动音量控制，对音频输出电平进行检测并反馈控制，以维持其在适当限度之内
- C自动天线调谐，对天线电路的电压驻波比进行检测并进行自动补偿，以维持最小驻波比
- D发信自动电平控制，对射频输出电平进行检测并反馈控制，以维持其在适当限度之内
What function does the symbol AGC on the transceiver panel represent?
- Areceiver automatic gain control, which detects the IF-stage signal level and provides feedback control to prevent circuit overload
- Breceiver automatic volume control, which detects the audio output level and provides feedback control to keep it within appropriate limits
- Cautomatic antenna tuning, which detects the voltage standing-wave ratio (SWR) of the antenna circuit and automatically compensates to maintain the minimum SWR
- Dtransmit automatic level control (ALC), which detects the RF output level and provides feedback control to keep it within appropriate limits
AGC = Automatic Gain Control (自动增益控制). In a receiver it samples the IF/Detection level and adjusts the gain so strong and weak stations come out at a steady audio level and the stages don’t overload. Option A is correct. B describes audio AVC (not the standard AGC definition), C is AT/TUNE, D is transmit ALC.
US–China difference: Same AGC concept and abbreviation on US receivers.
Common pitfall: Thinking AGC controls volume. It controls RF/IF gain to keep level constant; volume is set separately. Also don’t confuse AGC (receive) with ALC (transmit).
Real on-air practice: As a DX station’s signal fades, AGC keeps the audio at listenable level instead of disappearing into the noise.
既然全功能收信机具有AGC功能，那为什么好多机型还要装设衰减（ATT）开关？
- A特强带外信号可以阻塞接收机的前级电路，致使器件非线性工作，产生失真和互调。此时需在接收机的前端电路之前加入衰减器，并用开关控制其切入与否
- B通常，增益控制旋钮的控制范围不够宽，加入ATT开关可以拓展增益控制范围
- C如果遭遇特强带内干扰，那么打开ATT就可防止过大的音量损坏扬声器或耳机了
- D这可以防止本台发射机的强信号损坏本台的接收机电路
Since full-featured receivers have AGC, why do many models also have an attenuator (ATT) switch?
- Aan extremely strong out-of-band signal can block the receiver’s front-end circuit, causing the device to operate nonlinearly and produce distortion and intermodulation. In this case an attenuator must be added before the receiver’s front-end circuit, with a switch controlling whether it is engaged
- Busually the gain control knob’s range is not wide enough; adding the ATT switch can extend the gain control range
- Cif encountering extremely strong in-band interference, turning on ATT prevents excessive volume from damaging the speaker or headphones
- Dthis can prevent the strong signal of this station’s transmitter from damaging this station’s receiver circuit
AGC only acts after the front-end amplifier; a very strong signal that arrives before the AGC-controlled stages can drive the first mixer/RF amp into nonlinear operation, causing blocking, cross-modulation and intermodulation (互调). The ATT pad sits ahead of that stage and tames the strong signal before it overloads the front end. Option A is correct. B (gain range), C (speaker protection), D (TX self-damage) are not the real reason.
US–China difference: Same design rationale on US HF rigs; ATT is standard ahead of the first mixer.
Common pitfall: Believing AGC alone protects the front end. AGC cannot fix overload that occurs before its controlled stage; that’s why ATT exists.
Real on-air practice: Near a broadcast bander on 7 MHz you switch ATT in so the strong AM splatter doesn’t desense your 7.050 MHz SSB receive.
关于接收机的“过载”现象，以下描述正确的是：
- A输入信号过于强大以至机内电路饱和阻塞，严重时会损坏接收机前端电路的元器件
- B启用接收机的ATT功能可消除或缓解过载
- C接收机消耗的电流过大，致使电源出现过载现象。情况严重时供电装置会烧毁
- D减小接收机的喇叭音量，可缓解过载现象
Regarding the receiver “overload” phenomenon, which of the following descriptions is correct? (Choose all that apply.)
- Athe input signal is so strong that the internal circuitry saturates and blocks; in severe cases it can damage components in the receiver front-end
- Benabling the receiver’s ATT function can eliminate or relieve overload
- Cthe receiver consumes too much current, causing the power supply to overload; in severe cases the power supply can burn out
- Dreducing the receiver’s speaker volume can relieve the overload phenomenon
Receiver overload (过载/阻塞) means an excessively strong input drives the front-end stages into saturation/blocking, which can even damage components; engaging the input attenuator (ATT) reduces the drive and cures or relieves it. So A and B are correct. C describes a power-supply overload, a different thing; D — turning down the speaker volume does nothing to the RF overload, since the overload happens before the audio stage.
US–China difference: Same overload definition and ATT remedy in US equipment.
Common pitfall: Thinking lowering the volume fixes overload. Volume is downstream; the overload is in the RF/IF front end, so only ATT (or less gain/IP3 mitigation) helps.
Real on-air practice: A strong local on 14.200 MHz blocks your 14.070 MHz contact; flipping ATT in restores copy.
应关闭接收机AGC功能的情况是：
- A有用微弱信号和强干扰同时出现时
- B接收微弱信号时
- C接收特强信号时
- D有用强信号中夹杂着微弱干扰
The situation in which the receiver’s AGC function should be turned off is:
- Awhen a useful weak signal and a strong interference appear simultaneously
- Bwhen receiving a weak signal
- Cwhen receiving an extremely strong signal
- Dwhen a useful strong signal is mixed with weak interference
When a weak desired signal coexists with a strong interferer, AGC tracks the strong signal and turns the receiver gain down, pulling the weak signal even further into the noise — so you disable AGC (or use a fast/separate scheme) to keep the weak signal audible. Option A is correct. For a plain weak signal (B) or strong signal (C) AGC normally helps; D is not the classic case for disabling it.
US–China difference: Same — US operators switch AGC off or to “fast/manual” when a strong carrier masks a weak one.
Common pitfall: Leaving AGC on by default and wondering why a weak station vanishes next to a strong one. Recognize the “AGC pumping” scenario and turn it off.
Real on-air practice: A strong broadcaster sits beside your weak CW contact; you set AGC off and manually adjust RF gain to keep the weak “599”-class signal readable.
应选择较短的AGC时间常数的情况是：
- A接收FM/FSK/PSK等包络幅度恒定的信号
- B接收SSB和AM等正常信号的包络幅度不断变化的信号
- C将接收机应用于“比幅度法规”测向时
- D有用微弱信号和强干扰同时出现时
The situation in which a shorter AGC time constant should be selected is:
- Areceiving signals with constant envelope amplitude such as FM/FSK/PSK
- Breceiving signals whose envelope amplitude keeps changing, such as normal SSB and AM
- Cwhen applying the receiver to “amplitude-comparison” direction finding
- Dwhen a useful weak signal and strong interference appear simultaneously
For constant-envelope signals (FM, FSK, PSK) the carrier amplitude is steady, so a short AGC time constant keeps the level tightly regulated without “pumping” the audio. Option A is correct. SSB/AM (B) have a varying voice envelope, so a long time constant is used to avoid breathing/distortion; C and D are unrelated to the constant-envelope rule.
US–China difference: Same AGC time-constant guidance on US transceivers (often “Fast” for FM/digital, “Slow” for SSB).
Common pitfall: Using a long AGC on FM — the audio level then lags and sounds “swishy”; FM wants fast AGC. Conversely, fast AGC on SSB makes the voice “pump”.
Real on-air practice: Switching from 14.070 MHz USB (slow AGC) to 145.500 MHz FM (fast AGC) gives clean, steady FM audio.
应选择较长的AGC时间常数的情况是：
- A接收SSB和AM等正常信号的包络幅度不断变化的信号
- B接收FM/FSK/PSK等包络幅度恒定的信号遇到变化很快的传播衰落时
- C将接收机应用于“比幅度法规”测向时
- D有用微弱信号和强干扰同时出现时
The situation in which a longer AGC time constant should be selected is:
- Areceiving signals whose envelope amplitude keeps changing, such as normal SSB and AM
- Breceiving FM/FSK/PSK constant-envelope signals encountering fast-changing propagation fading
- Cwhen applying the receiver to “amplitude-comparison” direction finding
- Dwhen a useful weak signal and strong interference appear simultaneously
SSB and AM voice have a continuously varying envelope; a long AGC time constant averages it out so the audio volume stays steady instead of “pumping” with every syllable. Option A is correct. Constant-envelope FM/FSK/PSK (B) want short AGC; C (DF) and D are not the envelope-variation case.
US–China difference: Same “slow AGC for SSB/AM” rule on US rigs.
Common pitfall: Setting fast AGC on SSB — the voice then swells and dips unnaturally (“breathing”). Use slow AGC for SSB/AM.
Real on-air practice: On 7.050 MHz LSB you use “Slow” AGC so the other op’s “599” report comes through at even volume despite pauses in speech.
多数小型全功能收发信机的面板上都可以看到符号PRE，其代表什么功能？
- A收信机前置放大器，在接收微弱信号时接入（此时某些技术指标可能低于额定值）
- B自动天线调谐，对天线电路的电压驻波比进行检测并进行自动补偿，以维持最小驻波比
- C发信自动电平控制，对射频输出电平进行检测并反馈控制，以维持其在适当限度之内
- D发信语音压缩，对音频输入电平进行检测并反馈控制，以提升语音包络幅度较小的部分
On most small full-featured transceivers you can see the symbol PRE on the panel. What function does it represent?
- Areceiver preamplifier, engaged when receiving weak signals (some specifications may be below rated values at this time)
- Bautomatic antenna tuning, which detects the voltage standing-wave ratio (SWR) of the antenna circuit and automatically compensates to maintain the minimum SWR
- Ctransmit automatic level control (ALC), which detects the RF output level and provides feedback control to keep it within appropriate limits
- Dtransmit speech compression, which detects the audio input level and provides feedback control to raise the portions of the speech envelope with smaller amplitude
PRE = receiver preamplifier (前置放大器 / LNA), a low-noise amplifier at the front end that boosts weak signals. Option A is correct. B is AT/TUNE, C is ALC, D is PROC/compression.
US–China difference: Same PRE (preamp) function and abbreviation on US transceivers.
Common pitfall: Leaving the preamp on in strong-signal or noisy environments — it can raise the noise floor and worsen strong-signal handling; it helps most for weak-signal DX, not local comms.
Real on-air practice: Chasing a weak 20 m DX station you switch PRE on; for a loud local you turn it off to reduce desensitization.
收发信机面板上的符号ALC代表什么功能？
- A发信自动电平控制，对射频输出电平进行检测并反馈控制，以维持其在适当限度之内
- B发信自动音量控制，对音频输入电平进行检测并反馈控制，以维持其在适当限度之内
- C自动天线调谐，对天线电路的电压驻波比进行检测并进行自动补偿，以维持最小驻波比
- D自动频率控制，对发射频率的漂移进行检测并反馈控制，以维持准确的工作频率
What function does the symbol ALC on the transceiver panel represent?
- Atransmit automatic level control, which detects the RF output level and provides feedback control to keep it within appropriate limits
- Btransmit automatic volume control, which detects the audio input level and provides feedback control to keep it within appropriate limits
- Cautomatic antenna tuning, which detects the voltage standing-wave ratio (SWR) of the antenna circuit and automatically compensates to maintain the minimum SWR
- Dautomatic frequency control, which detects the drift of the transmit frequency and provides feedback control to maintain the accurate operating frequency
ALC = Automatic Level Control (自动电平控制) on the transmit side: it samples the RF output and feeds back to the driver stage to keep PEP/RF output from over-driving the final amplifier, preventing distortion and damage. Option A is correct. B is audio AVC; C is AT/TUNE; D is AFC.
US–China difference: Same ALC meaning on US transmitters; the ALC meter should ride just into the indicated region, not pinned.
Common pitfall: Confusing ALC (transmit RF level) with audio gain/compression. ALC limits RF; mic gain sets drive. Over-driving still occurs if mic gain is too high even with ALC active (see U0419).
Real on-air practice: On SSB you adjust mic gain so the ALC needle just dips on peaks — clean signal, full PEP.
在单边带发信机中，发信自动电平控制（ALC）的主要作用是：
- A防止过驱动导致调制失真或引发电路故障
- B改善发信机的频率稳定度
- C自动实现天线电路的阻抗匹配
- D防止话筒过于灵敏带来背景噪声
In an SSB transmitter, what is the main function of transmit automatic level control (ALC)?
- Aprevent over-driving from causing modulation distortion or triggering circuit faults
- Bimprove the transmitter’s frequency stability
- Cautomatically achieve impedance matching of the antenna circuit
- Dprevent the microphone from being too sensitive and bringing background noise
In an SSB transmitter, ALC limits the drive to the final amplifier so speech peaks do not over-drive it (which would cause splatter/distortion and possible damage). Option A is correct. Frequency stability (B) is set by the oscillator/synthesizer; matching (C) is the tuner; background noise (D) is a mic-gain issue.
US–China difference: Same ALC purpose on US SSB transmitters.
Common pitfall: Believing ALC keeps the frequency stable or matches the antenna. It only controls RF drive level; those are separate subsystems.
Real on-air practice: During a contest you keep ALC just engaged on voice peaks so you run full legal PEP without splattering onto adjacent channels.
业余电台进行单边带话音通信时，如果对方反映虽然己方的讲话基本可辨，但是在话音的间隙中夹杂嘈杂的背景噪声。这时应当：
- A调低发射机的话筒增益。如果发射机带有语音压缩处理功能，则应尝试调低控制深度
- B调低发射机的射频输出功率
- C调整发射机的天线匹配电路
- D调整发射机的ALC控制深度
When an amateur station conducts SSB voice communication, if the other party reports that although your speech is basically recognizable, noisy background noise is mixed in the gaps of the voice, you should:
- Alower the transmitter’s microphone gain. If the transmitter has speech compression processing, try lowering the control depth
- Blower the transmitter’s RF output power
- Cadjust the transmitter’s antenna matching circuit
- Dadjust the transmitter’s ALC control depth
Background noise heard in the speech gaps means the mic is too sensitive and is picking up room noise during pauses (and/or the compressor is boosting it). Lowering mic gain, and reducing compressor (PROC) depth if present, raises the noise floor relative to speech so the gaps quieten. Option A is correct. Power (B), antenna matching (C), and ALC depth (D) do not address room noise in the gaps.
US–China difference: Same fix on US SSB rigs — reduce mic gain / compression when the other station hears your room noise.
Common pitfall: Turning down RF power to fix background noise — that only shortens your range; the noise in the gaps is a microphone/gain problem, not power.
Real on-air practice: “I hear your fan/room between words” → you lower mic gain a notch and ease the processor; the other op reports clean audio.
即使打开了发射机的ALC，将话筒的增益调得过高仍可能导致：
- A发出的信号失真
- B发射机的功率提升
- C发射机的频率漂移变大
- D天线的驻波比增加
Even with the transmitter’s ALC turned on, setting the microphone gain too high can still lead to:
- Athe transmitted signal becoming distorted
- Bthe transmitter’s power increasing
- Cthe transmitter’s frequency drift increasing
- Dthe antenna’s standing-wave ratio increasing
ALC limits the average RF drive but cannot perfectly clean up a severely over-driven speech waveform — excessive mic gain still flattens/clips the audio (distortion) before ALC can fully compensate, producing splatter. Option A is correct. Over-gain does not raise power (B, ALC caps it), change frequency stability (C), or alter SWR (D, which is set by the antenna).
US–China difference: Same — US propagation/clean-signal advice: set mic gain so ALC only dips on peaks.
Common pitfall: Assuming “ALC is on, so I can crank the mic” — over-driving still distorts the signal and causes out-of-band splatter (harmful interference).
Real on-air practice: “You’re distorted/splattering” even though your ALC light is on → back off mic gain; the ALC was railing, not regulating.
为什么使用单边带收发信机发送AFSK信号时需要关闭ALC？
- AALC增加AFSK信号的失真，抬升误码率
- BALC使发射功率失控，导致发射机故障
- CALC使信号的极性反转，致使无法解码
- DALC影响AFSK信号的频响，使音色变差
Why is it necessary to turn off ALC when sending AFSK signals with an SSB transceiver?
- AALC increases the distortion of the AFSK signal, raising the bit error rate
- BALC causes the transmit power to run out of control, leading to transmitter failure
- CALC reverses the polarity of the signal, making it undecodable
- DALC affects the frequency response of the AFSK signal, worsening the timbre
AFSK (Audio Frequency Shift Keying, e.g. for RTTY/PSK) is a constant-data tone pair whose envelope must stay clean. The speech-derived ALC loop was designed for voice and will pump/limit the AFSK envelope, distorting the shift and raising the bit error rate (误码率, BER). So ALC is disabled for data. Option A is correct. B (power runaway), C (polarity reversal) and D (timbre) are not the issue.
US–China difference: Same digital-mode practice in the US — disable ALC/processing and often use a fixed drive for RTTY/PSK.
Common pitfall: Leaving speech compression or ALC on for data modes. It wrecks the constellation/envelope and the other station cannot decode; set a clean, unprocessed drive.
Real on-air practice: For an RTTY contact you switch the rig to “DATA” (ALC/PROC off) and set a steady audio drive so the other op’s decoder locks with a low BER.
单边带发信机的语音压缩功能有什么作用？
- A压低较强语音信号的幅度、提升较弱信号的幅度，改善较弱的语音在接收端的信噪比
- B压低较弱语音信号的幅度、提升较强信号的幅度，增加语音的动态范围和抑扬顿挫感
- C压低语音信号的低频分量，提升高频分量，增加信号的带宽，使高音更加细腻
- D压缩信号所占用的频谱宽度，提高无线电频谱的利用率
What is the function of the speech compression feature in an SSB transmitter?
- Acompress the amplitude of stronger speech signals and raise that of weaker signals, improving the SNR of weaker speech at the receiving end
- Blower the amplitude of weaker speech and raise that of stronger signals, increasing the dynamic range and intonation of the speech
- Clower the low-frequency components of the speech signal, raise the high-frequency components, increase the signal bandwidth, making the treble more delicate
- Dcompress the spectrum width occupied by the signal, improving the utilization of the radio spectrum
Speech compression (语音压缩 / speech processing) reduces the peaks and lifts the troughs of the voice waveform so the average level — and thus the perceived loudness/SNR at the far end — is higher without exceeding the ALC limit. Option A is correct. B is the opposite (it reduces dynamic range, not increases it usefully); C is equalization, not compression; D is untrue — compression does not shrink occupied bandwidth and can even widen it if overdone.
US–China difference: Same compressor purpose on US SSB rigs; “processing” is a popular contest feature.
Common pitfall: Believing compression narrows bandwidth or that “more compression = better”. Over-compression adds splatter (harmful interference) and distortion.
Real on-air practice: In a phone contest you add mild compression so your “599” report carries better through QRM, while keeping it light to avoid splatter.
收发信机面板上的符号PROC代表什么功能？
- A发信语音压缩，对音频输入电平进行检测并反馈控制，以使包络幅度较小语音获得提升
- B收信机前置放大器，在接收微弱信号时接入（此时某些技术指标可能低于额定值）
- C自动天线调谐，对天线电路的电压驻波比进行检测并进行自动补偿，以维持最小驻波比
- D发信自动电平控制，对射频输出电平进行检测并反馈控制，以维持其在适当限度之内
What function does the symbol PROC on the transceiver panel represent?
- Atransmit speech compression, which detects the audio input level and provides feedback control to boost speech with smaller envelope amplitude
- Breceiver preamplifier, engaged when receiving weak signals (some specifications may be below rated values at this time)
- Cautomatic antenna tuning, which detects the voltage standing-wave ratio (SWR) of the antenna circuit and automatically compensates to maintain the minimum SWR
- Dtransmit automatic level control (ALC), which detects the RF output level and provides feedback control to keep it within appropriate limits
PROC = speech processor/compression (语音压缩) on transmit. It boosts low-level speech so the average modulation is higher. Option A is correct. B is PRE, C is AT/TUNE, D is ALC.
US–China difference: Same PROC/processor function and label on US transceivers.
Common pitfall: Confusing PROC (transmit speech boost) with PRE (receive preamp) or ALC (RF level limit). They are three different blocks.
Real on-air practice: You toggle PROC on for a weak-contact SSB QSO to make your audio “punchier”, then off for data modes.
发信时，若话音压缩调整不当可能带来什么问题?
- A可能产生很多互调成分，影响对方收信时的辨识度
- B可能使话音严重失真，但是不影响对方电台的收信
- C可能发射很大的交流声
- D可能使话筒过载损坏
When transmitting, what problem may improper adjustment of speech compression cause?
- Ait may produce many intermodulation components, affecting the identifiability at the other station’s receiver
- Bit may severely distort the voice, but does not affect the other station’s reception
- Cit may transmit a large hum
- Dit may overload and damage the microphone
Over-driving the speech processor generates heavy harmonics and intermodulation products (互调成分) that spread outside the channel, degrading the other station’s ability to copy you and causing adjacent-channel interference. Option A is correct. B is wrong (distortion does hurt copy); C (hum) is a ground/PSR issue, not compression; D — a processor will not damage the mic.
US–China difference: Same hazard — over-processing splatters and is a clean-signal violation under FCC Part 97 too.
Common pitfall: Assuming “more compression = louder = better”. Excessive depth creates IMD/splatter that masks you and annoys neighbors.
Real on-air practice: “You’re wide/hashy” → ease the PROC level; the splatter on adjacent frequencies disappears and your “599” reads clearly.
为什么用单边带收发信机发送AFSK信号时应关闭语音压缩功能？
- A语音压缩可能导致信号的包络畸变，破坏基带特征，抬升误码率
- B经语音压缩处理的信号，其相位变化已不存在，本质上无法解码
- C经语音压缩处理的信号，其幅度变化已不存在，本质上无法解码
- D语音压缩提升信号的峰均比，易导致发射机功率放大器过热损坏
Why should the speech compression function be turned off when sending AFSK signals with an SSB transceiver?
- Aspeech compression may cause envelope distortion of the signal, destroying the baseband characteristics and raising the bit error rate
- Bafter speech compression, the phase variation of the signal no longer exists, making it essentially undecodable
- Cafter speech compression, the amplitude variation of the signal no longer exists, making it essentially undecodable
- Dspeech compression raises the peak-to-average ratio of the signal, easily causing the transmitter power amplifier to overheat and be damaged
AFSK data tones need a clean, stable envelope; speech compression reshapes/limits that envelope, distorting the mark/space transitions (baseband) and raising the bit error rate (误码率). Hence compression must be off for data. Option A is correct. B and C are false (compression doesn’t remove phase or all amplitude); D is backwards — compression lowers peak-to-average, not raises it dangerously.
US–China difference: Same — US digital-mode guides say disable speech processing/compression and often ALC for clean RTTY/PSK.
Common pitfall: Leaving the processor on for a digital mode “to be louder”. It garbles the data; the decoder shows a high BER or no decode.
Real on-air practice: Before a PSK31 QSO you switch to the DATA mode (PROC/ALC off) so the waterfall shows clean tones and the other station decodes instantly.
业余电台以发射的方法测量发射功率和天线驻波比时必须留意并做到的是：
- A先将频率设置到无人使用的空闲频率、偏离常用的热点频率
- B先将天线的发射方向指向正北
- C先将收发信机的语音压缩功能打开
- D话筒离嘴距离在2公分以上，电键按键时间不短于5秒钟
When an amateur station measures transmit power and antenna SWR by transmitting, what must be noted and done is:
- Afirst set the frequency to an unused idle frequency, away from commonly used hot-spot frequencies
- Bfirst point the antenna’s transmit direction due north
- Cfirst turn on the transceiver’s speech compression function
- Dkeep the microphone more than 2 cm from the mouth, and the key-down time no shorter than 5 seconds
Measuring by actually transmitting radiates a signal, so to avoid causing harmful interference (有害干扰) you must do it on a clear, unused frequency away from busy calling/simplex frequencies. Option A is correct. B (point north) is irrelevant; C (turn on compression) is wrong for a clean carrier measurement; D’s specifics are not the required rule.
US–China difference: Same courtesy/duty in the US — test on a clear frequency; US band plans mark certain frequencies for testing, but you still avoid active QSOs.
Common pitfall: Testing SWR on a popular calling frequency (e.g. 145.000 / 14.270 MHz) and walking on an ongoing contact. Pick a clear spot.
Real on-air practice: You tune to a quiet 144.600 MHz segment (not the 145.000 calling freq) to key up and read your SWR meter.
单边带业余电台测试检查天线驻波比需要发射平稳的连续信号。文明的作法是：
- A将电台设为CW方式并按下电键。或者，将电台设为AM或FM方式并按下PTT键（不对话筒说话）以产生连续载波。测试结束后设回SSB方式
- B将电台设为SSB方式，用平稳的气流对话筒吹口哨
- C将电台设为SSB方式，深呼吸后用平稳的气流对话筒发长音“啊”
- D将电台设为SSB方式，深呼吸后用平稳的气流对话筒发长音“嘻”
An SSB amateur station needs to transmit a steady continuous signal to test and check the antenna SWR. The courteous way to do it is:
- Aset the radio to CW mode and press the key. Alternatively, set the radio to AM or FM mode and press the PTT (without speaking into the microphone) to produce a continuous carrier. After the test, set it back to SSB mode
- Bset the radio to SSB mode and whistle into the microphone with a steady breath
- Cset the radio to SSB mode, take a deep breath and emit a long “ah” sound into the microphone with steady breath
- Dset the radio to SSB mode, take a deep breath and emit a long “xi” sound into the microphone with steady breath
To measure SWR you need an unmodulated (or steady) carrier, not voice. The courteous method is CW key-down, or AM/FM with PTT held but silent (no speech), giving a clean continuous carrier, then return to SSB. Option A is correct. Whistling or voicing (B/C/D) sends modulated, intelligible — and thus potentially interfering — audio onto the air, which is neither clean nor courteous.
US–China difference: Same courtesy rule in the US — use a CW carrier or unmodulated FM/AM, never talk or whistle, during SWR checks.
Common pitfall: Keying the mic and talking/whistling to “hold a carrier” — that radiates recognizable audio and can be heard/recorded by others; use CW or silent PTT instead.
Real on-air practice: You switch to CW, press the key for a few seconds to read the SWR bridge, then release and go back to SSB — no one hears anything but a brief carrier.
收发信机面板上的符号AT或者TUNE代表什么功能？
- A自动天线调谐，对天线电路的电压驻波比进行检测并进行自动补偿，以维持最小驻波比
- B发信自动音量控制，对音频输入电平进行检测并反馈控制，以维持其在适当限度之内
- C发信自动电平控制，对射频输出电平进行检测并反馈控制，以维持其在适当限度之内
- D自动频率控制，对发射频率的漂移进行检测并反馈控制，以维持准确的工作频率
What function do the symbols AT or TUNE on the transceiver panel represent?
- Aautomatic antenna tuning, which detects the voltage standing-wave ratio (SWR) of the antenna circuit and automatically compensates to maintain the minimum SWR
- Btransmit automatic volume control, which detects the audio input level and provides feedback control to keep it within appropriate limits
- Ctransmit automatic level control (ALC), which detects the RF output level and provides feedback control to keep it within appropriate limits
- Dautomatic frequency control, which detects the drift of the transmit frequency and provides feedback control to maintain the accurate operating frequency
AT / TUNE = automatic antenna tuner (自动天线调谐): it matches the transmitter to the antenna by sensing the SWR and adjusting a matching network for the lowest SWR. Option A is correct. B is transmit AVC; C is ALC; D is AFC.
US–China difference: Same AT/TUNE tuner function on US transceivers; many US rigs have a built-in tuner.
Common pitfall: Confusing TUNE (antenna matching) with ALC (RF level) or AFC (frequency). The tuner changes the feedline match, not the audio or frequency.
Real on-air practice: On 18 MHz with a non-resonant wire you hit TUNE; the radio sends a low-power tuning carrier and matches the antenna to ~1.2:1 SWR.
使用射频/中频增益和音频增益分开控制的通信接收机进行收听时，可以这样设置：
- A信号特弱时尽量把射频/中频增益开到最大，信号特强时尽量把音频增益开到最大，然后从低到高调整另一个增益以得到适当的音量
- B信号特弱时尽量把音频增益开到最大，信号特强时尽量把射频/中频增益开到最大，然后从低到高调整另一个增益以得到适当的音量
- C任何情况下都应将射频/中频增益放在中间位置，然后从低到高调整音频增益以得到适当的音量
- D任何情况下都应将音频增益放在中间位置，然后从低到高调整射频/中频增益以得到适当的音量
When listening with a communications receiver that has separate RF/IF gain and audio gain controls, you can set it like this:
- Awhen the signal is extremely weak, turn the RF/IF gain to maximum; when the signal is extremely strong, turn the audio gain to maximum; then adjust the other gain from low to high to get an appropriate volume
- Bwhen the signal is extremely weak, turn the audio gain to maximum; when the signal is extremely strong, turn the RF/IF gain to maximum; then adjust the other gain from low to high to get an appropriate volume
- Cin all cases keep the RF/IF gain at the middle position, then adjust the audio gain from low to high to get an appropriate volume
- Din all cases keep the audio gain at the middle position, then adjust the RF/IF gain from low to high to get an appropriate volume
With separate RF/IF gain and audio gain, the best practice is: for a very weak signal maximize RF/IF gain (to keep the best SNR before the noise floor) and use audio gain only for comfort; for a very strong signal you can max audio gain but must reduce RF/IF gain (or use ATT) to avoid front-end overload, then set the other control for volume. Option A captures this. B reverses the weak-signal rule (max audio on weak signal just raises hiss); C/D’s fixed-middle rules ignore the weak/strong distinction.
US–China difference: Same gain-staging principle taught for US communications receivers with separate RF and AF gain.
Common pitfall: Cranking audio gain for a weak signal — you only amplify noise, not the signal; raise RF/IF gain first for best SNR.
Real on-air practice: Weak 40 m CW → RF gain full, AF gain moderate; strong broadcaster → RF gain down, AF up, to keep the front end from blocking.
HF通信与VHF或UHF通信相比，最大的不同是什么？
- AHF通信依靠电离层的反射
- BHF传播更为稳定，衰落小
- CHF天线体积小
- DHF更适合远距离宽带通信
Compared with VHF or UHF communication, what is the biggest difference of HF communication?
- AHF communication relies on reflection from the ionosphere
- BHF propagation is more stable, with less fading
- CHF antennas are small in size
- DHF is more suitable for long-distance broadband communication
The defining feature of HF (short wave, 3–30 MHz) is skywave propagation — signals refract off the ionosphere (电离层) and return to Earth, enabling intercontinental communication. VHF/UHF are essentially line-of-sight. Option A is correct. B is false (HF fading is often severe); C is false (HF antennas are larger, e.g. 40 m dipole ≈ 20 m); D is false (HF channels are narrow, not broadband).
US–China difference: Same HF-skywave vs VHF/UHF-line-of-sight distinction taught in US license exams (Technician/General/Extra).
Common pitfall: Thinking HF is more stable than VHF. HF is actually prone to fading and depends on ionospheric conditions (day/night, solar cycle).
Real on-air practice: A 20 m (14 MHz) contact reaches Europe from China via the ionosphere, while your 145 MHz FM only reaches the local repeater line-of-sight.
下面哪种方法可以减小话筒或耳机用音频电缆可能感生的射频电流？
- A在电缆外面穿套铁氧体磁环
- B在电缆芯线中串联低通滤波器
- C在电缆前端添置话筒放大器
- D在电缆芯线中串联带通滤波器
Which of the following methods can reduce the RF current that may be induced in the audio cable of a microphone or headphones?
- Athread a ferrite ring over the outside of the cable
- Bseries-connect a low-pass filter in the cable’s core wire
- Cadd a microphone amplifier at the front of the cable
- Dseries-connect a band-pass filter in the cable’s core wire
RF current induced on an audio lead is best suppressed by a ferrite choke (铁氧体磁环) slipped over the cable — it adds common-mode impedance at RF without affecting the audio. Option A is correct. Putting filters in the core wire (B/D) would distort the audio; a mic amp (C) does nothing for RFI.
US–China difference: Same ferrite-bead/choke remedy used worldwide for RF in the shack (a US favorite fix for “RF in the mic”/hot-mic).
Common pitfall: Adding filters in the signal path — that degrades audio. The ferrite goes around the outside of the whole cable as a common-mode choke.
Real on-air practice: You clip a ferrite ring onto the mic cable and the “RF feedback in your voice / hot mic” on 20 m disappears.
业余中继台上下行共用一副天线时，需要在接收机、发信机和天线之间插入一个：
- A双工器（duplexer）
- B收发信转换开关
- C功率分配器（power divider）
- D环形器（circulator）
When an amateur repeater shares one antenna for uplink and downlink, a ___ must be inserted between the receiver, transmitter, and antenna:
- Aduplexer
- Btransmit-receive (T/R) switch
- Cpower divider
- Dcirculator
A repeater using one antenna for both receive (uplink) and transmit (downlink) needs a duplexer — a pair of filters that let the receiver and transmitter share the same antenna while isolating them (A). A T/R switch is for half-duplex single-station use, a power divider splits power, and a circulator is directional but not the standard shared-antenna solution described.
US–China difference: US repeaters use the same duplexer concept; the term is identical.
Common pitfall: Confusing the duplexer (simultaneous Tx/Rx sharing one antenna) with a simple T/R switch (alternating).
Real on-air practice: A 2 m repeater with a single antenna on a tower uses a duplexer to keep its own transmitter out of its receiver.
业余中继台上下行共用一副天线时，需要在接收机、发射机与天线之间插入一个双工器。其基本构造和作用为：
- A一组滤波器；阻止中继台发射的信号反馈进入中继台的接收机
- B一组半导体开关；在中继台发射时关断中继台的接收机
- C一个匹配网络；使天线、中继发射机、中继接收机三者之间都满足阻抗匹配关系
- D一个环形器；使信号只能沿中继发射机-天线-中继接收机的方向行进
When an amateur repeater shares one antenna for uplink and downlink, a duplexer is inserted between the receiver, transmitter, and antenna. Its basic construction and function are:
- Aa set of filters; it prevents the repeater’s transmitted signal from feeding back into the repeater’s receiver
- Ba set of semiconductor switches; it cuts off the repeater’s receiver while the repeater transmits
- Ca matching network; it makes the antenna, repeater transmitter, and repeater receiver all satisfy impedance matching
- Da circulator; it makes signals travel only along the path repeater transmitter → antenna → repeater receiver
A duplexer is essentially a set of cavity/coaxial filters: one passes the transmit frequency to the antenna while rejecting it from the receiver, and the other does the reverse, so the strong transmitted signal cannot overload or feed back into the receiver (A). It is not a switch (B), a mere matching network (C), or a one-way circulator path (D).
US–China difference: Identical duplexer principle in US repeaters.
Common pitfall: Thinking a duplexer is just an impedance-matching device; its key job is frequency-selective isolation.
Real on-air practice: Without a properly tuned duplexer, a repeater’s own transmitter would desense (block) its receiver.
在架设业余中继台之前必须调查台址附近有没有其他频率的发射机，其信号强到可以在中继台的接收机中与中继台的下行信号产生三阶互调，并且互调产物落入中继台的上行频率范围内。如果中继台的上、下行频率分别为fR和fT，则可能造成这种三阶互调干扰的频率fX可以计算为：
- A2fT – fR或 (fT + fR ) / 2
- BfT – fR或fT + fR
- C2（fT – fR）或2(fT + fR )
- D2fT或2fR
Before erecting an amateur repeater you must check whether there are nearby transmitters on other frequencies whose signals are strong enough to produce third-order intermodulation with the repeater’s downlink signal inside the repeater’s receiver, with the intermod product falling within the repeater’s uplink frequency range. If the repeater’s uplink and downlink frequencies are fR and fT respectively, the frequency fX that may cause such third-order intermodulation interference can be calculated as:
- A2fT − fR, or (fT + fR) / 2
- BfT − fR, or fT + fR
- C2(fT − fR), or 2(fT + fR)
- D2fT, or 2fR
Third-order intermodulation products take the form 2F₁ − F₂ or F₁ + F₂ − F₃. Here the repeater’s own downlink fT and an external signal fX mix to produce the uplink fR: 2fT − fX = fR ⇒ fX = 2fT − fR; and 2fX − fT = fR ⇒ fX = (fT + fR)/2. Both are the standard formulas, so A is correct.
US–China difference: Same intermod math applies to US repeater coordination; US coordinators also survey for “hostile” frequencies.
Common pitfall: Forgetting the 2fT − fR form and only recalling the average (fT+fR)/2.
Real on-air practice: A coordinator computes these “IM products” and tells you which nearby commercial transmitters could kill your repeater.
某业余中继台的发射机常被断断续续的干扰信号激发，其中夹杂模糊不清的话音。根据覆盖区域内其他业余电台守听，出现问题时上行频率上并无其他电台在工作。则：
- A这可能是中继台附近另外两部发射机的强信号在中继台的接收机中产生了等同于上行频率的互调干扰，打开了静噪
- B这肯定是中继台接收机受到了人为恶意干扰
- C这可能是中继台接收机发生了寄生振荡
- D这可能是中继台发射机发生了寄生振荡
A certain amateur repeater’s transmitter is often triggered by intermittent interference signals, mixed with indistinct voice. According to monitoring by other amateur stations in coverage, no other station is operating on the uplink frequency when the problem occurs. Then:
- AThis may be intermodulation interference produced in the repeater’s receiver by strong signals from two other nearby transmitters, generating a signal equal to the uplink frequency that opens the squelch.
- BThis definitely means the repeater’s receiver is under deliberate malicious interference.
- CThis may be parasitic oscillation occurring in the repeater’s receiver.
- DThis may be parasitic oscillation occurring in the repeater’s transmitter.
Because no station is actually on the uplink yet the repeater keys up with voice-like noise, the likely cause is third-order intermodulation: two strong off-frequency signals mix in the repeater receiver to produce a product exactly on the uplink frequency, opening the squelch (A). “Definitely malicious” (B) is too strong; parasitic oscillation (C, D) would not mimic voice from external signals.
US–China difference: US repeaters suffer the same intermod from nearby pagers/commercial transmitters; coordination minimizes it.
Common pitfall: Jumping to “jamming” before checking for intermod from legitimate strong signals.
Real on-air practice: A repeater near a broadcast tower may key up from intermod; the fix is better filtering/isolation, not accusing anyone.
某FM业余中继台的发射机一旦被上行信号启动就会持续发射，即使上行信号消失也不停止。可能的原因是：
- A中继台上下行隔离不良，中继台自身发射的信号窜入了中继台的接收机，造成自锁
- B肯定受到了人为恶意干扰
- C中继台接收机电源电压不稳
- D中继台发射机电源电压不稳
Once an FM amateur repeater’s transmitter is started by an uplink signal, it keeps transmitting even after the uplink signal disappears. The possible cause is:
- Apoor uplink/downlink isolation at the repeater, causing the repeater’s own transmitted signal to leak into its receiver, creating self-locking.
- Bit is definitely under deliberate malicious interference.
- Cunstable supply voltage to the repeater’s receiver.
- Dunstable supply voltage to the repeater’s transmitter.
If the repeater’s own downlink leaks back into its receiver (poor isolation between uplink and downlink), the receiver keeps seeing a “signal” and holds the transmitter on — a self-locking loop (A). This is a technical fault, not necessarily jamming (B), and power-supply issues (C, D) wouldn’t cause a sustained key-up tied to the uplink path.
US–China difference: US repeater builders also must ensure adequate Tx/Rx isolation to avoid “self-lock”.
Common pitfall: Assuming malicious jamming before checking duplexer isolation and feed-line loss.
Real on-air practice: A repeater that won’t unkey usually needs duplexer retuning or more antenna isolation.
FM业余中继台的发射机可以被上行信号正常启动。但是在上行信号消失后，该台常会继续发射一段时间，或长或短，其中夹杂模糊不清的语音。可能的原因是：
- A中继台的下行信号与附近其他发射机的信号在中继台接收机中产生了等同于上行频率的互调干扰
- B肯定是受到了人为恶意干扰
- C中继台接收机电源电压不稳
- D中继台发射机电源电压不稳
An FM amateur repeater’s transmitter can be normally started by an uplink signal. But after the uplink signal disappears, the station often continues transmitting for a while, with indistinct voice embedded. The possible cause is:
- AThe repeater’s downlink signal and signals from other nearby transmitters produce intermodulation interference equal to the uplink frequency in the repeater’s receiver.
- BIt is definitely under deliberate malicious interference.
- Cunstable supply voltage to the repeater’s receiver.
- Dunstable supply voltage to the repeater’s transmitter.
After the legitimate uplink stops, if the repeater keeps transmitting with voice-like noise, an external signal mixing with the repeater’s own downlink can generate an intermod product on the uplink frequency that re-opens the squelch (A). As in U0842, this is intermod, not necessarily jamming (B) or power issues (C, D).
US–China difference: Same failure mode seen in US repeaters near strong commercial sites.
Common pitfall: Immediately blaming jamming rather than characterizing the intermod source.
Real on-air practice: Identifying the two offending transmitters and adding filtering resolves the “stuck carrier”.
💬 Have questions about this topic, or FCC / CRAC exam preparation?
对本篇内容或 FCC / CRAC 备考有疑问？
本手册仅供业余无线电爱好者学习交流，题库原题版权归 CRAC（中国无线电协会业余无线电分会）所有，英文翻译由 BG7BAG 编译，转载请注明出处。
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