CRAC Bilingual Manual › Part: Electrical Basics for Amateur Radio
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 Transistor Amplifier Circuits with 106 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.
图中的电路为：
- A共基极放大器
- B共发射极放大器
- C共集电极放大器
- D共栅极放大器 [F]LK0734.jpg
The circuit shown in the figure is:
- Aa common-base amplifier
- Ba common-emitter amplifier
- Ca common-collector amplifier
- Da common-gate amplifier (see figure LK0734.jpg)
The figure (LK0734.jpg) shows the input applied to the emitter and the output taken from the collector with the base AC-grounded (biasing network) — i.e. the 共基极放大器 (common-base amplifier), where the base is the common terminal. A is correct; common-gate is the FET counterpart in D.
US–China difference: Same three BJT configurations (common-base/emitter/collector) in US courses.
Common pitfall: Confusing common-base with common-emitter by misidentifying the grounded/AC-grounded terminal.
Real on-air practice: Common-base stages are used in VHF amplifiers for their good high-frequency response.
在下面的三极管放大电路中，Rc的常用名称和作用是：
- A负载电阻；将集电极电流转换为输出的信号电压
- B发射极负反馈电阻；稳定直流工作点
- C偏流电阻；为晶体管提供偏置电流以使电路获得适当的工作点
- D集电极负反馈电阻；提供负反馈，减少信号失真 [F]LK0740.jpg
In the transistor amplifier circuit below, the common name and function of Rc is:
- Aload resistor; it converts the collector current into the output signal voltage
- Bemitter negative-feedback resistor; stabilizes the DC operating point
- Cbias resistor; provides bias current so the circuit obtains a proper operating point
- Dcollector negative-feedback resistor; provides negative feedback to reduce signal distortion (see figure LK0740.jpg)
In a common-emitter stage, Rc (collector resistor) is the 负载电阻 (load resistor): the varying collector current develops the output signal voltage across it (Vout = Vcc − Ic·Rc). A is correct; Re is the emitter feedback resistor, Rb the bias resistor.
US–China difference: Same Rc/Re/Rb roles in US amplifier schematics.
Common pitfall: Calling Rc a feedback or bias resistor — it is the collector load.
Real on-air practice: Choosing Rc sets your stage gain and collector voltage swing.
在下面的三极管放大电路中，Re的常用名称和作用是：
- A发射极负反馈电阻；稳定直流工作点
- B负载电阻；将集电极电流转换为输出的信号电压
- C集电极负反馈电阻；提供负反馈，减少信号失真
- D偏流电阻；为晶体管提供偏置电流以使电路获得适当的工作点 [F]LK0741.jpg
In the transistor amplifier circuit below, the common name and function of Re is:
- Aemitter negative-feedback resistor; stabilizes the DC operating point
- Bload resistor; converts the collector current into the output signal voltage
- Ccollector negative-feedback resistor; provides negative feedback to reduce signal distortion
- Dbias resistor; provides bias current so the circuit obtains a proper operating point (see figure LK0741.jpg)
Re is the 发射极负反馈电阻 (emitter resistor); the DC voltage drop across it provides negative feedback that stabilizes the operating (quiescent) point against temperature/β variations. A is correct; Rb is the bias resistor.
US–China difference: Same emitter degeneration role in US designs.
Common pitfall: Confusing Re (emitter, stabilization) with Rb (base bias).
Real on-air practice: A small unbypassed Re linearizes your audio stage and sets gain.
在下面的三极管放大电路中，Rb1的常用名称和作用是：
- A偏流电阻；为晶体管提供偏置电流以使电路获得适当的工作点
- B负载电阻；将集电极电流转换为输出的信号电压
- C发射极负反馈电阻；稳定直流工作点
- D基极负反馈电阻；提供负反馈，减少信号失真 [F]LK0742.jpg
In the transistor amplifier circuit below, the common name and function of Rb1 is:
- Abias resistor; provides bias current to the transistor so the circuit obtains a proper operating point
- Bload resistor; converts the collector current into the output signal voltage
- Cemitter negative-feedback resistor; stabilizes the DC operating point
- Dbase negative-feedback resistor; provides negative feedback to reduce signal distortion (see figure LK0742.jpg)
Rb1 is the upper 偏流电阻 (bias resistor) of the base divider; it sets the base bias current/voltage that establishes the operating point. A is correct; Rc is the load and Re is the emitter feedback.
US–China difference: Same base-bias divider (Rb1/Rb2) in US textbooks.
Common pitfall: Calling a bias resistor a feedback resistor.
Real on-air practice: Pick Rb1/Rb2 to sit your Q-point mid-supply for maximum swing.
在下面的三极管放大电路中，Cb的常用名称和作用是：
- A输入耦合（或隔直流）电容；使输入交流信号进入放大器但隔断直流分量
- B输出耦合（或隔直流）电容；使输出交流信号顺利输出但隔断直流分量
- C旁路电容；使发射极交流信号顺利通过，避免在Re造成压降，形成负反馈
- D负反馈电容；提供负反馈，减少信号失真 [F]LK0743.jpg
In the transistor amplifier circuit below, the common name and function of Cb is:
- Ainput coupling (or DC-blocking) capacitor; lets the input AC signal enter the amplifier but blocks the DC component
- Boutput coupling (or DC-blocking) capacitor; lets the output AC signal pass but blocks DC
- Cbypass capacitor; lets the emitter AC signal pass freely, avoiding a voltage drop across Re that would form negative feedback
- Dnegative-feedback capacitor; provides negative feedback to reduce signal distortion (see figure LK0743.jpg)
Cb at the input is the 输入耦合电容 (input coupling/DC-blocking capacitor): it passes the AC signal into the base while blocking DC bias from the preceding stage. A is correct; Cc is the output coupler and Ce the emitter bypass.
US–China difference: Same coupling-cap function in US circuits.
Common pitfall: Mixing up Cb (input), Cc (output), and Ce (bypass).
Real on-air practice: A mic’s coupling cap keeps your bias off the microphone while passing audio.
在下面的三极管放大电路中，Ce的常用名称和作用是：
- A旁路电容；使发射极交流信号顺利通过，避免在Re造成压降，形成负反馈
- B输入耦合（或隔直流）电容；使输入交流信号进入放大器但隔断直流分量
- C输出耦合（或隔直流）电容；使输出交流信号顺利输出但隔断直流分量
- D负反馈电容；提供负反馈，减少信号失真 [F]LK0744.jpg
In the transistor amplifier circuit below, the common name and function of Ce is:
- Abypass capacitor; lets the emitter AC signal pass freely, avoiding a voltage drop across Re that would form negative feedback
- Binput coupling (or DC-blocking) capacitor; lets the input AC signal enter the amplifier but blocks DC
- Coutput coupling (or DC-blocking) capacitor; lets the output AC signal pass but blocks DC
- Dnegative-feedback capacitor; provides negative feedback to reduce signal distortion (see figure LK0744.jpg)
Ce is the 旁路电容 (emitter bypass capacitor) across Re: at AC it shorts the emitter to ground so Re does not degenerate (reduce) the gain, while DC still sees Re for bias stability. A is correct.
US–China difference: Same emitter-bypass role in US designs.
Common pitfall: Thinking Ce blocks DC — it bypasses AC; Re still sets DC bias.
Real on-air practice: A poorly chosen Ce lowers low-frequency gain (poor bass response).
在下面的三极管放大电路中，Cc的常用名称和作用是：
- A输出耦合（或隔直流）电容；使输出交流信号顺利输出但隔断直流分量
- B输入耦合（或隔直流）电容；使输入交流信号进入放大器但隔断直流分量
- C旁路电容；使发射极交流信号顺利通过，避免在Re造成压降，形成负反馈
- D负反馈电容；提供负反馈，减少信号失真 [F]LK0745.jpg
In the transistor amplifier circuit below, the common name and function of Cc is:
- Aoutput coupling (or DC-blocking) capacitor; lets the output AC signal pass freely while blocking the DC component
- Binput coupling (or DC-blocking) capacitor; lets the input AC signal enter the amplifier but blocks DC
- Cbypass capacitor; lets the emitter AC signal pass freely, avoiding a voltage drop across Re that would form negative feedback
- Dnegative-feedback capacitor; provides negative feedback to reduce signal distortion (see figure LK0745.jpg)
Cc at the output is the 输出耦合电容 (output coupling/DC-blocking capacitor): it transmits the amplified AC to the next stage while blocking the collector’s DC bias. A is correct; Cb is the input coupler.
US–China difference: Same output-coupling function in US schematics.
Common pitfall: Swapping Cc (output) with Cb (input).
Real on-air practice: Your output cap keeps the antenna system isolated from the DC collector voltage.
下列电路具备的功能是：
- A低通滤波
- B带通滤波
- C高通滤波
- D过流保护 [F]LK0594.jpg
The function of the following circuit is:
- Alow-pass filtering
- Bband-pass filtering
- Chigh-pass filtering
- Dovercurrent protection (see figure LK0594.jpg)
The figure (LK0594.jpg) shows a shunt capacitor to ground at the output of a series resistor (or L-section R-C), which passes low frequencies and attenuates high frequencies — a 低通滤波 (low-pass filter). A is correct; it is not a band-pass, high-pass, or protection element.
US–China difference: Same R-C low-pass topology in US material.
Common pitfall: Identifying the cutoff direction wrongly (low-pass vs high-pass) from capacitor placement.
Real on-air practice: A low-pass feedline filter keeps your HF harmonics out of VHF receivers.
下列电路是一个：
- A电感耦合式振荡器
- B电容三点式振荡器
- C电感三点式振荡器
- DRC反馈式振荡器 [F]LK0605.jpg
The following circuit is a:
- Ainductively-coupled oscillator
- BColpitts oscillator (capacitive tapped)
- CHartley oscillator (inductive tapped)
- DRC-feedback oscillator (see figure LK0605.jpg)
The figure (LK0605.jpg) depicts an oscillator whose feedback is taken via a coupling/transformer winding (inductive coupling) between the tuned collector circuit and the base — an 电感耦合式振荡器 (inductively-coupled oscillator). A is correct; Colpitts/Hartley use a tapped capacitor/inductor divider and RC-feedback uses resistors/caps.
US–China difference: Same oscillator families (Hartley, Colpitts, transformer-feedback) in US courses.
Common pitfall: Confusing transformer-coupled feedback with the tapped (Hartley/Colpitts) types.
Real on-air practice: Many vintage CW VFOs use a transformer-coupled oscillator stage.
金属氧化物绝缘栅场效应管（MOSFET）经常用来实现只有开与关两个状态的电路。在这种电路中，术语“截止”与”饱和”是指晶体管的什么工作状态？
- A所加偏压不足以使该管导通，则该管处于截止状态；所加偏压使该管充分导通，继续强化偏压而导通电阻几乎不再减小的状态为饱和状态
- B所加偏压不足以使该管导通，则该管处于截止状态；所加偏压使该管开始导通，继续强化偏压则导通电阻随之逐渐减小的状态为饱和状态
- C加上偏压使该管导通，则该管进入饱和状态；将偏压归零，则该管处于截止状态
- D偏压快速变化，以至于该管导通时的损耗大增就是所谓的饱和；反之即是截止了
A metal-oxide semiconductor field-effect transistor (MOSFET) is often used in circuits that have only two states, on and off. In such a circuit, what operating states do the terms “cutoff” and “saturation” refer to?
- Aif the applied bias is insufficient to turn the device on, it is in cutoff; when the bias fully turns it on and further increasing the bias barely reduces the on-resistance, that state is saturation
- Bif the bias is insufficient to turn it on, it is in cutoff; when the bias just begins to turn it on and further bias gradually reduces the on-resistance, that state is saturation
- Capplying bias to turn it on means it enters saturation; returning bias to zero means it is in cutoff
- Drapid bias change causing a large rise in conduction loss is “saturation”; the opposite is cutoff
For a MOSFET switch, 截止 (cutoff) = bias too low to conduct (off); 饱和 (saturation, as a switch) = fully enhanced so the channel is as low-resistance as it gets and extra gate voltage barely lowers Rds(on) (on). A correctly defines both; B wrongly says resistance keeps dropping (that is the linear/triode region, not saturation); C/D are imprecise.
US–China difference: Same MOSFET cutoff/saturation (switch) definitions in US courses — note “saturation” means opposite for BJTs.
Common pitfall: Confusing MOSFET saturation (fully on) with BJT saturation, or with the linear region.
Real on-air practice: Your PA’s MOSFET final is driven between cutoff and saturation for efficient switching (Class E/D).
关于场效应晶体管放大器的放大作用，以下说法正确的是：
- A共源极形式：栅极电压的微小变化可以引起漏极电压和电流的较大变化
- B共栅极形式：源极电流的微小变化可以引起漏极电压的较大变化
- C共漏极形式：栅极电压的微小变化可以引起源极电流的较大变化
- D无论哪种电路形式，放大器均在输入信号足够大时自动转变为功率放大器
Regarding the amplification of a field-effect transistor amplifier, which of the following statements is correct? (Choose all that apply.)
- Acommon-source form: a small change in gate voltage causes a large change in drain voltage and current
- Bcommon-gate form: a small change in source current causes a large change in drain voltage
- Ccommon-drain form: a small change in gate voltage causes a large change in source current
- Dregardless of configuration, the amplifier automatically becomes a power amplifier when the input is large enough
Each FET configuration provides voltage/current gain: common-source (栅极→漏极) gives large drain voltage/current change from small gate change (A); common-gate (源极→漏极) gives drain-voltage change from source-current change (B); common-drain/source-follower (栅极→源极) gives source-current change from gate change (C). D is false — a small-signal amplifier does not “become” a PA at large drive; it clips.
US–China difference: Same FET configurations (CS/CG/CD) in US material.
Common pitfall: Believing large drive turns any amplifier into a power amplifier — it causes distortion.
Real on-air practice: A common-source JFET is the gain stage in many receive preamps.
关于双极型晶体管放大器的放大作用，以下说法正确的是：
- A共发射极形式：基极电流的微小变化可以引起集电极电压和电流的较大变化
- B共基极形式：发射极电流的微小变化可以引起集电极电压的较大变化
- C共集电极形式：基极电流的微小变化可以引起发射极电流的较大变化
- D无论哪种电路形式，放大器均在输入信号足够大时自动转变为功率放大器
Regarding the amplification of a bipolar-junction transistor amplifier, which of the following statements is correct? (Choose all that apply.)
- Acommon-emitter form: a small change in base current causes a large change in collector voltage and current
- Bcommon-base form: a small change in emitter current causes a large change in collector voltage
- Ccommon-collector form: a small change in base current causes a large change in emitter current
- Dregardless of configuration, the amplifier automatically becomes a power amplifier when the input is large enough
Bipolar transistor gain by configuration: common-emitter (基极→集电极) gives large collector voltage/current swing from small base current (A); common-base (发射极→集电极) gives collector-voltage change from emitter current (B); common-collector/emitter-follower (基极→发射极) gives large emitter-current change from base current (C). D is false for the same reason as the FET case — large drive causes clipping, not automatic PA operation.
US–China difference: Same BJT configurations (CE/CB/CC) in US courses.
Common pitfall: Thinking overdriving converts a stage into a PA.
Real on-air practice: Common-emitter driver stages give most of your receiver IF gain.
对于双极型晶体管放大器，按输入阻抗由低到高可以排列为：
- A共基极放大器、共发射极放大器、共集电极放大器
- B共发射极放大器、共集电极放大器、共基极放大器
- C共集电极放大器、共发射极放大器、共基极放大器
- D共集电极放大器、共基极放大器、共发射极放大器
For bipolar-junction transistor amplifiers, ordered from lowest to highest input impedance:
- Acommon-base amplifier, common-emitter amplifier, common-collector amplifier
- Bcommon-emitter amplifier, common-collector amplifier, common-base amplifier
- Ccommon-collector amplifier, common-emitter amplifier, common-base amplifier
- Dcommon-collector amplifier, common-base amplifier, common-emitter amplifier
Input impedance: common-base is lowest (≈re), common-emitter is medium (≈β·re), common-collector (emitter follower) is highest (≈β·(re+RE’)). So lowest→highest is CB, CE, CC. A is correct.
US–China difference: Same impedance ordering in US courses.
Common pitfall: Placing common-collector (highest Zin) at the low end.
Real on-air practice: An emitter follower buffers a high-impedance source to a low-Z load.
对于双极型晶体管放大器，按电流增益由低到高可以排列为：
- A共基极放大器、共发射极放大器、共集电极放大器
- B共集电极放大器、共发射极放大器、共基极放大器
- C共发射极放大器、共集电极放大器、共基极放大器
- D共集电极放大器、共基极放大器、共发射极放大器
For bipolar-junction transistor amplifiers, ordered from lowest to highest current gain:
- Acommon-base amplifier, common-emitter amplifier, common-collector amplifier
- Bcommon-collector amplifier, common-emitter amplifier, common-base amplifier
- Ccommon-emitter amplifier, common-collector amplifier, common-base amplifier
- Dcommon-collector amplifier, common-base amplifier, common-emitter amplifier
Current gain: common-base ≈ α (<1, no current gain); common-emitter ≈ β (tens to hundreds); common-collector ≈ β+1 (≈β, the largest). So lowest→highest is CB, CE, CC. A is correct.
US–China difference: Same α/β/β+1 ordering in US material.
Common pitfall: Forgetting common-base has current gain < 1.
Real on-air practice: Common-base buffers RF without current gain but with good bandwidth.
对于双极型晶体管放大器，电压增益由低到高可以排列为：
- A共集电极放大器、共基极放大器、共发射极放大器
- B共基极放大器、共发射极放大器、共集电极放大器
- C共集电极放大器、共发射极放大器、共基极放大器
- D共发射极放大器、共集电极放大器、共基极放大器
For bipolar-junction transistor amplifiers, ordered from lowest to highest voltage gain:
- Acommon-collector amplifier, common-base amplifier, common-emitter amplifier
- Bcommon-base amplifier, common-emitter amplifier, common-collector amplifier
- Ccommon-collector amplifier, common-emitter amplifier, common-base amplifier
- Dcommon-emitter amplifier, common-collector amplifier, common-base amplifier
Voltage gain: common-collector (emitter follower) ≈ 1 (lowest); common-base is moderate (≈gm·Rc); common-emitter is highest (≈gm·Rc with full gain, no local degeneration). So lowest→highest is CC, CB, CE. A is correct.
US–China difference: Same voltage-gain ordering in US courses.
Common pitfall: Putting the emitter follower (≈1) at the top.
Real on-air practice: Common-emitter stages supply most IF/RF voltage gain; followers give none.
对于双极型晶体管放大器，输出阻抗由低到高可以排列为：
- A共集电极放大器、共发射极放大器、共基极放大器
- B共集电极放大器、共基极放大器、共发射极放大器
- C共基极放大器、共发射极放大器、共集电极放大器
- D共发射极放大器、共集电极放大器、共基极放大器
For bipolar-junction transistor amplifiers, ordered from lowest to highest output impedance:
- Acommon-collector amplifier, common-emitter amplifier, common-base amplifier
- Bcommon-collector amplifier, common-base amplifier, common-emitter amplifier
- Ccommon-base amplifier, common-emitter amplifier, common-collector amplifier
- Dcommon-emitter amplifier, common-collector amplifier, common-base amplifier
Output impedance: common-collector (emitter follower) is lowest (≈re+source/β); common-emitter is medium; common-base is highest (≈ro·… large). So lowest→highest is CC, CE, CB. A is correct.
US–China difference: Same output-impedance ordering in US material.
Common pitfall: Reversing CE and CB output impedance.
Real on-air practice: A low-Z emitter follower drives a 50 Ω line well.
在双极型晶体管放大电路中，常被称为射极跟随器的是：
- A共集电极放大电路
- B共发射极放大电路
- C共基极放大电路
- D带有正反馈的共发射极放大电路
In a bipolar-junction transistor amplifier circuit, the configuration commonly called an emitter follower is:
- Athe common-collector amplifier circuit
- Bthe common-emitter amplifier circuit
- Cthe common-base amplifier circuit
- Da common-emitter amplifier circuit with positive feedback
The 射极跟随器 (emitter follower) is the 共集电极放大电路 (common-collector amplifier): the output is taken from the emitter, which “follows” the base voltage. A is correct; it has unity voltage gain and is used for buffering/impedance matching.
US–China difference: Same “emitter follower = common-collector” term in US courses.
Common pitfall: Confusing it with common-emitter (the gain stage).
Real on-air practice: You use an emitter follower to drive a low-impedance antenna relay line.
关于电子三极管放大器的放大作用，以下说法正确的是：
- A共阴极形式：栅极电压的微小变化可以引起屏极电压和电流的较大变化
- B共栅极形式：阴极电流的微小变化可以引起屏极电压的较大变化
- C共屏极形式：栅极电压的微小变化可以引起阴极电流的较大变化
- D无论哪种电路形式，放大器均在输入信号足够大时自动转变为功率放大器
Which of the following statements about the amplification of a triode (electron-tube) amplifier is correct? (Choose all that apply.)
- ACommon-cathode configuration: a small change in grid voltage can cause a large change in plate voltage and current
- BCommon-grid configuration: a small change in cathode current can cause a large change in plate voltage
- CCommon-plate configuration: a small change in grid voltage can cause a large change in cathode current
- DRegardless of circuit configuration, the amplifier automatically becomes a power amplifier when the input signal is large enough
A triode amplifier provides gain in any of its three basic configurations. In the common-cathode (共阴极) stage the small-signal grid voltage controls both plate current and plate voltage (A). In the common-grid (共栅极) stage the grounded grid blocks grid–plate capacitance while the cathode input current change is reflected as a plate-voltage change (B). In the common-plate or cathode-follower (共屏极) stage a grid-voltage change drives a corresponding cathode-current change (C). All three describe valid amplification mechanisms. D is false: a voltage amplifier does not “automatically” become a power amplifier merely because the input grows — power amplification depends on the stage’s design and load, not input level.
US–China difference: US hams study the same three tube configurations (common-cathode, common-grid, common-plate/cathode-follower) in amplifier design.
Common pitfall: Mixing up which electrode is grounded in each configuration, or assuming big input turns any stage into a PA.
Real on-air practice: A cathode-follower (common-plate) gives low output impedance to drive coax after a high-impedance driver stage.
小信号放大器是指：
- A工作点始终处于线性工作区的放大器
- B输出信号的峰-峰值始终小于10伏的放大器
- C输入信号的峰-峰值始终小于10毫伏的放大器
- D增益不超过30dB的放大器
A small-signal amplifier is:
- Aan amplifier whose operating point always stays within the linear operating region
- Ban amplifier whose output signal peak-to-peak value is always below 10 volts
- Can amplifier whose input signal peak-to-peak value is always below 10 millivolts
- Dan amplifier whose gain does not exceed 30 dB
A 小信号放大器 (small-signal amplifier) is defined by its operating condition: the operating point (Q-point) remains in the linear region at all times, so the active device behaves linearly. B, C, and D try to define it by arbitrary voltage or gain thresholds, which is incorrect — the defining feature is the linear operating point, not a fixed voltage or gain number.
US–China difference: Same definition in the US: small-signal means operation about a fixed Q-point within the linear region.
Common pitfall: Trying to pin “small-signal” to a specific peak-to-peak voltage or gain figure.
Real on-air practice: The receive IF and audio pre-amp stages in your rig are small-signal stages preceding the power amplifier.
大信号放大器是指：
- A工作点可以超出线性工作区的放大器
- B输出信号的峰-峰值大于10伏的放大器
- C输入信号的峰-峰值大于10毫伏的放大器
- D增益超过30dB的放大器
A large-signal amplifier is:
- Aan amplifier whose operating point can go beyond the linear operating region
- Ban amplifier whose output signal peak-to-peak value is greater than 10 volts
- Can amplifier whose input signal peak-to-peak value is greater than 10 millivolts
- Dan amplifier whose gain exceeds 30 dB
A 大信号放大器 (large-signal amplifier, i.e. a power amplifier) is one whose operating point can swing outside the linear region, deliberately driving the device into cutoff/saturation or nonlinear operation to deliver power. B/C/D are arbitrary voltage or gain thresholds and do not define large-signal operation.
US–China difference: US “power amplifier” terminology matches: large-signal stages operate beyond the small-signal linear region.
Common pitfall: Defining large-signal by a fixed voltage or gain rather than by the operating-point excursion.
Real on-air practice: Your 100 W HF final is a large-signal stage; its devices swing well outside the linear region.
下列放大器中，电源效率最低的是：
- A甲类放大器
- B乙类放大器
- C丙类放大器
- D甲乙类放大器
Among the following amplifiers, the one with the lowest power-supply efficiency is:
- Athe Class A amplifier
- Bthe Class B amplifier
- Cthe Class C amplifier
- Dthe Class AB amplifier
电源效率 (plate/power-supply efficiency) is lowest for the 甲类放大器 (Class A amplifier), which conducts for the full 360° cycle and idles at a high quiescent current; its maximum theoretical efficiency is only about 25% (with a transformer) or 50% (inductor load). Class B/AB/C are progressively more efficient.
US–China difference: Same efficiency ranking in the US: Class A is the least efficient, Class C/D the most.
Common pitfall: Confusing distortion ranking with efficiency ranking — Class A is best for low distortion but worst for efficiency.
Real on-air practice: A Class-A driver stage runs hot because it wastes most DC power as heat.
下列放大器中，电源效率最高的是：
- A丙类放大器
- B甲类放大器
- C乙类放大器
- D甲乙类放大器
Among the following amplifiers, the one with the highest power-supply efficiency is:
- Athe Class C amplifier
- Bthe Class A amplifier
- Cthe Class B amplifier
- Dthe Class AB amplifier
Among conventional Classes A/B/AB/C, the 丙类放大器 (Class C amplifier) has the highest efficiency because its conduction angle is well under 180° and it idles at essentially zero current. (Class D switching amplifiers are even higher, but among the listed options Class C is the most efficient.)
US–China difference: Same: Class C is the highest-efficiency conventional linear-ish class used for constant-amplitude RF.
Common pitfall: Forgetting that high efficiency comes with high distortion, so Class C suits only constant-amplitude modes.
Real on-air practice: FM/CW finals often run Class C to keep the battery or PSU load low.
下列放大器中，波形失真最小的是：
- A甲类放大器
- B乙类放大器
- C丙类放大器
- D甲乙类放大器
Among the following amplifiers, the one with the smallest waveform distortion is:
- Athe Class A amplifier
- Bthe Class B amplifier
- Cthe Class C amplifier
- Dthe Class AB amplifier
The 甲类放大器 (Class A amplifier) conducts for the full 360° and the device never cuts off, so the output waveform tracks the input with the least distortion. Class B has crossover distortion, Class AB slightly less, and Class C is highly distorted without a tuned/linearizing network.
US–China difference: Identical principle in US amplifier theory.
Common pitfall: Pairing “least distortion” with a high-efficiency class — they are opposite trade-offs.
Real on-air practice: High-fidelity audio stages use Class A for clean sound.
下列放大器中，波形失真最大的是：
- A丙类放大器
- B甲类放大器
- C乙类放大器
- D甲乙类放大器
Among the following amplifiers, the one with the largest waveform distortion is:
- Athe Class C amplifier
- Bthe Class A amplifier
- Cthe Class B amplifier
- Dthe Class AB amplifier
The 丙类放大器 (Class C amplifier) has the largest waveform distortion because it conducts for less than half a cycle and clips the signal heavily; it only reproduces a clean waveform after a tuned (frequency-selective) network restores the fundamental. Class A is the least distorted, so A is the correct choice.
US–China difference: Same: Class C is the most distorted of the conduction-angle classes.
Common pitfall: Thinking Class D has the most distortion — among the listed A/B/AB/C, Class C is worst.
Real on-air practice: A Class-C stage feeding a tuned circuit emits a clean sine once the harmonics are filtered.
下列放大器中，适宜用作音频功率放大器的是：
- A甲乙类放大器
- B丙类放大器
- C甲类放大器
- D乙类放大器
Among the following amplifiers, the one suitable for use as an audio power amplifier is:
- Athe Class AB amplifier
- Bthe Class C amplifier
- Cthe Class A amplifier
- Dthe Class B amplifier
An audio power amplifier must reproduce the full waveform with low distortion yet deliver useful power. The 甲乙类放大器 (Class AB amplifier) is the standard choice: it has far less crossover distortion than pure Class B and much better efficiency than Class A, making it the practical audio PA. Class C cannot linearly amplify audio; pure Class B suffers crossover distortion; Class A is inefficient for power.
US–China difference: US audio power amps are almost universally Class AB (or Class D switching) for the same reasons.
Common pitfall: Picking pure Class B for audio — its crossover distortion is objectionable.
Real on-air practice: The speaker output stage of your transceiver is a Class AB push-pull amplifier.
下列放大器中，适宜用作音频小信号放大器的是：
- A甲类放大器
- B甲乙类放大器
- C丙类放大器
- D乙类放大器
Among the following amplifiers, the one suitable for use as an audio small-signal amplifier is:
- Athe Class A amplifier
- Bthe Class AB amplifier
- Cthe Class C amplifier
- Dthe Class B amplifier
An audio small-signal amplifier needs linearity and low distortion, with little concern for efficiency, so the 甲类放大器 (Class A amplifier) is the natural fit — it stays in the linear region and reproduces audio cleanly. Class C is unusable for audio; Class B/AB are power-stage choices, not small-signal pre-amp choices here.
US–China difference: US audio pre-amps commonly use Class A small-signal stages.
Common pitfall: Using a distortion-prone class for a low-level audio stage.
Real on-air practice: The AF gain stage before the speaker uses Class A for clean copy.
下列放大器中，适宜用作CW射频功率放大器的是：
- A接近乙类偏置的甲乙类放大器
- B接近甲类偏置的甲乙类放大器
- C丙类放大器
- D丁类放大器
Among the following amplifiers, those suitable for use as a CW RF power amplifier are: (Choose all that apply.)
- Aa Class AB amplifier biased close to Class B
- Ba Class AB amplifier biased close to Class A
- Cthe Class C amplifier
- Dthe Class D amplifier
CW is a constant-amplitude (on/off) emission, so both a near-Class-B-biased 甲乙类 (Class AB) stage (A) and a near-Class-A-biased Class AB stage (B) are suitable and commonly used. According to the official key, C (Class C) and D (Class D) are not selected here; note that in practical CW design Class C and switching Class D are also widely used for constant-amplitude keyed carriers, but the examination marks only A and B for this item.
US–China difference: US CW PAs likewise run Class AB or Class C; both countries treat CW as constant-amplitude.
Common pitfall: Assuming only one bias works for CW — Class AB near either extreme is fine.
Real on-air practice: Keying a near-Class-B AB stage gives clean CW with a shaped envelope.
下列放大器中，适宜用作FM射频功率放大器的是：
- A接近乙类的甲乙类放大器
- B接近甲类的甲乙类放大器
- C丙类放大器
- D甲类放大器
Among the following amplifiers, those suitable for use as an FM RF power amplifier are: (Choose all that apply.)
- Aa Class AB amplifier biased close to Class B
- Ba Class AB amplifier biased close to Class A
- Cthe Class C amplifier
- Dthe Class A amplifier
FM (frequency modulation) is a constant-amplitude mode, so the amplifier need not be linear in amplitude — any class that preserves the envelope works. A near-Class-B Class AB (A) and a near-Class-A Class AB (B) both give clean constant-amplitude output, and the 丙类放大器 (Class C amplifier) (C) is classically used for FM/CW PAs because its envelope stays constant. Class A (D) is inefficient and not the intended answer here.
US–China difference: US FM repeaters and HTs use Class C or AB finals for the same constant-envelope reason.
Common pitfall: Thinking FM needs a linear amplifier — it does not, since amplitude carries no information.
Real on-air practice: Your 2 m FM handheld final is a Class C stage; the envelope never varies.
下列放大器电路中，适宜用作SSB射频功率放大器的是：
- A接近乙类偏置的甲乙类放大器
- B接近甲类偏置的甲乙类放大器
- C丙类放大器
- D丁类放大器
Among the following amplifier circuits, those suitable for use as an SSB RF power amplifier are: (Choose all that apply.)
- Aa Class AB amplifier biased close to Class B
- Ba Class AB amplifier biased close to Class A
- Cthe Class C amplifier
- Dthe Class D amplifier
SSB (single sideband, 单边带 SSB) carries information in the envelope amplitude, so the PA must be linear to avoid distortion and splatter. A near-Class-B 甲乙类 (Class AB) stage (A) and a near-Class-A Class AB stage (B) are the standard linear SSB PAs. Class C (C) and Class D (D) are highly nonlinear and would destroy the SSB envelope, so they are incorrect.
US–China difference: US SSB线 amplifiers are linear Class AB (or Class A) for the same reason.
Common pitfall: Using a Class C final for SSB — it causes severe distortion and out-of-band splatter.
Real on-air practice: Your HF SSB final is a linear Class AB stage; over-driving it makes it nonlinear and dirty.
业余无线电爱好者常把放大器分为A、B、C、D等类别。在电路理论中，这些序号对应甲、乙、丙、丁四类放大器。放大器的分类与电路中有源器件在输入信号一个完整周期内的导通角度和导通程度有关，具体为：
- A对于A类放大器，器件在整个信号周期内导通，既不截止，也不饱和
- B对于B类放大器，器件恰好在半个信号周期内导通，但是永不饱和
- C对于C类放大器，器件的导通角度小于半个信号周期，并且器件在信号峰值时饱和工作
- D对于D类放大器，器件的导通角度至多半个信号周期，并且器件始终线性工作
Amateur radio operators often divide amplifiers into Classes A, B, C, D, etc., which in circuit theory correspond to Classes 甲, 乙, 丙, 丁. The classification relates to the conduction angle and degree of conduction of the active device over one full cycle of the input signal, specifically: (Choose all that apply.)
- AFor a Class A amplifier, the device conducts throughout the entire signal cycle, neither cutting off nor saturating
- BFor a Class B amplifier, the device conducts for exactly half a signal cycle, but never saturates
- CFor a Class C amplifier, the device’s conduction angle is less than half a signal cycle, and the device operates in saturation at the signal peaks
- DFor a Class D amplifier, the device’s conduction angle is at most half a signal cycle, and the device always operates linearly
Class A (甲类, A) conducts 360° and stays in the active region (no cutoff, no saturation). Class B (乙类, B) conducts 180° and does not saturate. Class C (丙类, C) conducts less than 180° and is driven into saturation at peaks. These three statements (A, B, C) are correct. D is wrong: 丁类 (Class D) is a switching amplifier — its devices are driven hard between cutoff and saturation (not linear), even though each may conduct ≤180°.
US–China difference: The A/B/C/D conduction-angle definitions are universal in US electronics textbooks.
Common pitfall: Thinking Class D is “linear” — it is a switching (nonlinear) class, just efficient.
Real on-air practice: Knowing conduction angles helps you pick the right PA class for each mode.
A、B、C、D四类放大器中的某些类型可用来线性放大音频信号。以下描述正确的是：
- A对于A类放大器，使用一支晶体管即可完整放大信号的正、负半周
- B对于B类放大器，使用二支晶体管推挽工作就可以分别放大信号的正、负半周
- C对于C类放大器，可用一支晶体管放大信号的部分周期，之后再找回丢失的信息
- D对于D类放大器，可用二支晶体管组成图腾柱，线性放大信号的正、负半周
Some of the Classes A, B, C, D amplifiers can linearly amplify an audio signal. The correct descriptions are: (Choose all that apply.)
- AFor a Class A amplifier, a single transistor can fully amplify both the positive and negative half-cycles of the signal
- BFor a Class B amplifier, two transistors operating in push-pull can separately amplify the positive and negative half-cycles
- CFor a Class C amplifier, one transistor can amplify part of the signal cycle and the lost information can later be recovered
- DFor a Class D amplifier, two transistors in a totem-pole can linearly amplify the positive and negative half-cycles
Only Classes whose devices can be arranged to track the full waveform linearly suit audio. Class A (甲类, A) with one transistor reproduces both half-cycles (A correct). Class B (乙类, B) needs two transistors in push-pull, each handling one half-cycle (B correct). Class C (丙类, C) clips most of the cycle and cannot recover the lost audio — wrong. Class D (丁类, D) is a switching (pulse-width) stage; although it can reproduce audio via filtering, the official key marks only A and B for this item (D’s “totem-pole linear amplification” description is not the standard correct statement).
US–China difference: US audio theory: single-ended Class A or push-pull Class B/AB for linear audio.
Common pitfall: Believing Class C can somehow “recover” lost half-cycles for audio.
Real on-air practice: A stereo amp uses push-pull Class AB; each transistor does one half-cycle.
A、B、C、D四类放大器都可以用来放大射频信号。关于此结论，以下描述正确的是：
- AA类和B类放大器可以线性放大输入信号，所以适合放大所有类型的射频信号
- BC类和D类放大器损失信号的幅度信息，所以仅适合放大振幅不变的射频信号
- CA类和B类放大器只能放大线性信号，不能放大通过非线性电路产生的信号
- DC类和D类放大器只能放大非线性信号，不能放大通过线性电路生成的信号
All of the Classes A, B, C, D amplifiers can be used to amplify RF signals. Regarding this conclusion, the correct descriptions are: (Choose all that apply.)
- AClasses A and B can linearly amplify the input signal, so they suit all types of RF signals
- BClasses C and D lose the amplitude information of the signal, so they only suit RF signals whose amplitude is constant
- CClasses A and B can only amplify linear signals and cannot amplify signals generated by nonlinear circuits
- DClasses C and D can only amplify nonlinear signals and cannot amplify signals generated by linear circuits
All four classes can amplify RF, but only the linear ones (甲类/乙类, Classes A/B, and AB) preserve amplitude information, so they fit any RF mode (A correct). Classes C and D are nonlinear/switching and discard amplitude detail, so they only suit constant-amplitude RF such as FM/CW (B correct). C and D wrongly restrict A/B and C/D to only one kind of source signal; any class can amplify a signal fed to it.
US–China difference: Same principle: choose linear PA for AM/SSB, nonlinear for FM/CW.
Common pitfall: Thinking a class “cannot amplify” a signal type — it can, but may distort amplitude-dependent modes.
Real on-air practice: SSB → linear PA; FM → nonlinear PA.
业余无线电爱好者经常将AB类放大器用作射频功率放大器。其特点是：
- A这种放大器稍有静态偏置电流，器件的导通角度也略大于半个信号周期
- BAB类放大器是对B类的改进。实际应用时失真低于B类，效率优于A类
- C尽管这种放大器存在一定的静态偏置电流，但是器件的通角仍然维持180°
- D这种放大器不能用于FM，其导致信号出现多对边带，载波还会时而消失
Amateur radio operators often use Class AB amplifiers as RF power amplifiers. Their characteristics are: (Choose all that apply.)
- AThis amplifier has a small quiescent bias current, and the device’s conduction angle is slightly greater than half a signal cycle
- BThe Class AB amplifier is an improvement on Class B; in practice it has less distortion than Class B and better efficiency than Class A
- CAlthough this amplifier has a certain quiescent bias current, the device’s conduction angle still remains 180°
- DThis amplifier cannot be used for FM; it causes the signal to develop multiple sideband pairs and the carrier to disappear from time to time
Class AB (甲乙类) sits between A and B: a small quiescent bias current keeps the conduction angle just over 180° (A correct), eliminating Class B crossover distortion while keeping efficiency above Class A (B correct). C is wrong because the conduction angle is slightly more than 180°, not exactly 180°. D is wrong — Class AB is widely used for FM (constant-amplitude) and does not inherently produce disappearing carriers or spurious sidebands.
US–China difference: US hams also favor Class AB RF PAs as the A/B compromise.
Common pitfall: Believing Class AB conduction angle is exactly 180° (that is pure Class B).
Real on-air practice: Most modern HF SSB/CW finals are Class AB biased just above cutoff.
尽管单管工作的B类或AB类放大器存在波形失真，会产生谐波，甚至存在一定程度的高阶互调，却可以用作发射机的末级放大器。我们对该问题的理解是：
- A放大器产生的谐波须经选频网络滤除，以确保谐波抑制满足法规要求
- B放大器的高阶互调导致工作频率周边的杂散。若有，需用负反馈解决
- C射频放大器的谐波可用发射天线滤除，无需特别关注
- D射频放大器的高阶互调，如不严重也可以打个马虎眼
Although a single-ended Class B or Class AB amplifier has waveform distortion, generates harmonics, and even has some higher-order intermodulation, it can still be used as the final amplifier of a transmitter. Our understanding of this is: (Choose all that apply.)
- AThe harmonics generated by the amplifier must be filtered out by a frequency-selective network to ensure harmonic suppression meets regulatory requirements
- BThe higher-order intermodulation of the amplifier produces spurious signals near the operating frequency; if present, they must be dealt with using negative feedback
- CThe harmonics of an RF amplifier can be filtered out by the transmitting antenna, so no special attention is needed
- DThe higher-order intermodulation of an RF amplifier can be glossed over if it is not severe
A single-ended Class B/AB final is usable because its harmonics are removed by the output 选频网络 (frequency-selective/tuned network) to satisfy 杂散发射 (spurious emission) limits (A correct). Its higher-order intermodulation creates spurs near the operating frequency, which are reduced by 负反馈 (negative feedback) (B correct). C is wrong — an antenna is not a harmonic filter and must not be relied on. D is wrong — spurious emissions are regulated and cannot be ignored.
US–China difference: FCC Part 97 also sets strict harmonic/spurious limits; a low-pass filter is required in the US.
Common pitfall: Thinking the antenna filters harmonics — it does not; a proper low-pass filter is needed.
Real on-air practice: You install a transmit low-pass filter after the PA to keep harmonics legal.
若将A、B、C、D四类放大器输出波形的失真程度由小到大排列，则以下描述正确的是：
- AA、B、C、D
- BD、C、B、A
- CA、C、B、D
- DB、A、D、C
If the output-waveform distortion of Classes A, B, C, D amplifiers is arranged from smallest to largest, the correct description is:
- AA, B, C, D
- BD, C, B, A
- CA, C, B, D
- DB, A, D, C
Distortion increases as conduction angle shrinks and the device is driven harder: Class A (甲) is least distorted, then Class B (乙), then Class C (丙), and Class D (丁) switching has the largest raw waveform error before output filtering. So the ascending order is A, B, C, D.
US–China difference: Same ordering taught in US amplifier classes.
Common pitfall: Reversing the order or placing Class D first.
Real on-air practice: Distortion order guides your PA class choice per mode.
若将A、B、C、D四类放大器用作射频功率放大，则按电源效率由高到低可以排列为：
- AD、C、B、A
- BA、B、C、D
- CD、C、A、B
- DB、A、D、C
If Classes A, B, C, D amplifiers are used as RF power amplifiers, arranged from highest to lowest power-supply efficiency they are:
- AD, C, B, A
- BA, B, C, D
- CD, C, A, B
- DB, A, D, C
Efficiency rises as the device spends more time near cutoff: 丁类 (Class D, switching) is highest, then 丙类 (Class C), then 乙类 (Class B), and 甲类 (Class A) is lowest. So the descending order is D, C, B, A.
US–China difference: Same efficiency ranking; Class D switching amps are popular in US QRP/CW rigs.
Common pitfall: Confusing this with the distortion ranking (which is the reverse).
Real on-air practice: A Class D audio amp in your rig stays cool thanks to high efficiency.
为什么B类或AB类音频放大器需要推挽工作，而相同类别的线性射频放大器却可以单管工作？
- A常见射频信号的相对带宽显著小于100%，波形中的缺失部分可用选频网络还原
- B如果待放大音频信号是窄带的，比如1kHz±100Hz，带选频的单管放大同样可行
- C射频信号不在意失真与否，功率够劲就好。音频信号如有失真，那是不可接受的
- D这显然是误解了放大器的类型。单管射频放大器必是甲类偏置的，否则肯定失真
Why do Class B or Class AB audio amplifiers need push-pull operation, while a linear RF amplifier of the same class can work with a single transistor? (Choose all that apply.)
- ACommon RF signals have a relative bandwidth significantly below 100%, so the missing portion of the waveform can be restored by a frequency-selective network
- BIf the audio signal to be amplified is narrow-band, e.g. 1 kHz ±100 Hz, single-transistor amplification with a tuned network is also feasible
- CRF signals do not care about distortion, only about enough power; audio distortion is unacceptable
- DThis obviously misreads the amplifier type; a single-transistor RF amplifier must be Class A biased, otherwise it will certainly distort
A single-ended Class B/AB RF stage clips half-cycles, but because RF is narrow-band the 选频网络 (tuned network) reconstructs the missing fundamental from the remaining energy (A correct). The same trick works for any narrow-band signal — even narrow-band audio at 1 kHz ±100 Hz could use a tuned single-ended stage (B correct). C is wrong (RF linearity still matters for SSB/AM); D is wrong (single-ended RF can be Class AB, not necessarily Class A).
US–China difference: Same concept; US single-ended RF finals rely on output tuning, while audio uses push-pull.
Common pitfall: Assuming single-ended RF must be Class A.
Real on-air practice: A tuned final rebuilds the sine even though the transistor only conducts half the time.
在A、B、C、D四类放大器中，可以用作10kHz至60MHz宽带射频信号单管线性功率放大器的类别有：（不考虑电源效率）
- AA
- BB
- CC
- DD
Among Classes A, B, C, D, which class can serve as a single-transistor linear power amplifier for a 10 kHz to 60 MHz wideband RF signal? (Power-supply efficiency not considered)
- AClass A
- BClass B
- CClass C
- DClass D
A 10 kHz–60 MHz signal spans a huge relative bandwidth (several decades), so a tuned network cannot restore missing half-cycles — the amplifier must be linear by itself. Only 甲类 (Class A) is linear in a single-transistor stage across such a bandwidth. Classes B/C/AB need push-pull or tuning; Class D is switching (nonlinear). So only Class A fits.
US–China difference: US wideband RF (e.g. SDR transmit) uses Class A or push-pull linear stages for the same reason.
Common pitfall: Forgetting that “wideband” rules out tuned-network restoration, forcing a truly linear class.
Real on-air practice: A broadband 1.8–54 MHz QRP amp is typically single-ended Class A.
在A、B、C、D四类放大器中，可以用作对讲机的FM射频功率放大器的全部类别有：（不考虑电源效率）
- AA、B、C、D
- BA、B、C
- CA、B、D
- DA
Among Classes A, B, C, D, which classes can all serve as the FM RF power amplifier of a handheld transceiver? (Power-supply efficiency not considered)
- AClasses A, B, C, D
- BClasses A, B, C
- CClasses A, B, D
- DClass A
FM (frequency modulation) is constant-amplitude, so amplitude linearity is irrelevant and any class can amplify it: Classes A, B, C, and D all work (efficiency aside). Therefore all four classes qualify, which is option A.
US–China difference: US handheld FM finals use Class C or Class D (switching) for efficiency; all classes are theoretically usable.
Common pitfall: Excluding a class just because it is nonlinear — FM does not need amplitude fidelity.
Real on-air practice: Many HT finals are Class C or Class E/D switching stages.
在A、B、C、D四类放大器中，可以用作CW射频功率放大器的全部类别有：（不考虑电源效率；假定以K=5来确定CW信号的必要带宽）
- AA、B
- BA、B、C
- CA、B、D
- DA、B、C、D
Among Classes A, B, C, D, which classes can all serve as a CW RF power amplifier? (Power-supply efficiency not considered; assume K=5 to determine the necessary bandwidth of the CW signal)
- AClasses A, B
- BClasses A, B, C
- CClasses A, B, D
- DClasses A, B, C, D
With K=5 the CW necessary bandwidth is defined and constant-amplitude keying is assumed; the official key lists only Classes A and B as the valid choices here (option A). Note that in practice Class C and switching Class D are also commonly used for CW carriers, but per this question’s answer key the selected pair is A, B.
US–China difference: US CW PAs routinely use Class C; answer keys differ by bank, so follow the given key.
Common pitfall: Over-thinking K=5 — it just fixes the CW bandwidth for the linearity assumption.
Real on-air practice: CW is on/off keying at constant amplitude, so nonlinear PAs are typical.
在A、B、C、D四类放大器中，适宜用作小信号放大器的是：
- AA
- BB
- CC
- DD
Among Classes A, B, C, D, the one suited to a small-signal amplifier is:
- AClass A
- BClass B
- CClass C
- DClass D
A small-signal stage must stay linear, so it uses 甲类 (Class A), whose device never cuts off and reproduces the signal cleanly. Classes B/C/D are power/switching stages, not small-signal pre-amps in this context.
US–China difference: Same: small-signal gain stages are Class A.
Common pitfall: Confusing small-signal class with power-amplifier class.
Real on-air practice: The first RF/IF gain blocks in a receiver are Class A.
在A、B、C、D四类放大器中，属于大信号放大器的全部类别有：
- AB、C、D
- BA、B、C、D
- CA、C、D
- DC、D
Among Classes A, B, C, D, all the classes that belong to large-signal amplifiers are:
- AClasses B, C, D
- BClasses A, B, C, D
- CClasses A, C, D
- DClasses C, D
大信号放大器 (large-signal/power amplifier) deliberately swings the device outside the linear region. Classes B, C, and D all operate with the device cutting off or switching, so they are large-signal classes (option A = B, C, D). Class A is the small-signal/linear class here and is excluded.
US–China difference: Same classification: only Class A is the pure small-signal linear class.
Common pitfall: Including Class A among large-signal classes.
Real on-air practice: Power finals are B/C/AB/D; drivers may be Class A.
很多业余无线电设备中的音频功率放大电路采用两个串联的输出功率管，分别负责音频信号正、负半周的放大。这种电路的典型名称和作用是：
- A推挽放大电路，实现极小静态偏置电流的高电源效率的线性功率放大
- B双管串联电路，得到双倍的输出电流和输出功率
- C双管串联电路，得到较高的输出阻抗以改善其与负载之间的阻抗匹配
- D双管串联电路，得到较高的输入阻抗以改善其与前级之间的阻抗匹配
Many amateur radio audio power amplifiers use two series-connected output power transistors, each handling the positive and negative half-cycle of the audio signal. The typical name and function of this circuit are:
- Aa push-pull amplifier circuit, achieving linear power amplification with very small quiescent bias current and high power-supply efficiency
- Ba two-transistor series circuit that yields double the output current and output power
- Ca two-transistor series circuit that yields higher output impedance to improve impedance matching to the load
- Da two-transistor series circuit that yields higher input impedance to improve impedance matching to the preceding stage
Two complementary (or identical) output transistors each amplifying one half-cycle form a 推挽放大电路 (push-pull amplifier). It runs with very low quiescent current (Class AB/Class B) and high efficiency while staying linear — that is option A. B/C/D misdescribe it as merely “double current/power” or as an impedance-transform trick, which is not the defining purpose.
US–China difference: Push-pull audio output is standard worldwide.
Common pitfall: Thinking the two transistors simply double current rather than share half-cycles.
Real on-air practice: The speaker output of your rig is a push-pull pair.
工作在HF频段的电子管线性放大器多采用共栅极电路形式。这种电路的优点是：
- A输入阻抗低，易于与上级电路相匹配。输入匹配网络因此得到简化或宽带化
- B栅极接地阻断了屏极与阴极间的电容耦合。放大器工作更为稳定，不易自激
- C共栅极放大形式使电路的电压放大倍数最大化
- D共栅极放大形式使电路的非线性失真最小化
HF-band vacuum-tube linear amplifiers mostly use the common-grid circuit configuration. The advantages of this circuit are: (Choose all that apply.)
- ALow input impedance, easy to match to the preceding stage; the input matching network is thus simplified or made broadband
- BThe grounded grid blocks the capacitive coupling between plate and cathode, so the amplifier is more stable and less prone to self-oscillation
- CThe common-grid configuration maximizes the circuit’s voltage gain
- DThe common-grid configuration minimizes the circuit’s nonlinear distortion
The 共栅极 (common-grid, grounded-grid) tube stage has a low input impedance that is easy to broadband-match to the driver (A correct), and grounding the grid breaks the plate–cathode capacitance feedback path, greatly improving stability against VHF/UHF self-oscillation (B correct). C is wrong (voltage gain is not maximized — common-cathode gives more gain); D is wrong (it does not minimize distortion).
US–China difference: US HF tube linears (e.g. grounded-grid 3-500Z) use the same topology for stability.
Common pitfall: Thinking common-grid gives the highest gain — it gives stability and broadband match instead.
Real on-air practice: A grounded-grid 4CX800A final is stable even on 10 m.
有时，业余无线电爱好者使用两支并联的功率管制作射频线性放大器的末级或末前级电路。这是为了：
- A双管并联，获得双倍的输出电流和输出功率
- B构成推挽电路，减小输出波形的失真
- C双管并联，得到双倍的器件耐压，减小损坏几率
- D双管并联，使各功率管的失真互相抵消，降低杂散发射
Sometimes amateur radio operators use two power transistors in parallel to build the final or driver stage of an RF linear amplifier. This is done in order to:
- Aobtain double the output current and output power by paralleling the two transistors
- Bform a push-pull circuit to reduce output waveform distortion
- Cdouble the device voltage withstand by paralleling, reducing the chance of damage
- Dlet the distortion of each transistor cancel the other, lowering spurious emission
Paralleling two power transistors shares the current, giving roughly twice the output current and thus twice the output power for a given load (A correct). Parallel is NOT push-pull (B wrong — that needs split phases); it does not double voltage rating (C wrong); and distortions do not cancel (D wrong).
US–China difference: US hams parallel MOSFETs/LDMOS for more power the same way.
Common pitfall: Confusing parallel (more current/power) with push-pull (distortion reduction).
Real on-air practice: Two parallel MRF150s give ~300 W where one gave 150 W.
放大器的负反馈是指这样的电路：
- A将放大器输出信号的一部分回输到放大器的输入端，起到抵消输入信号的作用
- B将放大器输出信号的一部分回输到放大器的输入端，起到加强输入信号的作用
- C将放大器输入信号的一部分直通到放大器的输出端，起到抵消输出信号的作用
- D将放大器输入信号的一部分直通到放大器的输出端，起到加强输出信号的作用
Negative feedback in an amplifier refers to a circuit that:
- Afeeds a portion of the amplifier output signal back to its input, acting to cancel the input signal
- Bfeeds a portion of the amplifier output signal back to its input, acting to strengthen the input signal
- Cpasses a portion of the amplifier input signal directly to its output, acting to cancel the output signal
- Dpasses a portion of the amplifier input signal directly to its output, acting to strengthen the output signal
负反馈 (negative feedback) takes a sample of the output and returns it to the input in opposite phase, partially canceling the input (A correct) — this reduces gain but improves linearity/stability. B describes positive feedback (which causes oscillation); C/D misdescribe the signal path.
US–China difference: Same definition of negative vs positive feedback in US electronics.
Common pitfall: Mixing up negative (cancels) and positive (reinforces) feedback.
Real on-air practice: Negative feedback flattens your audio amp’s response.
业余无线电设备的放大器设计大量采用负反馈技术。负反馈放大器的特点是：
- A失真小，工作稳定，但增益也有所减小
- B输入、输出阻抗易于控制，与源和负载更易匹配
- C工作带宽得以扩展，更利于实现宽带放大
- D偶次谐波等元素增加，更加适合音频放大
Amateur radio equipment makes extensive use of negative-feedback techniques in amplifier design. The characteristics of a negative-feedback amplifier are: (Choose all that apply.)
- Alow distortion and stable operation, but with somewhat reduced gain
- Binput and output impedances are easy to control, making matching to source and load easier
- Cthe operating bandwidth is extended, favoring broadband amplification
- Deven-order harmonics and similar elements increase, making it more suitable for audio amplification
Negative feedback gives lower distortion and better stability at the cost of gain (A correct), lets you set input/output impedance for easy matching (B correct), and widens bandwidth for broadband use (C correct). D is false — feedback reduces harmonics, it does not increase them.
US–China difference: Same benefits cited in US amplifier design texts.
Common pitfall: Thinking feedback increases harmonics — it suppresses them.
Real on-air practice: An op-amp IF amp uses feedback for flat gain across the band.
从能量转换的观点看，电路与负载之间的“匹配”具有如下含义：
- A电路和负载的电抗相互抵消
- B负载的电阻大小与电路所需的最优负载值一致
- C使得电路工作在恒流状态下
- D使得电路工作在恒定电压下
From the viewpoint of energy conversion, “matching” between a circuit and its load means: (Choose all that apply.)
- Athe reactances of the circuit and the load cancel each other
- Bthe load resistance equals the optimum load value required by the circuit
- Ccausing the circuit to operate in a constant-current state
- Dcausing the circuit to operate at a constant voltage
阻抗匹配 (impedance matching) means the load’s reactance cancels the source reactance (A correct, conjugate match) and the load resistance equals the source’s optimal resistance (B correct, for maximum power transfer). C and D describe constant-current/constant-voltage operation, which is not the meaning of matching.
US–China difference: Conjugate matching is the same concept in US RF practice (e.g., 50 Ω systems).
Common pitfall: Equating matching with “constant voltage/current” regulation.
Real on-air practice: A 50 Ω antenna matched to a 50 Ω transmitter delivers max power.
具有恒定内阻的信号源与负载达成阻抗“匹配”时，信号源内阻所消耗的功率：
- A与负载所得到的输出功率相等
- B是负载所得的输出功率的一半
- C对于优质信号源，这样的损耗实际为零
- D这个命题仅适用于直流电路，不适用于交流输出的信号源
When a signal source with constant internal resistance is impedance-“matched” to its load, the power dissipated in the source’s internal resistance is:
- Aequal to the output power delivered to the load
- Bhalf of the output power delivered to the load
- Ceffectively zero for a high-quality signal source
- Dthis proposition applies only to DC circuits, not to AC-output signal sources
By the maximum-power-transfer theorem, when a source of internal resistance R is matched to a load R, the load voltage equals half the open-circuit voltage, so the source and load each dissipate equal power (A correct). B/C/D are false; matching applies to both DC and AC.
US–China difference: The maximum-power-transfer theorem is identical in US circuits courses.
Common pitfall: Thinking matching wastes no source power — at match, half the power is lost internally.
Real on-air practice: At a matched 50 Ω interface, the transmitter and feeder each handle equal power.
电路的“非线性失真”是指该电路的输出信号与输入信号相比发生了下列改变：
- A产生了新的频率分量
- B各频率分量的比例发生了改变
- C信号的幅度发生了改变
- D不同频率分量的相位延迟发生了改变
A circuit’s “nonlinear distortion” means that, compared with the input signal, its output signal undergoes the following change:
- Anew frequency components are generated
- Bthe proportion among the various frequency components changes
- Cthe amplitude of the signal changes
- Dthe phase delay of different frequency components changes
非线性失真 (nonlinear distortion) specifically means the output contains frequency components not present at the input — new frequencies (harmonics, intermodulation) are created by the nonlinear transfer characteristic (A correct). B (gain change), C (amplitude change), D (phase shift) can occur in linear systems too and are not the defining feature of nonlinear distortion.
US–China difference: Same definition: nonlinear distortion = new frequency components.
Common pitfall: Calling ordinary gain or phase shift “nonlinear distortion.”
Real on-air practice: Over-driven SSB creates splatter (new frequencies) — nonlinear distortion.
有源器件可将输入的单频信号变换为波形偏离正弦或余弦形状的复杂周期信号，从而生成谐波等全新频率成分。这是一种非线性变换。下面哪些场景包含这种变换？
- A二极管检波电路输出信号的大小正比于输入射频信号的幅度
- B二极管环形调制器利用输入音频信号线性改变本振信号的振幅
- C二极管整流电路将输入交流电转换为与之相应的脉动直流电
- D流过发光二极管（LED）的正向电流与限流电阻的阻值成反比
An active device can transform a single-frequency input into a complex periodic signal whose waveform deviates from a sine/cosine, thereby generating entirely new frequency components such as harmonics. This is a nonlinear transformation. Which of the following scenarios contain such a transformation? (Choose all that apply.)
- AIn a diode detector circuit, the output magnitude is proportional to the amplitude of the input RF signal
- BA diode ring modulator uses the input audio signal to linearly vary the amplitude of the local-oscillator signal
- CA diode rectifier circuit converts input AC into corresponding pulsating DC
- DThe forward current through a light-emitting diode (LED) is inversely proportional to the value of the current-limiting resistor
A diode detector rectifies the envelope (nonlinear squaring/commutation, A), a ring modulator multiplies two signals (a nonlinear product generating sum/difference and new components, B), and a rectifier produces pulsating DC with rich harmonics (C) — all are nonlinear transformations. D is merely Ohm’s law (I = V/R) with a series resistor, a linear relationship, not a waveform-nonlinearity transformation.
US–China difference: Same nonlinear devices (detector, mixer, rectifier) in US gear.
Common pitfall: Mistaking a simple resistive (linear) relation for nonlinearity.
Real on-air practice: Your S-meter diode detector is a classic nonlinear stage.
频率为f的正弦或余弦信号与频率为f的复杂周期信号在频谱上有什么不同？
- A前者为频率为f的单一频率分量；后者为频率为f整数倍的多个频率分量
- B前者为频率为f的单一频率分量；后者为频率为f分数倍的多个频率分量
- C前者为频率为f奇数倍的多个频率分量；后者为频率为f偶数倍的多个频率分量
- D前者为连续频率分量；后者为离散频率分量
What is the spectral difference between a sinusoidal or cosine signal of frequency f and a complex periodic signal of frequency f?
- AThe former is a single frequency component at frequency f; the latter consists of multiple frequency components that are integer multiples of f
- BThe former is a single frequency component at frequency f; the latter consists of multiple frequency components that are fractional multiples of f
- CThe former consists of multiple frequency components that are odd multiples of f; the latter consists of even multiples of f
- DThe former consists of continuous frequency components; the latter of discrete frequency components
By Fourier series, a pure sinusoid/cosine of frequency f is a single spectral line at f; any complex periodic signal of fundamental f decomposes into harmonics at integer multiples (f, 2f, 3f, …) of f (A correct). Fractional multiples (B) occur only for non-periodic/inharmonic signals; C/D misstate the spectra.
US–China difference: Fourier analysis is identical in US theory.
Common pitfall: Thinking a periodic wave has fractional harmonics.
Real on-air practice: A square-wave tone contains odd harmonics you can hear as buzz.
单个无限窄脉冲的频谱特征是：
- A均匀分布的连续频率分量
- B梳状分布的离散频率分量
- C单一的减幅振荡波形
- D幅度非零的直流分量
The spectral characteristic of a single infinitely narrow pulse is:
- Auniformly distributed continuous frequency components
- Bcomb-distributed discrete frequency components
- Ca single damped oscillation waveform
- Da DC component with non-zero amplitude
A single infinitely narrow (impulse) pulse has a Fourier transform that is flat across all frequencies — a continuous spectrum with equal amplitude at every frequency (A correct). A comb of discrete lines (B) belongs to a periodic pulse train, not a single pulse.
US–China difference: Impulse spectrum is the same flat continuum in US signal theory.
Common pitfall: Confusing a single pulse (continuous) with a repeating pulse train (discrete comb).
Real on-air practice: A lightning strike is broadband — it shows up everywhere on your receiver.
只包含一个频率分量的信号是：
- A该频率的简谐信号
- B该频率的对称方波
- C该频率的减幅振荡脉冲
- D该频率的无限窄脉冲串
A signal that contains only one frequency component is:
- Athe simple harmonic (sinusoidal) signal of that frequency
- Bthe symmetric square wave of that frequency
- Cthe damped oscillation pulse of that frequency
- Dthe infinitely narrow pulse train of that frequency
Only a pure sinusoid (简谐信号, simple harmonic signal) has a single spectral line. A square wave has odd harmonics, a damped pulse has a broadband spectrum, and a pulse train has a comb of discrete lines — all contain multiple frequencies (B/C/D wrong).
US–China difference: Same: a single tone = one frequency component.
Common pitfall: Thinking a square wave at “frequency f” is single-frequency.
Real on-air practice: A clean CW carrier is a single-frequency signal; keying adds sidebands.
在整个频谱空间中具有均匀分布的连续频率分量的信号是：
- A单个无限窄脉冲
- B任意频率的正弦或余弦信号
- C任意频率的对称方波
- D任意频率的减幅振荡脉冲
A signal that has uniformly distributed continuous frequency components across the entire spectrum is:
- Aa single infinitely narrow pulse
- Ba sinusoidal or cosine signal of any frequency
- Ca symmetric square wave of any frequency
- Da damped oscillation pulse of any frequency
Across the whole spectrum, only a single infinitely narrow impulse has a perfectly flat (uniform) continuous spectrum (A correct). A sinusoid is a single line (B), a square wave is discrete odd harmonics (C), and a damped pulse is a continuous but not uniform band (D).
US–China difference: Impulse/white-noise spectrum concept is universal.
Common pitfall: Picking a sinusoid for “uniform spectrum” — it is a single line.
Real on-air practice: Broadband noise (like the impulse response) appears flat across your SDR waterfall.
某业余电台在发射单边带语音信号时，设备近旁连接至某电路的一副耳机传出了模糊不清的语音。这个电路具备哪种功能？
- A检波
- B差拍
- C变频
- D振荡
While an amateur station was transmitting an SSB voice signal, a pair of headphones connected to a certain circuit near the equipment produced muffled voice. What function does this circuit perform?
- Adetection (demodulation)
- Bbeat (beat-frequency)
- Cfrequency conversion (mixing)
- Doscillation
The headphones reproduced the SSB voice, meaning the circuit recovered the audio from the RF — that is 检波 (detection/demodulation). The transmitted SSB was being picked up and detected by the nearby circuit (e.g., a diode in the headphone lead acting as an envelope/products detector).
US–China difference: Same: detecting RF to recover audio is “detection” in both countries.
Common pitfall: Confusing detection with mixing or beating.
Real on-air practice: A “radio” crystal earpiece is just a detector — it audibly demodulates a strong nearby SSB/FM field.
某业余电台发射等辐电报时，设备近旁连接至某电路的一副耳机传出了“嘟嘟”的音频电码声。这个电路具备哪种功能？
- A差拍
- B检波
- C变频
- D振荡
While an amateur station was transmitting CW (continuous wave), a pair of headphones connected to a certain circuit near the equipment produced a “beep-beep” audio Morse tone. What function does this circuit perform?
- Abeat (beat-frequency)
- Bdetection (demodulation)
- Cfrequency conversion (mixing)
- Doscillation
CW has no audio of its own; an audible tone appears only when the received carrier beats against a local oscillator in the circuit, producing an audio 差拍 (beat frequency) equal to the difference. The nearby circuit therefore contains a local oscillator and a beat/mixer stage (a BFO/heterodyne), so the function is beat.
US–China difference: US CW receivers also use a beat-frequency oscillator (BFO) to make CW audible.
Common pitfall: Thinking CW is “detected” like AM — pure CW needs a beat to be heard.
Real on-air practice: Tune your BFO to get a comfortable ~600 Hz CW sidetone.
爱好者小强实验某个电路。接通电源时，近旁的收信机收到了类似鸟鸣的声音。断开电源，鸟鸣消失。小强的电路具备哪种功能？
- A振荡
- B差拍
- C检波
- D变频
The hobbyist Xiao-qiang was experimenting with a circuit. When powered on, a nearby receiver picked up a bird-like sound; when the power was cut, the sound disappeared. What function does Xiao-qiang’s circuit perform?
- Aoscillation
- Bbeat (beat-frequency)
- Cdetection (demodulation)
- Dfrequency conversion (mixing)
The circuit generates a signal on its own only when powered — that is 振荡 (oscillation). A self-excited oscillator radiates a tone (here warbling like a birdie) that the receiver picks up; removing power stops it. Beat/detection/mixing all require an incoming RF to act on, but here the circuit itself is the source.
US–China difference: Same: an oscillator generates RF without an input signal.
Common pitfall: Confusing an oscillator (source) with a mixer (needs two inputs).
Real on-air practice: A VFO is an oscillator; a poorly shielded one can birdie your receiver.
频率为f1、f2的两个信号流经同一个非线性元件会彼此互调，其中的三阶互调产物可能成为收信机中的假信号或发信机输出的一种杂散。三阶互调产物的频率可以计算为：
- A2f1±f2、2f2±f1
- B2f1、3f1、2f2、3f2
- Cf1±f2、2f1±2f2、3f1±3f2
- D4f1±f2、5f1±2f2、6f1±3f2……
Two signals of frequencies f1 and f2 passing through the same nonlinear element intermodulate with each other; the third-order intermodulation products may become false signals in a receiver or a kind of spurious output from a transmitter. The frequencies of the third-order intermodulation products are calculated as:
- A2f1 ± f2, 2f2 ± f1
- B2f1, 3f1, 2f2, 3f2
- Cf1 ± f2, 2f1 ± 2f2, 3f1 ± 3f2
- D4f1 ± f2, 5f1 ± 2f2, 6f1 ± 3f2 …
Third-order intermodulation (三阶互调) products from two tones are at 2f1−f2, 2f1+f2, 2f2−f1, 2f2+f1 (the combinations whose order sums to 3). These are the ones that fall close to the wanted band and cause interference, so A is correct. B lists harmonics; C lists sum/difference (mixing, second-order); D lists fifth-order products.
US–China difference: Same IMD math; US hams watch 2f1−f2 “near-end” products on repeaters.
Common pitfall: Mixing up third-order (2f1±f2) with second-order (f1±f2) products.
Real on-air practice: Two strong nearby FM signals can produce a 2f1−f2 birdie in your receiver.
术语“差拍”是指一种现象：
- A两个不同频率的信号通过非线性电路之后得到频率为两者之差的一个新信号
- B差拍、混频和二阶互调均指这一现象。称谓分开是因为应用场景不同
- C凡是接收机收到的连续音频叫声都是“差拍”
- D一个单频信号经过非线性电路得到一系列谐波信号，相邻信号的频率间隔等于单频信号的频率。这样的一簇谐波总称“差拍”
The term “beat” (差拍) refers to a phenomenon: (Choose all that apply.)
- Atwo signals of different frequencies passing through a nonlinear circuit yield a new signal whose frequency is the difference between the two
- Bbeat, mixing, and second-order intermodulation all refer to this phenomenon; the names differ only because of the application scenario
- Cany continuous audio whistle received by a receiver is a “beat”
- Da single-frequency signal passing through a nonlinear circuit yields a series of harmonics whose adjacent spacing equals the single frequency; such a cluster of harmonics is collectively called a “beat”
差拍 (beat) is the difference-frequency product of two signals through a nonlinear/multiplicative stage (A correct). Mixing (变频) and second-order intermodulation (二阶互调) are the same mathematical product (f1−f2 and f1+f2); only the context differs (B correct). C is too broad (not every whistle is a beat), and D describes harmonics, not a beat.
US–China difference: US texts also equate beat/mix/2nd-order IMD as the same multiplicative product.
Common pitfall: Calling any audible whistle a beat, or calling harmonics a beat.
Real on-air practice: Your receiver’s mixer makes a beat between the VFO and the incoming signal — that’s how it gets an IF.
业余无线电爱好者常用倍频器获取输入信号整倍频率的输出信号。倍频器的工作原理为：
- A利用有源器件的非线性使输入信号产生谐波，再用谐振电路选出所需倍频分量
- B利用线性放大器产生输入信号的系列谐波，再用谐振电路选出所需的某次倍频
- C将LC谐振电路调谐到输入信号的某个谐波频率上，所得输出既为倍频信号
- D利用标称频率等于倍频的石英晶体谐振器组成振荡器，所得输出就是倍频信号
Amateur radio operators often use a frequency multiplier to obtain an output at an integer multiple of the input frequency. The operating principle of a frequency multiplier is:
- Ause the nonlinearity of an active device to make the input signal generate harmonics, then use a resonant circuit to select the desired multiplied component
- Buse a linear amplifier to generate a series of harmonics of the input signal, then use a resonant circuit to select a desired multiple
- Ctune an LC resonant circuit to one harmonic of the input signal, and the resulting output is the multiplied signal
- Duse a quartz crystal resonator whose nominal frequency equals the multiple to form an oscillator, and the output is the multiplied signal
A 倍频器 (frequency multiplier) works by driving an active device into nonlinearity so the output contains harmonics of the input, then a tuned circuit selects the desired harmonic (e.g., 2×, 3×) (A correct). B is wrong because a linear amplifier does not generate harmonics; C is wrong because a passive tuned circuit cannot create a harmonic that is not present; D is wrong because a crystal oscillator sets its own frequency, not a multiplication of the input.
US–China difference: Same multiplier principle in US VHF/UHF transverters.
Common pitfall: Thinking a linear amp or passive filter alone can multiply frequency.
Real on-air practice: A 2× multiplier turns a 14 MHz VFO into a 28 MHz drive.
正弦交流信号通过下列哪些电路时会产生高次谐波？
- A二极管整流器
- B二极管检波器
- C二极管环形调制器
- D调谐在信号整倍频率上的选频网络
Through which of the following circuits does a sinusoidal AC signal generate higher-order harmonics? (Choose all that apply.)
- Aa diode rectifier
- Ba diode detector
- Ca diode ring modulator
- Da frequency-selective network tuned to an integer multiple of the signal
A diode rectifier (A), diode detector (B), and diode ring modulator (C) are all nonlinear and therefore create harmonics from a sine input. A passive 选频网络 (tuned network, D) only selects existing components; it cannot generate new harmonics, so it is incorrect.
US–China difference: Same: only nonlinear stages generate harmonics; filters only select.
Common pitfall: Believing a tuned circuit “creates” the harmonic it passes.
Real on-air practice: A diode in the RF path is a harmonic source to watch for.
在下列调制方式中，已调信号的振幅恒定不变的是：
- A频移键控FSK
- B频率调制FM
- C相位调制PM
- D相移键控PSK
Among the following modulation modes, those in which the modulated signal’s amplitude remains constant are: (Choose all that apply.)
- Afrequency-shift keying (FSK)
- Bfrequency modulation (FM)
- Cphase modulation (PM)
- Dphase-shift keying (PSK)
All four are angle/digital constant-envelope modulations: FSK, FM, PM, and PSK all keep a constant amplitude (the information is in frequency or phase, not envelope), so all four are correct. This is why nonlinear (Class C/D) amplifiers can be used for them.
US–China difference: Same constant-envelope property for FM/PM/FSK/PSK in US practice.
Common pitfall: Forgetting PSK/FSK are constant-amplitude like FM/PM.
Real on-air practice: RTTY (FSK) and PSK31 both run through nonlinear PAs without envelope issues.
在下列调制方式中，施加特定频率和特定幅度的调制信号可使载波分量消失的是：
- A频率调制FM
- B相位调制PM
- C抑制载波单边带幅度调制SSB
- D开关键控OOK
Among the following modulation modes, those in which applying a modulating signal of a specific frequency and specific amplitude can make the carrier component disappear are: (Choose all that apply.)
- Afrequency modulation (FM)
- Bphase modulation (PM)
- Csuppressed-carrier single-sideband amplitude modulation (SSB)
- Don-off keying (OOK)
For angle modulation (FM and PM), the carrier amplitude coefficient is the Bessel function J0(β); at certain modulation indices β (specific frequency/deviation) the carrier term J0 goes to zero — a Bessel null — so the carrier component disappears (A, B correct). SSB/DSB suppress the carrier by design (not by a specific modulation frequency/amplitude), and OOK keeps a full carrier while keyed on, so C and D are not the intended answers here.
US–China difference: US hams see Bessel-null carrier suppression on an FM deviation meter the same way.
Common pitfall: Thinking only SSB “removes the carrier” — here the question targets angle modulation nulls.
Real on-air practice: Adjusting FM deviation to a Bessel null lets you null the carrier while tuning.
在下列调制方式中，施加特定频率和特定幅度的调制信号可使某一对边带消失的是：
- A频率调制FM
- B相位调制PM
- C幅度调制AM
- D抑制载波双边带幅度调制DSB
Among the following modulation modes, those in which applying a modulating signal of a specific frequency and specific amplitude can make one pair of sidebands disappear are: (Choose all that apply.)
- Afrequency modulation (FM)
- Bphase modulation (PM)
- Camplitude modulation (AM)
- Dsuppressed-carrier double-sideband amplitude modulation (DSB)
In angle modulation the sideband amplitudes are Bessel functions Jn(β); at certain modulation indices a specific sideband pair Jn vanishes (A, B correct). For AM the two sidebands are always symmetric and present whenever modulating (C wrong); for DSB both sidebands are always present (D wrong). Thus only FM and PM fit the statement.
US–China difference: Same Bessel sideband-null behavior in US FM theory.
Common pitfall: Expecting AM sidebands to disappear — they only shrink with modulation depth.
Real on-air practice: On a deviation meter, certain Bessel nulls make specific sidebands vanish.
在下列调制方式中，已调信号的载波相位恒定不变的是：
- A幅度调制AM
- B频率调制FM
- C相移键控PSK
- D频移键控FSK
Among the following modulation modes, the one in which the modulated signal’s carrier phase remains constant is:
- Aamplitude modulation (AM)
- Bfrequency modulation (FM)
- Cphase-shift keying (PSK)
- Dfrequency-shift keying (FSK)
In 幅度调制 (AM), only the envelope amplitude varies with the message while the carrier phase stays constant (A correct). FM changes frequency (hence phase), PSK and FSK change phase/frequency, so their carrier phase is not constant (B/C/D wrong).
US–China difference: Same: AM has constant phase, angle modulations vary phase.
Common pitfall: Mixing up which parameter each modulation varies.
Real on-air practice: An AM broadcast’s carrier phase is steady; only its envelope carries audio.
在下列调制方式中，已调信号的载波幅度恒定不变的是：
- A幅度调制AM
- B频率调制FM
- C相移键控PSK
- D频移键控FSK
Among the following modulation modes, the one in which the modulated signal’s carrier amplitude remains constant is:
- Aamplitude modulation (AM)
- Bfrequency modulation (FM)
- Cphase-shift keying (PSK)
- Dfrequency-shift keying (FSK)
Per the examination key, 幅度调制 (AM) is the answer: in AM the carrier component itself retains a fixed amplitude and the information rides on the envelope, whereas FM/PM/PSK/FSK are treated here as angle/digital modulations whose “carrier” is not a fixed-amplitude reference component in the same sense. (Note: FM/PM/FSK/PSK are also constant-envelope in practice; this item keys on AM as the modulation whose carrier amplitude is the defining constant reference.)
US–China difference: Both systems distinguish AM (envelope carries info) from angle/digital constant-envelope modes.
Common pitfall: Over-generalizing “constant envelope” — follow the specific keyed distinction for this item.
Real on-air practice: AM’s carrier is always present at constant amplitude; sidebands carry the audio.
在下列调制方式中，已调信号中仅包含一组与调制信号的信息相对应的边带的是：
- A抑制载波单边带幅度调制SSB
- B幅度调制AM
- C等幅电报CW
- D抑制载波双边带幅度调制DSB
Among the following modulation modes, the one whose modulated signal contains only a single set of sidebands corresponding to the modulating information is:
- Asuppressed-carrier single-sideband amplitude modulation (SSB)
- Bamplitude modulation (AM)
- Ccontinuous wave (CW) telegraphy
- Dsuppressed-carrier double-sideband amplitude modulation (DSB)
抑制载波单边带 (SSB) transmits only one sideband (upper or lower) plus no carrier, so it carries the information in a single sideband set (A correct). AM has two sidebands + carrier; CW is a keyed carrier with keying sidebands; DSB has two sidebands — none of those is single-sideband.
US–China difference: SSB is the standard efficient phone mode in both countries.
Common pitfall: Confusing SSB (one sideband) with DSB (two sidebands).
Real on-air practice: On 20 m phone you use SSB — half the bandwidth of AM.
二极管环形调制器可以用来制作乘积检波器。这种检波器的作用是：
- A用来给CW或SSB信号检波
- B用来给FM信号检波
- C用来给调相信号检波
- D用来将话音从背景噪声中提取出来
A diode ring modulator can be used to build a product detector. The function of this detector is:
- Ato detect (demodulate) CW or SSB signals
- Bto detect (demodulate) FM signals
- Cto detect phase-modulated signals
- Dto extract speech from background noise
A 乘积检波器 (product detector) multiplies the incoming signal by a local-oscillator (BFO) signal to recover the baseband — exactly what CW and SSB need (A correct). FM needs a discriminator/quadrature detector; PM likewise needs a phase detector; “extracting speech from noise” is noise reduction, not the detector’s function.
US–China difference: US SSB/CW receivers also use a product detector (mixer + BFO).
Common pitfall: Using a product detector for FM — FM needs a discriminator.
Real on-air practice: Your SSB/CW demodulation is a product detector beating the signal against the BFO.
二极管环形调制器可以用来制作超外差式接收机的混频器。这种混频器的作用是：
- A将接收到的射频信号转换为中频信号
- B将几个电台的信号混合在一起
- C阻止中频通带以外的不必要信号
- D从一些辅助设备获取电台输入，如TNC
A diode ring modulator can be used to build the mixer of a superheterodyne receiver. The function of this mixer is:
- Ato convert the received RF signal into an intermediate-frequency (IF) signal
- Bto mix together the signals of several stations
- Cto block unwanted signals outside the IF passband
- Dto take station input from some auxiliary equipment, such as a TNC
In a 超外差式接收机 (superheterodyne receiver), the 混频器 (mixer) multiplies the incoming RF with the local-oscillator signal to produce the 中频 (IF) — the difference frequency (A correct). B describes mere summation, not frequency conversion; C is the IF filter’s job; D is unrelated.
US–China difference: Superhet architecture (RF → mixer → IF) is identical in US receivers.
Common pitfall: Confusing the mixer (frequency conversion) with the IF filter (selection).
Real on-air practice: Your receiver’s first mixer turns 14.200 MHz into a 10.7 MHz IF with the VFO.
二极管环形调制器可以用来制作外差式发射机的混频器。这种混频器的作用是：
- A将已调中频信号转换为射频信号
- B将音频基带和数字基带信号混合在一起
- C阻止通带以外不必要的信号
- D向一些辅助设备输出电台信号，如TNC
A diode ring modulator can be used to build the mixer of a heterodyne transmitter. The function of this mixer is:
- Ato convert the modulated intermediate-frequency signal into an RF signal
- Bto mix the audio baseband and digital baseband signals together
- Cto block unwanted signals outside the passband
- Dto output the station signal to some auxiliary equipment, such as a TNC
In a 外差式发射机 (heterodyne transmitter), the mixer up-converts the modulated 中频 (IF) to the final 射频 (RF) by adding/multiplying with a local oscillator (A correct). B is baseband mixing (not the IF→RF conversion); C is filtering; D is an auxiliary output, not the mixer function.
US–China difference: Transmitter up-conversion (IF→RF) is the same in US transverters.
Common pitfall: Confusing the transmit mixer’s up-conversion with audio mixing.
Real on-air practice: A 10.7 MHz SSB IF mixed with a VFO yields your 14 MHz transmit signal.
二极管环形调制器可以用来产生双边带抑制载波调幅信号。其工作原理是：
- A利用这种调制器的乘法性质，将载波与音频基带相乘，获得DSB输出
- B利用这种调制器的加法性质，将载波与音频基带相叠加，获得DSB输出
- C利用这种调制器的均方根性质，去除音频基带的极性，获得DSB输出
- D利用这种调制器的高通滤波作用，去除音频，获得射频载波和DSB输出
A diode ring modulator can be used to generate a double-sideband suppressed-carrier AM signal. Its operating principle is:
- Ause the modulator’s multiplicative property to multiply the carrier with the audio baseband, obtaining a DSB output
- Buse the modulator’s additive property to add the carrier and audio baseband together, obtaining a DSB output
- Cuse the modulator’s root-mean-square property to remove the polarity of the audio baseband, obtaining a DSB output
- Duse the modulator’s high-pass filtering to remove the audio, obtaining an RF carrier and DSB output
A ring modulator is a four-quadrant multiplier: it multiplies the carrier by the audio baseband, and the product is exactly a 抑制载波双边带 (DSB, suppressed-carrier double-sideband) signal — carrier canceled, two sidebands present (A correct). Addition (B) gives ordinary AM with a carrier; C/D misdescribe the operation.
US–China difference: Ring modulators make DSB in US sideband generators the same way.
Common pitfall: Thinking a ring modulator “adds” — it multiplies.
Real on-air practice: A DSB stage feeds a sideband filter to become SSB.
二极管环形调制器可以用来产生载波不受抑制的普通AM信号。其工作原理是：
- A只需为输入基带适当叠加直流分量，使基带极性不发生反转，即可获得AM输出
- B只需在输入基带上适当叠加导频分量，使载波极性不停反转，即可获得AM输出
- C只需增加载波的输入功率，迫使调制器的输出出现载波泄漏，即可获得AM输出
- D只需调转调制器的输入和输出端口，即可获得AM输出
A diode ring modulator can be used to generate ordinary AM (amplitude modulation) signals with an unsuppressed carrier. Its working principle is:
- Asimply add a suitable DC component to the baseband input so that the baseband polarity does not reverse, to obtain an AM output
- Bsimply add a suitable pilot component to the baseband input so that the carrier polarity keeps reversing, to obtain an AM output
- Csimply increase the carrier input power to force carrier leakage at the modulator output, to obtain an AM output
- Dsimply swap the modulator’s input and output ports, to obtain an AM output
A diode ring modulator by default produces a double-sideband suppressed-carrier (DSB-SC) signal because the carrier terms cancel. To obtain ordinary AM with a transmitted carrier, you bias the baseband with a DC offset so its sign never reverses; this adds a carrier component to the output (A). Options B (pilot/reversing carrier), C (forcing leakage via power), and D (swapping ports) do not yield proper AM.
US–China difference: The same ring-modulator principle applies worldwide; US hams also build DSB/AM with diode rings.
Common pitfall: Thinking a ring modulator naturally outputs AM — without a DC bias it produces suppressed-carrier DSB.
Real on-air practice: Adding a carrier oscillator or DC offset to a product detector/modulator recovers listenable AM.
构成振荡器的必备元素是：
- A放大倍数大于1的放大器、正反馈电路
- B放大倍数大于1的放大器、负反馈电路
- CLC或晶体谐振电路、正反馈电路
- D任意放大器、LC或晶体谐振电路
The essential elements for constituting an oscillator are:
- Aan amplifier with gain greater than 1, and a positive-feedback circuit
- Ban amplifier with gain greater than 1, and a negative-feedback circuit
- Can LC or crystal resonant circuit, and a positive-feedback circuit
- Dany amplifier, and an LC or crystal resonant circuit
Per the Barkhausen criterion, an oscillator needs an amplifier with loop gain greater than 1 plus a positive-feedback path that sets the frequency (A). Negative feedback (B) stabilizes but does not oscillate; C lacks the required gain; D omits the gain requirement entirely.
US–China difference: The gain-plus-positive-feedback rule is universal; US VFO/VCO designs follow the same criterion.
Common pitfall: Forgetting the gain > 1 requirement, or confusing positive feedback (oscillation) with negative feedback (stability).
Real on-air practice: Your transceiver’s VFO is an amplifier + feedback network sustaining the carrier frequency.
在SSB接收机的天线端口插入一段导线，导线的另一端靠近一个晶体管LC振荡电路去尝试接收。振荡器通电后，所收信号的音调会从低到高或从高到低持续变化。主要原因是：
- A元器件通电发热使电路整体的LC参数不断变化，导致频率漂移
- B晶体管正处在老化过程中。这种电路越用越稳定
- C接收机将收到的声音回馈至电路板，为振荡器额外增添了能量
- D射频能量不断对外辐射，致使电路的输出功率不断下降
Inserting a wire at the SSB (single sideband) receiver’s antenna port, with the other end placed near a transistor LC oscillator circuit to try to receive it: after the oscillator is powered on, the received tone continuously changes from low to high or high to low. The main reason is:
- Athe components heat up after power-on, causing the LC parameters of the whole circuit to keep changing, which leads to frequency drift
- Bthe transistor is in the process of aging; this kind of circuit becomes more stable the more it is used
- Cthe receiver feeds the received sound back onto the circuit board, adding extra energy to the oscillator
- Dthe RF energy keeps radiating outward, causing the circuit’s output power to keep dropping
The classic warm-up “drift” of a simple LC oscillator is caused by component heating after switch-on, which changes the inductance/capacitance values and thus the resonant frequency (A). B (aging) is a long-term effect, not the immediate tone sweep; C and D describe feedback/power loss, not the pitch glide.
US–China difference: Same drift phenomenon; US hams use TCXO/OCXO to avoid it.
Common pitfall: Mistaking the warm-up drift for a fault rather than normal thermal settling of an LC oscillator.
Real on-air practice: Let a homebrew VFO warm up a few minutes before a CW contact so the pitch stabilizes.
计量术语”ppm”经常出现在发射设备参数规格书或是业余无线电文献中。其涵义为：
- A“百万分之几”，描述电台设备的频率容限
- B“每分钟脉冲数”，描述随机过程的观察结果
- C“每分钟点数”，描述太阳黑子的发生频度
- D“预防性计划维护”，描述电台设备的维护策略
The metrological term “ppm” frequently appears in transmitter equipment spec sheets or amateur radio literature. It means:
- A“parts per million,” describing the station equipment’s frequency tolerance
- B“pulses per minute,” describing observations of a random process
- C“points per minute,” describing sunspot occurrence frequency
- D“planned preventive maintenance,” describing the station equipment’s maintenance strategy
ppm stands for “parts per million” (百万分之几) and is the standard unit for 频率容限 (frequency tolerance) — e.g., ±2.5 ppm. B/C/D are unrelated expansions of the letters.
US–China difference: The US also states frequency stability in ppm on FCC forms and rig specs.
Common pitfall: Confusing ppm (frequency tolerance) with “pulses per minute” or maintenance terms.
Real on-air practice: A ±1 ppm OCXO keeps your 14 MHz signal within ~14 Hz — well inside the band.
有时，我们会在业余收发信机的面板上或功能菜单中看到缩写为VFO的功能。它代表：
- A可变频率振荡器
- B收发信机的主载波频率可以通过旋钮自由调谐
- C石英晶体振荡器
- D可变频率石英晶体振荡器
Sometimes we see a function abbreviated VFO on the panel or in the function menu of an amateur transceiver. It stands for: (Choose all that apply.)
- Avariable frequency oscillator
- Bthe transceiver’s main carrier frequency can be freely tuned by a knob
- Cquartz crystal oscillator
- Dvariable-frequency crystal oscillator
VFO stands for 可变频率振荡器 (variable frequency oscillator) — an oscillator whose frequency you can tune freely, typically via a knob, setting the transceiver’s main carrier (A and B both describe it correctly). C is a crystal oscillator (XTAL/OCXO), and D is a VXO (variable-frequency crystal oscillator), not a plain VFO.
US–China difference: VFO is the same concept in US rigs; “VFO A/B” lets you store two tuning frequencies.
Common pitfall: Mixing up VFO (tunable oscillator) with VXO (crystal-based) or a fixed crystal oscillator.
Real on-air practice: Turning the VFO knob is how you tune across the 20 m band to find a CQ.
有时，我们会在业余自制的收发信机或其电路图中看到缩写为VXO的功能或电路组件。它代表：
- A可变频率石英晶体振荡器
- B可变频率振荡器
- C石英晶体振荡器
- D压控振荡器
Sometimes we see a function or circuit block abbreviated VXO in a homebrew amateur transceiver or its schematic. It stands for:
- Avariable-frequency crystal oscillator
- Bvariable frequency oscillator
- Cquartz crystal oscillator
- Dvoltage-controlled oscillator
VXO stands for 可变频率石英晶体振荡器 (variable-frequency crystal oscillator) — a crystal oscillator whose frequency is pulled slightly with a varactor (A). B is a VFO, C is a plain crystal oscillator (XTAL), D is a VCO.
US–China difference: VXOs are common in simple CW kits on both sides of the Pacific.
Common pitfall: Confusing VXO (crystal, narrow pull) with VFO or VCO.
Real on-air practice: A VXO gives a crystal’s stability with just enough tuning to work a few kHz of the band.
有时，我们会在业余无线电文献或某设备的电路图中看到缩写为VCO的电路。它代表：
- A压控振荡器
- B可变频率石英晶体振荡器
- C可变频率振荡器
- D石英晶体振荡器
Sometimes we see a circuit abbreviated VCO in amateur radio literature or a device schematic. It stands for:
- Avoltage-controlled oscillator
- Bvariable-frequency crystal oscillator
- Cvariable frequency oscillator
- Dquartz crystal oscillator
VCO stands for 压控振荡器 (voltage-controlled oscillator) — its frequency is set by a control voltage (A). B is VXO, C is VFO, D is a crystal oscillator (XTAL).
US–China difference: VCOs are universal; in PLL synthesizers they serve as the tuning element.
Common pitfall: Mixing VCO with VFO/VXO terminology.
Real on-air practice: Your PLL’s VCO is the part whose voltage is steered to land on 7.050 MHz.
有时，我们会在业余无线电文献或某设备的电路图中看到缩写为XTAL的元件。它代表：
- A石英晶体谐振器
- B可变频率振荡器
- C石英晶体振荡器
- D压控振荡器
Sometimes we see a component abbreviated XTAL in amateur radio literature or a device schematic. It stands for:
- Aquartz crystal resonator
- Bvariable frequency oscillator
- Cquartz crystal oscillator
- Dvoltage-controlled oscillator
XTAL stands for 石英晶体谐振器 (quartz crystal resonator) — the passive two-terminal piezoelectric element used in oscillators and filters (A). C (石英晶体振荡器) is a complete crystal oscillator module; B is VFO, D is VCO.
US–China difference: XTAL marks the same passive crystal in schematics worldwide.
Common pitfall: Conflating the bare resonator (XTAL) with a complete oscillator can (which includes an amplifier).
Real on-air practice: The 10.000 MHz XTAL in your reference oscillator sets your rig’s accuracy.
为提升无线电设备的频率稳定度，人们研制了多种高Q值压电谐振元件。考虑这类元件多可做成振荡器，则下列常见振荡器按频率稳定度由低到高可以排列为：
- ARC振荡器，LC振荡器，陶瓷振子振荡器，石英声表面波振荡器，石英晶体振荡器
- BLC振荡器，RC振荡器，陶瓷振子振荡器，石英声表面波振荡器，石英晶体振荡器
- CRC振荡器，LC振荡器，石英声表面波振荡器，石英晶体振荡器，陶瓷振子振荡器
- DRC振荡器，陶瓷振子振荡器，LC振荡器，石英晶体振荡器，石英声表面波振荡器
To improve the frequency stability of radio equipment, various high-Q (quality factor) piezoelectric resonator elements have been developed. Considering such elements can mostly be made into oscillators, the following common oscillators arranged from lowest to highest frequency stability are:
- ARC oscillator, LC oscillator, ceramic-resonator oscillator, quartz SAW (surface-acoustic-wave) oscillator, quartz crystal oscillator
- BLC oscillator, RC oscillator, ceramic-resonator oscillator, quartz SAW oscillator, quartz crystal oscillator
- CRC oscillator, LC oscillator, quartz SAW oscillator, quartz crystal oscillator, ceramic-resonator oscillator
- DRC oscillator, ceramic-resonator oscillator, LC oscillator, quartz crystal oscillator, quartz SAW oscillator
Frequency stability rises with Q and temperature stability: RC (lowest) < LC < ceramic resonator (陶瓷振子) < quartz SAW (石英声表面波) < quartz crystal (highest). A gives the correct ascending order. B wrongly puts LC below RC; C/D misplace the ceramic and SAW ranks.
US–China difference: Same stability hierarchy used in US equipment design.
Common pitfall: Forgetting that RC oscillators are the least stable and quartz crystals the most.
Real on-air practice: A TCXO/OCXO (quartz) keeps your signal locked; an RC VFO would drift off frequency.
关于高配置无线电通信设备的说明书中提到的TCXO或OCXO，以下描述正确的是：
- ATCXO指温度补偿式晶体振荡器；OCXO指恒温控制式晶体振荡器
- BOCXO的频率稳定度优于TCXO
- CTCXO指中频数字信号处理部件；OCXO指音频数字信号处理部件
- DTCXO和OCXO所处理的都是以复数表示的同相/正交样本序列
Regarding TCXO or OCXO mentioned in the manuals of high-end radio communication equipment, the following descriptions are correct: (Choose all that apply.)
- ATCXO stands for temperature-compensated crystal oscillator; OCXO stands for oven-controlled crystal oscillator
- BOCXO’s frequency stability is better than TCXO’s
- CTCXO refers to an IF digital signal-processing block; OCXO refers to an audio digital signal-processing block
- DBoth TCXO and OCXO process in-phase/quadrature (I/Q) sample sequences represented as complex numbers
TCXO = 温度补偿式晶体振荡器 (temperature-compensated crystal oscillator); OCXO = 恒温控制式晶体振荡器 (oven-controlled crystal oscillator) (A). Because an oven holds the crystal at a constant temperature, OCXO achieves better stability than TCXO (B). C and D wrongly describe them as DSP/I-Q blocks.
US–China difference: High-end US HF rigs likewise offer TCXO/OCXO options for better stability.
Common pitfall: Thinking TCXO and OCXO are digital signal-processing terms rather than oscillator types.
Real on-air practice: A station running weak-signal EME uses an OCXO so its frequency stays put for the long path.
虽然电路中的非线性失真主要来自有源器件，但是无源滤波器中的电感或变压器在其磁芯趋于饱和时也会产生同样的失真。此外，包含多个频率分量的信号通过滤波器后还会发生线性失真。这种失真可能包括：
- A频率失真
- B相位失真
- C偶次谐波
- D奇次谐波
Although nonlinear distortion in a circuit mainly comes from active devices, the inductors or transformers in passive filters can also produce the same distortion when their magnetic cores approach saturation. In addition, a signal containing multiple frequency components will also undergo linear distortion after passing through a filter. Such distortion may include: (Choose all that apply.)
- Afrequency (amplitude) distortion
- Bphase distortion
- Ceven-order harmonics
- Dodd-order harmonics
The question’s “这种失真” (this distortion) refers to the 线性失真 (linear distortion) a multi-tone signal suffers in a filter, which is amplitude/frequency distortion (频率失真) and phase distortion (相位失真) — A and B. Harmonics (C, D) are products of nonlinear (e.g., core-saturation) distortion, not linear distortion.
US–China difference: The linear-vs-nonlinear distortion distinction is the same in US electronics training.
Common pitfall: Listing harmonics as “linear” distortion — harmonics only arise from nonlinearity.
Real on-air practice: Group-delay (phase) distortion in a filter can smear a digital mode’s eye diagram.
电路的”相位失真”是指该电路的输出信号与输入信号相比发生了下列改变：
- A不同频率分量的相位延迟发生了改变
- B产生了新的频率分量
- C各频率分量的比例发生了变化
- D信号的幅度发生了改变
A circuit’s “phase distortion” means the output signal, compared with the input, undergoes the following change:
- Athe phase delay of different frequency components changes
- Bnew frequency components are produced
- Cthe proportion of each frequency component changes
- Dthe signal’s amplitude changes
相位失真 (phase distortion) means different frequency components experience different phase delays (non-constant group delay) — A. B describes nonlinear distortion (harmonics), C is frequency/amplitude distortion, D is a flat amplitude change.
US–China difference: Phase distortion is taught identically in US communications-electronics courses.
Common pitfall: Mixing phase distortion with frequency (amplitude) distortion.
Real on-air practice: Excessive phase distortion in an audio filter can muddy SSB intelligibility.
电路的”频率失真”是指该电路的输出信号波形与输入信号相比发生了如下变化：
- A各频率分量的比例发生了变化
- B信号的幅度发生了改变
- C产生了新的频率分量
- D不同频率分量的相位延迟发生了改变
A circuit’s “frequency distortion” means the output signal waveform, compared with the input, undergoes the following change:
- Athe proportion of each frequency component changes
- Bthe signal’s amplitude changes
- Cnew frequency components are produced
- Dthe phase delay of different frequency components changes
频率失真 (frequency / amplitude distortion) means the relative amplitudes of the frequency components change (the circuit’s gain varies with frequency) — A. B is an overall gain change, C is nonlinear distortion, D is phase distortion.
US–China difference: Same definition in US electronics; “amplitude distortion” is the synonymous term.
Common pitfall: Confusing frequency distortion with phase distortion or with overall level change.
Real on-air practice: A low-pass that droops at 3 kHz would frequency-distort your SSB audio.
组装业余收发信机时，爱好者常用谐振回路来筛选特定频率的信号。组成谐振回路的主要元件包括：
- A电容和电感的组合
- B电阻和电容的组合
- C电感和电阻的组合
- D半导体三极管和电阻的组合
When assembling an amateur transceiver, hams often use resonant circuits (tank circuits) to select signals of a specific frequency. The main components forming a resonant circuit include:
- Aa combination of capacitance and inductance
- Ba combination of resistance and capacitance
- Ca combination of inductance and resistance
- Da combination of a semiconductor transistor and resistance
A resonant (tank) circuit is formed by an inductor and a capacitor (LC) — A. RC/RL pairs do not resonate; a transistor+resistor is an amplifier stage, not a resonator.
US–China difference: LC tank circuits are universal in US HF/VHF kit building.
Common pitfall: Thinking any R-C or R-L pair is a “resonant” circuit.
Real on-air practice: The LC tank in your receiver’s front end selects the band you’re tuned to.
制作倍频器会用到高性能带通滤波器或是某种选择性优良的LC谐振回路。下列LC回路中，选择性最佳的是：
- A松耦合的高Q单调谐或同频双调谐回路
- B紧耦合高Q同频双调谐回路
- C松耦合低Q同频双调谐回路
- D松耦合高Q参差调谐回路
Building a frequency multiplier uses a high-performance band-pass filter or some LC resonant circuit with excellent selectivity. Among the following LC circuits, the one with the best selectivity is:
- Aa loosely coupled high-Q single-tuned or same-frequency double-tuned circuit
- Ba tightly coupled high-Q same-frequency double-tuned circuit
- Ca loosely coupled low-Q same-frequency double-tuned circuit
- Da loosely coupled high-Q staggered-tuned circuit
Selectivity is best with a high Q (quality factor) and loose coupling, which keeps the passband narrow and the skirt steep — A. Tight coupling (B) broadens the response; low-Q (C) widens it; staggered tuning (D) is deliberately wideband, reducing selectivity.
US–China difference: Same selectivity principles apply to US VHF cavity filters and HF IF filters.
Common pitfall: Assuming tighter coupling always improves a filter — it actually widens bandwidth.
Real on-air practice: A high-Q crystal filter gives your rig the selectivity to pull a weak station out of QRM.
低通滤波器的”截止频率”是指：
- A滤波器的频率响应从相对于通带的0dB下降3dB时的频率
- B高于该频率的信号将被滤波器完全切除
- C低于该频率的信号将被滤波器完全切除
- D高于该频率的信号会在滤波器中发生非线性失真
The “cutoff frequency” of a low-pass filter refers to:
- Athe frequency at which the filter’s frequency response has dropped by 3 dB relative to the passband’s 0 dB
- Bsignals above this frequency will be completely cut off by the filter
- Csignals below this frequency will be completely cut off by the filter
- Dsignals above this frequency will undergo nonlinear distortion in the filter
截止频率 (cutoff frequency) is defined as the −3 dB point: where the response falls 3 dB below the passband level (A). A real filter does not hard-cut above it (B), and it passes (not cuts) below it (C); D confuses cutoff with distortion.
US–China difference: The −3 dB cutoff definition is identical in US filter specs.
Common pitfall: Thinking the cutoff is a brick-wall frequency where everything above vanishes.
Real on-air practice: Your rig’s 2.7 kHz SSB filter has its −3 dB edges at roughly those tones.
带通滤波器的”3dB带宽”是指：
- A在通带中心频率的两侧，通带响应下降3dB时两个频率之间的间隔
- B输出信号相对于输入信号衰减3dB以上（含3dB）时的频带宽度
- C输出信号相对于输入信号衰减3dB以下（含3dB）时的频带宽度
- D滤波器维持3dB增益时的频带宽度
The “3 dB bandwidth” of a band-pass filter refers to:
- Athe interval between the two frequencies, on either side of the passband center frequency, at which the passband response drops by 3 dB
- Bthe bandwidth over which the output signal is attenuated by 3 dB or more (including 3 dB) relative to the input
- Cthe bandwidth over which the output signal is attenuated by 3 dB or less (including 3 dB) relative to the input
- Dthe bandwidth over which the filter maintains 3 dB of gain
3 dB bandwidth is the width between the two −3 dB points measured around the center frequency (A). B describes the stopband/reject region, not the bandwidth; C inverts the sense; D misstates gain.
US–China difference: 3 dB bandwidth is defined the same way in US filter data sheets.
Common pitfall: Taking “3 dB bandwidth” to mean the stopband rather than the passband width.
Real on-air practice: A 2.7 kHz CW filter’s 3 dB bandwidth sets how wide a signal sounds on receive.
滤波器有一个称为”通带波动”的参数，是指：
- A滤波器在通带范围内的衰减特性变化幅度
- B滤波器频率特性在整个频谱范围内的变化趋势
- CCW信号通过滤波器时键控边沿附近的信号幅度发生抖动的现象
- D滤波器因元器件不稳定等随机因素而使输出信号增益波动的现象
A filter has a parameter called “passband ripple.” It refers to:
- Athe magnitude of variation of the filter’s attenuation characteristics within the passband
- Bthe trend of the filter’s frequency characteristics across the entire spectrum
- Cthe phenomenon where the signal amplitude near the keying edge jitters when a CW signal passes through the filter
- Dthe phenomenon where the output signal gain fluctuates due to random factors such as component instability
通带波动 (passband ripple) is the variation (peak-to-peak) of insertion loss/gain across the passband (A). B describes overall response shape; C/D describe unrelated time-domain or random effects.
US–China difference: Passband ripple (e.g., 0.1 dB) is quoted the same way on US filter datasheets.
Common pitfall: Confusing ripple (passband variation) with overall stopband attenuation.
Real on-air practice: An elliptical CW filter may show a few dB of ripple across its passband.
在描述收信机的波段预选滤波电路和发信机的输出滤波电路时，有些技术文档（比如：服务手册）会提及LC滤波器的”阶数”或”极点数”。确定LC滤波器阶数的简单方法是：
- A先合并化简串、并联的电容和电感元件，再将串、并联的LC谐振电路视为单一组件，这样得到的电容、电感或LC谐振组件的总数即为阶数。例如，某3阶低通滤波器包含两个电容和一个电感；某3阶带通滤波器包含两个并联谐振电路和一个串联谐振电路。
- B滤波电路中分叉节的数量即为阶数
- C滤波电路中分叉节的数量减1即为阶数
- D滤波电路中电感元件的总数减去电容元件的总数即得阶数
When describing a receiver’s band-preselection filter and a transmitter’s output filter, some technical documents (e.g., service manuals) mention the “order” or “number of poles” of an LC filter. A simple method to determine the order of an LC filter is: (Choose all that apply.)
- Afirst combine and simplify series- and parallel-connected capacitor and inductor elements, then treat each series or parallel LC resonant circuit as a single component; the total number of capacitor, inductor, or LC resonant components obtained this way is the order. For example, a 3rd-order low-pass filter contains two capacitors and one inductor; a 3rd-order band-pass filter contains two parallel resonant circuits and one series resonant circuit.
- Bthe number of branching sections in the filter circuit is the order
- Cthe number of branching sections in the filter circuit minus one is the order
- Dthe total number of inductor elements minus the total number of capacitor elements in the filter circuit gives the order
The order (pole count) of an LC filter equals the number of independent reactive energy-storage elements after simplification — A gives the rigorous method and the correct examples (a 3rd-order low-pass = 2 capacitors + 1 inductor; a 3rd-order band-pass = 3 resonant sections). The official answer key also marks B (“the number of branching sections is the order”), which in many ladder/lattice filter texts coincides with the reactive-element count. C and D are incorrect formulas.
US–China difference: Filter “order/poles” means the same thing in US RF engineering.
Common pitfall: Subtracting caps from inductors (D) or subtracting one from the section count (C) to get the order.
Real on-air practice: A 5-pole crystal filter in your IF strip gives sharper selectivity than a 3-pole one.
假设业余中继台的收、发信机共用一副天线，上行和下行频率分别为F1和F2。在架设该台时，为了防止发信机的射频输出阻塞收信机的正常接收，可用措施为：
- A在发信机与天线间串联中心频率为F1的带阻滤波器，在收信机与天线间串接中心频率为F2的带阻滤波器
- B在发信机与天线间串联中心频率为F1的带通滤波器，在收信机与天线间串接中心频率为F2的带通滤波器
- C在发信机与天线间串联中心频率为F2的带阻滤波器，在收信机与天线间串接中心频率为F2的带阻滤波器
- D在发信机与天线间串联中心频率为F1的带阻滤波器，在收信机与天线间串接中心频率为F1的带阻滤波器
Suppose an amateur repeater’s receiver and transmitter share one antenna, with uplink and downlink frequencies F1 and F2 respectively. When installing this station, to prevent the transmitter’s RF output from blocking (desensitizing) the receiver’s normal reception, the usable measures are:
- Aconnect a band-reject filter with center frequency F1 in series between the transmitter and the antenna, and connect a band-reject filter with center frequency F2 in series between the receiver and the antenna
- Bconnect a band-pass filter with center frequency F1 in series between the transmitter and the antenna, and connect a band-pass filter with center frequency F2 in series between the receiver and the antenna
- Cconnect a band-reject filter with center frequency F2 in series between the transmitter and the antenna, and connect a band-reject filter with center frequency F2 in series between the receiver and the antenna
- Dconnect a band-reject filter with center frequency F1 in series between the transmitter and the antenna, and connect a band-reject filter with center frequency F1 in series between the receiver and the antenna
The repeater receives on the uplink F1 and transmits on the downlink F2. To isolate them, the transmitter leg rejects the receiver’s frequency F1 (so incoming F1 isn’t lost into the TX), and the receiver leg rejects the transmitter’s frequency F2 (so the strong TX output doesn’t block the RX) — both using band-reject (notch) filters (A). B uses band-pass (wrong sense), C/D use mismatched center frequencies.
US–China difference: US repeaters use the same duplexer principle (cavity filters notch the opposite frequency).
Common pitfall: Using band-pass instead of band-reject filters, or matching the wrong frequency to each port.
Real on-air practice: A cavity duplexer lets one antenna carry both your 145.000 MHz TX and 144.400 MHz RX.
要防止HF业余电台发出的射频能量干扰布放在天线附近的电话机，可在电话机与电话线之间串联：
- A截止频率不高于1MHz的低通滤波器
- B截止频率约为3kHz的高通滤波器
- C截止频率约为3kHz的带阻滤波器
- D中心频率约为3kHz的带通滤波器
To prevent the RF energy emitted by an HF amateur station from interfering with a telephone placed near the antenna, you can connect in series between the telephone and the telephone line:
- Aa low-pass filter with cutoff frequency not higher than 1 MHz
- Ba high-pass filter with cutoff frequency about 3 kHz
- Ca band-reject filter with cutoff frequency about 3 kHz
- Da band-pass filter with center frequency about 3 kHz
HF RF (3–30 MHz) is getting onto the phone line. A low-pass filter with cutoff ≤1 MHz passes the audio band (<4 kHz) but blocks the HF RF from entering the line (A). A high-pass (B) would pass the RF; a 3 kHz band-reject/band-pass (C/D) addresses audio, not HF.
US–China difference: US hams also fit RF chokes / line filters on phone lines near HF antennas.
Common pitfall: Picking a high-pass filter, which would let the HF RF through instead of blocking it.
Real on-air practice: A ferrite choke or 1 MHz LPF on the phone line stops your 40 m signal from buzzing the handset.
如果HF业余电台的正常发射干扰天线附近的VHF电视机，可能的解决方案是：
- A在电视机的天线输入端安装截止频率不低于30MHz的高通滤波器
- B在业余电台的发射机输出端安装截止频率不低于30MHz的高通滤波器
- C在电视机的天线输入端安装截止频率不高于300MHz的低通滤波器
- D在业余电台的发射机输出端安装截止频率不低于30MHz的低通滤波器
If the normal transmission of an HF amateur station interferes with a VHF television near the antenna, a possible solution is:
- Ainstall a high-pass filter with cutoff frequency not lower than 30 MHz at the TV’s antenna input
- Binstall a high-pass filter with cutoff frequency not lower than 30 MHz at the amateur station’s transmitter output
- Cinstall a low-pass filter with cutoff frequency not higher than 300 MHz at the TV’s antenna input
- Dinstall a low-pass filter with cutoff frequency not lower than 30 MHz at the amateur station’s transmitter output
The HF signal (≤30 MHz) is overloading the TV’s VHF tuner. A high-pass filter at the TV input, passing VHF (>30 MHz) but rejecting HF, fixes it (A). A high-pass at the transmitter (B) would block the ham’s own HF; a low-pass at the TV (C) would block VHF; a low-pass at the TX (D) is wrong type/frequency.
US–China difference: US hams similarly add a high-pass “broadcast-filter” at the TV antenna to kill HF breakthrough.
Common pitfall: Putting the filter at the transmitter instead of at the victim (TV) input.
Real on-air practice: A >30 MHz high-pass on the TV lead stops your 20 m signal from snowing the picture.
如果50Hz交流电通过全波整流器加到电阻负载上，负载两端的波形为？
- A频率为100Hz的脉动直流电
- B频率为50Hz的脉动直流电
- C稳定的直流电压
- D纯正的50Hz正弦波
If 50 Hz AC passes through a full-wave rectifier and is applied to a resistive load, what is the waveform across the load?
- Apulsating DC at 100 Hz
- Bpulsating DC at 50 Hz
- Ca stable DC voltage
- Da pure 50 Hz sine wave
Full-wave rectification flips both halves of the 50 Hz AC, so the output ripple repeats twice per AC cycle — 100 Hz pulsating DC (A). Half-wave would give 50 Hz (B); a stable DC (C) needs filtering; D is the original input.
US–China difference: Same 2× line-frequency ripple rule for full-wave rectifiers everywhere.
Common pitfall: Forgetting that full-wave doubles the ripple frequency to 100 Hz.
Real on-air practice: Your 13.8 V supply’s 100 Hz ripple is what filter caps smooth out.
在整流滤波电路中，泄放电阻的作用是：
- A关机后泄放滤波电容两端的电压
- B关机后泄放变压器绕组反激电压
- C为电源提供负载，稳定工作效率
- D过压时迅速熔断，保护滤波电容
In a rectifier-filter circuit, the role of the bleed resistor is:
- Ato discharge the voltage across the filter capacitor after power-off
- Bto discharge the transformer winding’s flyback voltage after power-off
- Cto provide a load for the power supply and stabilize its working efficiency
- Dto blow quickly when overvoltage occurs, protecting the filter capacitor
泄放电阻 (bleed resistor) safely discharges the charged filter capacitor after the supply is switched off, preventing a shock (A). B addresses flyback (a snubber’s job); C is a permanent load/resistor; D is a fuse’s job.
US–China difference: Bleed resistors serve the same safety purpose in US power supplies.
Common pitfall: Thinking the bleed resistor is a fuse or a main load resistor.
Real on-air practice: After turning off your linear supply, the bleed resistor drains the big caps so you don’t get bit.
制作开关电源或是驱动继电器的电路，甚至是在制作驱动指示灯的电路时，我们都期望电路中起控制作用的晶体管工作于开关状态。这是因为：
- A晶体管工作于开关状态时具有导通电阻小，功率损耗低的优点
- B晶体管工作于开关状态时具有工作速度快，射频干扰小的优点
- C晶体管工作于开关状态时具有电路线性好，互调杂散少的优点
- D晶体管工作于开关状态时具有驱动电压低，容性电流小的优点
When building a switching power supply, a relay-driving circuit, or even an indicator-lamp-driving circuit, we want the controlling transistor to operate in the switching state. This is because:
- Aa transistor in the switching state has the advantages of small on-resistance and low power loss
- Ba transistor in the switching state has the advantages of high speed and low RF interference
- Ca transistor in the switching state has the advantages of good circuit linearity and few intermodulation/spurious products
- Da transistor in the switching state has the advantages of low drive voltage and small capacitive current
In saturation/cutoff (switching), the transistor is either nearly a short (low on-resistance) or open, so I×V across it stays tiny and power loss is low (A). Switching actually generates more RFI (B false), is highly nonlinear (C false), and needs drive/charge (D false).
US–China difference: Switch-mode efficiency reasoning is identical in US designs.
Common pitfall: Thinking switching transistors produce less RFI — fast edges are a major noise source.
Real on-air practice: A MOSFET hard-switching in your PS stays cool; its edges are why you need ferrite chokes.
在给业余收发信机供电的电源装置中，开关电源可以比变压器降压的线性电源更为轻巧。原因是：
- A开关电源中的隔离变压器工作频率远高于工频，磁芯截面积因此减小，绕组匝数变少
- B开关电源中的半导体器件工作于开关状态，工作效率高，散热装置因此变得轻巧
- C开关电源的工作原理比线性电源简单得多，设备中的元件数量因此大幅减少
- D开关电源所用的PWM技术工作安静无噪声，无需EMC措施，设备体积因此减小
In the power supply for an amateur transceiver, a switching power supply can be more compact and lightweight than a transformer-step-down linear power supply. The reason is: (Choose all that apply.)
- Athe isolation transformer in a switching power supply operates at a frequency far above the power-line frequency, so its core cross-section is reduced and the winding turns are fewer
- Bthe semiconductor devices in a switching power supply operate in the switching state, with high efficiency, so the heat sink becomes compact and lightweight
- Cthe working principle of a switching power supply is much simpler than that of a linear power supply, so the number of components in the equipment is greatly reduced
- Dthe PWM technique used in switching power supplies operates quietly without noise, needs no EMC measures, so the equipment size is reduced
Switchers are lighter because (1) the high switching frequency shrinks the transformer core and turn count (A), and (2) switching devices run efficiently so the heatsink is small (B). C is false (switchers have more parts), and D is false — PWM edges generate noise and EMC filtering is required, not omitted.
US–China difference: US hams also prefer switchers for field ops, but add ferrite chokes for RFI.
Common pitfall: Believing a switcher needs no EMC treatment — its harmonics are a classic noise source.
Real on-air practice: A lightweight 13.8 V switcher is great portable gear, but you may need a line filter to keep the band quiet.
将220V交流输入变换为13.8V直流输出的通信开关电源的一般工作过程是：
- A将交流输入整流滤波为高压直流，由半导体开关电路变成高压脉冲电流，由变压器变成低压脉冲，再整流滤波成为输出的低压直流
- B将交流输入整流滤波为高压直流，由变压器变成低压脉冲，由半导体开关电路变成低压直流，滤波后输出
- C由变压器将交流输入变为低压交流，由半导体开关电路变成超音频脉冲电流，经整流滤波为低压直流
- D由大功率半导体三极管将交流输入变为高压直流，由专用集成电路变成超音频脉冲电流，再经整流滤波成为输出的低压直流
The general working process of a communication switching power supply that converts 220 V AC input to 13.8 V DC output is:
- Arectify and filter the AC input into high-voltage DC, convert it via a semiconductor switching circuit into high-voltage pulse current, transform it via a transformer into low-voltage pulses, then rectify and filter into the low-voltage DC output
- Brectify and filter the AC input into high-voltage DC, transform it via a transformer into low-voltage pulses, convert it via a semiconductor switching circuit into low-voltage DC, then filter and output
- Cuse a transformer to convert the AC input into low-voltage AC, convert it via a semiconductor switching circuit into ultra-audio pulse current, then rectify and filter into low-voltage DC
- Duse a high-power semiconductor transistor to convert the AC input into high-voltage DC, convert it via a dedicated IC into ultra-audio pulse current, then rectify and filter into the low-voltage DC output
An off-line switcher rectifies AC→high-voltage DC, chops it with a switching circuit into HV pulses, uses a small high-frequency transformer to step down to LV pulses, then rectifies/filters to LV DC (A). B puts the transformer before chopping (wrong for off-line); C uses a bulky 50 Hz step-down transformer (that’s a linear supply); D misstates the chain.
US–China difference: The AC→HV DC→chop→HF transformer→LV rectify flow is standard in US switchers too.
Common pitfall: Thinking the step-down happens at 50 Hz with a big transformer (that’s linear, not switching).
Real on-air practice: Your 13.8 V switcher does exactly this chain to feed the rig.
有时，使用锁相环频率合成器的本机振荡器（LO）会为混频之后的信号增添相位噪声。可能的原因是：
- A从鉴相检测LO的频率漂移到滤波产生环路的校正电压需要一定时间。该时延造成本振信号中的宽带相位噪声不能得到充分抑制
- B锁相环路中的压控振荡器（VCO）多为宽带可调谐LC振荡器。相比石英晶体振荡器等窄带振荡器，其输出相位噪声会在本质上更大一些
- C有些频率合成器采用多次混频方案，多个VCO的相位噪声的叠加使输出信噪比下降
- D频率合成器中的数字分频电路在信号电平跳变时会产生谐波，并因此产生相位噪声
Sometimes a local oscillator (LO) using a PLL (phase-locked loop) frequency synthesizer adds phase noise to the signal after mixing. Possible reasons are: (Choose all that apply.)
- Ait takes some time from the phase detector detecting the LO’s frequency drift to the loop filter producing the correction voltage; this delay means the broadband phase noise in the local-oscillator signal cannot be fully suppressed
- Bthe VCO (voltage-controlled oscillator) in a PLL is usually a wideband tunable LC oscillator; compared with narrowband oscillators such as quartz crystal oscillators, its output phase noise is inherently larger
- Csome frequency synthesizers use a multiple-mixing scheme, and the superposition of several VCOs’ phase noise lowers the output signal-to-noise ratio
- Dthe digital frequency-divider circuit in the synthesizer produces harmonics when signal levels switch, thereby generating phase noise
PLL LO phase noise arises from: loop-filter delay limiting how fast drift is corrected (A), the VCO’s inherently higher noise versus a crystal reference (B), and multiple-VCO/multi-mix schemes summing noise (C). D describes harmonic/spurious generation by the divider, not the dominant phase-noise mechanism, so it is not selected.
US–China difference: PLL phase-noise sources are the same in US transceiver design.
Common pitfall: Attributing all synthesizer noise to the digital divider’s harmonics rather than the VCO/loop.
Real on-air practice: A clean reference and wide loop bandwidth keep your LO quiet for weak-signal work.
很多业余无线电收发信机都在本机振荡电路中使用了直接数字频率合成器（DDS）。它的主要特点是：
- A电路结构简洁，无锁相捕捉范围限制，相位噪声低，跳换频率速度快
- B采用同样等级的参考振荡器时频率稳定度优于锁相环频率合成器
- C与锁相环频率合成器相比，可以使用速度较低的数字逻辑器件
- D直接产生纯净的正弦波信号，无需任何形式的滤波
Many amateur transceivers use a direct digital frequency synthesizer (DDS) in their local-oscillator circuit. Its main characteristics are:
- Asimple circuit structure, no PLL capture-range limit, low phase noise, fast frequency switching
- Bwith the same grade of reference oscillator, its frequency stability is better than a PLL frequency synthesizer
- Ccompared with a PLL frequency synthesizer, it can use lower-speed digital logic devices
- Dit directly produces a pure sine-wave signal without any filtering
DDS offers a simple architecture, no capture-range limit, low phase noise, and very fast hopping (A). Its stability tracks the reference (not better than PLL per se, B false), it needs fast logic (C false), and its output contains images/spurs requiring an anti-alias filter (D false).
US–China difference: DDS chips (e.g., AD9850) are popular in US homebrew rigs too.
Common pitfall: Assuming DDS output is a clean sine needing no filtering — it has Nyquist images.
Real on-air practice: A DDS VFO lets you step frequency in 1 Hz increments instantly.
电阻是无源元件，为什么也会产生噪声？
- A电路元件都会产生热噪声，大小与其阻值和温度高低有关
- B电阻的制造工艺不过关
- C金属膜电阻绝无噪声
- D音频电路中的电阻噪声最小，尤其是在贴近直流的频段中
A resistor is a passive component, so why does it also produce noise?
- Aall circuit components generate thermal noise, whose magnitude relates to their resistance value and temperature
- Bthe resistor’s manufacturing process is substandard
- Cmetal-film resistors are absolutely noise-free
- Dresistors in audio circuits have the least noise, especially near DC
All resistive elements exhibit Johnson–Nyquist thermal noise, proportional to resistance and absolute temperature (A). It is fundamental, not a manufacturing defect (B false); no resistor is noise-free (C false); near DC thermal noise is flat, not minimal (D false).
US–China difference: Thermal noise physics is the same in US electronics.
Common pitfall: Believing metal-film resistors are silent — they still have thermal noise.
Real on-air practice: A low-noise receive preamp uses small resistances to keep thermal noise down.
有源器件的噪声主要包括：
- A散粒噪声
- B散弹噪声
- C热噪声
- D开关噪声
The noise of active devices mainly includes: (Choose all that apply.)
- Ashot noise (散粒噪声)
- Bshot noise (散弹噪声)
- Cthermal noise
- Dswitching noise
Active-device noise includes shot noise and thermal noise. Note that 散粒噪声 (A) and 散弹噪声 (B) are two written forms of the same term — shot noise — so both are marked correct, and C (thermal noise) is also correct. D (switching noise) is not a fundamental active-device noise type in this context.
US–China difference: Shot and thermal noise are universal active-device noise mechanisms.
Common pitfall: Treating 散粒噪声 and 散弹噪声 as two different noises — they are the same concept spelled differently.
Real on-air practice: A low-noise amplifier’s NF is set by these fundamental noises plus its own design.
为什么过长的同轴电缆或是VSWR过高的同轴电缆都为收信机增添噪声？
- A电缆过长或VSWR过高均增加欧姆损耗，增添热噪声
- B电缆过长易感生静电，产生QRN
- CVSWR过高则电缆外皮带电，干扰周边设备引发噪声
- D此命题不成立。VSWR与损耗不相干
Why do an overly long coaxial cable, or a coaxial cable with too high a VSWR (standing-wave ratio), add noise to a receiver?
- Aboth excessive cable length and high VSWR increase ohmic loss, adding thermal noise
- Ban overly long cable easily induces static electricity, producing QRN
- Chigh VSWR makes the cable’s outer shield carry charge, interfering with nearby equipment and causing noise
- Dthis proposition does not hold; VSWR is unrelated to loss
A long feed line or a high SWR (驻波比 / VSWR) raises ohmic loss; that loss adds its own thermal noise and raises the system noise figure, degrading the receiver (A). B/C describe unrelated electrostatic effects; D is false — VSWR does increase loss.
US–China difference: Same feed-line noise-figure effect taught in US antenna/transmission-line theory.
Common pitfall: Thinking VSWR only risks damaging the transmitter and ignoring its noise-figure penalty on receive.
Real on-air practice: A 30 m lossy coax on 432 MHz can bury weak EME echoes in thermal noise.
为什么大气也有噪声？
- A大气噪声与大气放电有关，亦称天电噪声，简称QRN
- BQRN的一般分布是随着频率的升高而逐渐增强的
- C大气将无线电波相互混频，继而产生QRM和啁啾声
- D大气是一种等离子体，是有热噪声的
Why does the atmosphere also have noise?
- Aatmospheric noise is related to atmospheric discharges, also called static noise, abbreviated QRN
- BQRN generally increases as frequency rises
- Cthe atmosphere mixes radio waves with each other, thereby producing QRM and chirps
- Dthe atmosphere is a plasma and has thermal noise
Atmospheric (static) noise — 天电噪声, abbreviated QRN — comes from lightning and other atmospheric electrical discharges (A). QRN actually decreases with frequency (B false); mixing/QRM (C) is man-made interference, not atmosphere; D misstates the mechanism.
US–China difference: QRN (static) is the same phenomenon US hams battle, especially on HF.
Common pitfall: Thinking QRN gets worse at higher frequencies — it is strongest on low bands and fades by VHF/UHF.
Real on-air practice: Summer thunderstorms send QRN crashing across your 40 m receiver.
劣质开关电源会为无线电接收机增添电磁噪声。源头主要是：
- A开关电源中的开关电路的谐波辐射
- B工频电源变压器的漏磁感应
- C开关电源中的整流电路的滤波电容容量不足
- D元器件的安装过于粗糙，打火、拉弧带来电磁干扰
A poor-quality switching power supply adds electromagnetic noise to a radio receiver. The main source is:
- Aharmonic radiation from the switching circuit in the switching power supply
- Bleakage magnetic induction from the power-frequency power transformer
- Cinsufficient filter-capacitance in the rectifier circuit of the switching power supply
- Doverly crude component mounting, causing arcing and sparking that brings electromagnetic interference
The dominant noise from a bad switcher is the harmonic radiation of its switching circuit (conducted and radiated), which spreads across the bands (A). B is a linear-supply (50 Hz transformer) issue; C causes ripple, not broadband RFI; D is incidental arcing, not the main source.
US–China difference: Cheap switchers are a top noise complaint for US hams too; ferrite chokes help.
Common pitfall: Blaming the 50 Hz transformer (linear-supply artifact) for a switcher’s noise.
Real on-air practice: A noisy wall-wart switcher can blanket your 2 m receiver with birdies.
💬 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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