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 Measurement and Instruments with 47 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.
用万用表的直流电压档测量正负对称的方波电压（占空比为1:1）。所得读数为：
- A零值
- B该电压的最大值
- C该电压最大值的1/2
- D该电压最大值的2倍
A multimeter’s DC voltage range is used to measure a bipolar symmetric square-wave voltage (duty cycle 1:1). The reading obtained is:
- Azero
- Bthe maximum value of the voltage
- Cone-half of the maximum value of the voltage
- Dtwice the maximum value of the voltage
A DC voltmeter reads the average (mean) value. A bipolar symmetric square wave that spends equal time at +V and −V has an average of zero, so the reading is zero (A).
US–China difference: Same principle; a DC meter shows the average, which is zero for a symmetric square wave.
Common pitfall: Expecting the peak value; the DC range does not show peaks of an AC-like waveform.
Real on-air practice: Measuring a keyed CW waveform’s DC component with a DC meter gives the average, not the swing.
如果用磁电式万用表的交流电压档测量正负对称的方波电压（占空比为1:1），其指针所示的电压读数：
- A大于该电压的峰值
- B为该电压的峰值
- C为该电压的峰-峰值
- D为该电压的平均值
If a moving-coil (magneto-electric) multimeter’s AC voltage range is used to measure a bipolar symmetric square-wave voltage (duty cycle 1:1), the voltage reading shown by its pointer:
- Ais greater than the peak value of the voltage
- Bis the peak value of the voltage
- Cis the peak-to-peak value of the voltage
- Dis the average value of the voltage
A moving-coil AC meter rectifies the waveform and is calibrated to read the RMS value of a sine wave (using the sine form factor ≈1.11). A square wave has a rectified average equal to its peak (Vpk); multiplying by 1.11 yields about 1.11·Vpk, which exceeds the peak (A). It is neither the peak (B), peak-to-peak (C), nor the average (D).
US–China difference: Analog VOMs in the US have the same sine-calibrated AC scale, so non-sine readings are inaccurate.
Common pitfall: Assuming an AC range reads true RMS; on a square wave it over-reads versus the peak.
Real on-air practice: Measuring a square-wave/keyed signal with an old analog meter gives misleading AC volts.
用指针式万用表的直流电压档测量最小值为0的方波电压（占空比为1:1），得到的读数是该电压的：
- A峰值的1/2，亦为有效值
- B零值
- C峰值
- D峰-峰值
Using an analog (pointer) multimeter’s DC voltage range to measure a square-wave voltage whose minimum value is 0 (duty cycle 1:1), the reading obtained is which value of the voltage:
- Aone-half of the peak value, which is also the RMS value
- Bzero
- Cthe peak value
- Dthe peak-to-peak value
A 0-to-Vpk square wave at 50% duty has an average = Vpk/2. A DC meter reads this average. For this waveform the RMS value also equals Vpk/2 (since RMS² = (Vpk²·0.5 + 0²·0.5) = Vpk²/2). So the reading is half the peak and equals the RMS value (A).
US–China difference: Same averaging behavior of analog DC meters in the US.
Common pitfall: Reading the peak or peak-to-peak; the DC range shows the mean, here Vpk/2.
Real on-air practice: A 50% key-down/key-up DC voltage across a load reads half the supply — matching this result.
用万用表的电阻档测量一个电路。最开始，电表指示电路的阻值很小。但是随着测量时间的延长，测量值却变得越来越大。这是因为：
- A这个电路两端可能存在一个很大的电容
- B万用表出了故障
- C这个电路两端可能存在一个很大的电感
- D这个电路中存在一个周期性的交流电压
A multimeter’s resistance range is used to measure a circuit. At first the meter indicates a very small resistance for the circuit, but as the measurement time lengthens the reading becomes increasingly large. This is because:
- AThere may be a very large capacitor across this circuit
- BThe multimeter is faulty
- CThere may be a very large inductor across this circuit
- DThere is a periodic AC voltage in this circuit
An ohmmeter supplies a small current to measure resistance. If a large capacitor is across the circuit, it initially acts like a short (low reading) while charging, then its impedance rises as it fills, so the reading climbs toward infinity (A). A large inductor would instead show a rising-then-settling or initially high reading, not this pattern; an AC source or fault (C/D/B) does not explain the gradual rise.
US–China difference: Ohmmeter behavior with capacitors is the same physics everywhere.
Common pitfall: Assuming the meter is broken; in-circuit capacitor charging is the usual cause.
Real on-air practice: Measuring a circuit with a big filter cap across it shows exactly this climbing resistance.
测量一个电解电容器是否完好应当使用：
- A指针式万用表的电阻档
- B数字万用表的电容测试档（如果仪表具备该功能）
- C任意一种万用表的电流档
- D蓄电池充电器并配合进行短路放电实验
To check whether an electrolytic capacitor is sound, one should use: (Choose all that apply.)
- Athe resistance range of an analog (pointer) multimeter
- Bthe capacitance test range of a digital multimeter (if the instrument has this function)
- Cthe current range of any multimeter
- Da battery charger together with a short-circuit discharge test
A sound electrolytic capacitor can be checked with an analog ohmmeter (it should show a charging swing to high resistance, A) and, more directly, with a digital multimeter’s capacitance function if available (B). A current range (C) is unsuitable, and a charger plus short-circuit test (D) is dangerous and not a proper test.
US–China difference: Same test methods used by US hams; DMM capacitance mode is the modern preferred check.
Common pitfall: Trying to measure capacitance on a current range, or shorting a charged cap to “test” it.
Real on-air practice: A DMM capacitance mode quickly confirms a dried-up electrolytic in a power supply.
用指针式万用电表的电阻档测量一个常用元件，表笔第一次连接时表针挥动了一下，但很快回到零点。断开表笔重新连接，表针却不再有任何指示。正确的推论是：
- A该元件可能是一个电解电容器
- B该元件肯定是一支损坏了的电阻
- C万用表的准确度肯定有问题
- D万用表的电池肯定电量不足了
Using an analog multimeter’s resistance range to measure a common component, the first time the test leads are connected the pointer flicks and then quickly returns to zero; after disconnecting and reconnecting the leads, the pointer shows no indication at all. The correct inference is:
- AThe component may be an electrolytic capacitor
- BThe component is definitely a damaged resistor
- CThe multimeter’s accuracy is definitely at fault
- DThe multimeter’s battery is definitely low
The behavior — an initial charging deflection on first connection, then settling, and little or no movement on a repeat connection (the component having retained charge) — is consistent with an electrolytic capacitor measured on an ohmmeter (A). The other options make absolute (“肯定/definitely”) claims that are not supported and are incorrect as the intended answer.
US–China difference: The ohmmeter “capacitor twitch” test is a classic US ham troubleshooting trick too.
Common pitfall: Over-committing to “definitely” conclusions (B/C/D) when the symptom only suggests a capacitor.
Real on-air practice: Reversing the leads on a good electrolytic gives another twitch — a quick in-shack go/no-go test.
指针式万用表的电压档有个“欧姆/伏（每伏欧姆）”指标。越大的每伏欧姆数越说明：
- A测量电压时电表对电路工作状态的影响小
- B测量电压时电表对电路工作状态的影响大
- C可以耐受的电压过载能力强
- D可以耐受的电压过载能力弱
An analog multimeter’s voltage range has an “ohms-per-volt” (ohms per volt) specification. A larger ohms-per-volt figure indicates that:
- Athe meter has less effect on the circuit’s operating state when measuring voltage
- Bthe meter has more effect on the circuit’s operating state when measuring voltage
- Cthe voltage overload withstand capability is strong
- Dthe voltage overload withstand capability is weak
Ohms-per-volt = the meter’s input resistance per volt of range; a higher figure means higher input resistance, so the meter draws less current and disturbs the circuit less while measuring voltage (A). Lower ohms/volt means more loading (B wrong); it does not describe overload strength (C/D wrong).
US–China difference: US analog VOMs are also spec’d in ohms/volt; higher is better (less loading).
Common pitfall: Thinking a high ohms/volt means stronger overload protection; it means higher input impedance.
Real on-air practice: A 20 kΩ/V meter on a high-impedance circuit loads it badly; a 100 kΩ/V FET meter is far gentler.
用数字万用表的直流电压档测量电路两点间某个等幅音频信号的电压，发现读数不为零。交换两支表笔之后再测，所得读数的极性反转。正确的推论是：
- A音频信号上叠加有直流成分
- B音频信号含有丰富的谐波
- C万用表的频率响应太差
- D表笔导线间的分布电容影响了测量
Using a digital multimeter’s DC voltage range to measure the voltage of a constant-amplitude audio signal between two points in a circuit, it is found that the reading is not zero. After swapping the two test leads and measuring again, the polarity of the reading reverses. The correct inference is:
- AA DC component is superimposed on the audio signal
- BThe audio signal is rich in harmonics
- CThe multimeter’s frequency response is too poor
- DThe distributed capacitance between the test-lead wires affected the measurement
A pure AC/audio signal has zero average, so a DC voltmeter would read zero and swapping leads would not change a zero reading. A non-zero reading that flips polarity when the leads are swapped proves a DC offset (a DC component) is present on top of the audio (A). Harmonics, bandwidth, or lead capacitance would not produce this polarity-reversing DC reading.
US–China difference: Same DC-meter behavior; a polarity-flipping non-zero DC reading implies a DC bias.
Common pitfall: Blaming meter bandwidth; the key clue is the polarity reversal on lead swap.
Real on-air practice: Measuring a microphone amp and seeing a flipped DC offset reveals a biased (keying/idle) stage.
下列几种图表中，最容易用来表达和解释PSK调制原理的是：
- A相位矢量图
- B波形图
- C频谱图
- D频谱瀑布图
Among the following charts, the one most easily used to express and explain the principle of PSK modulation is:
- Aphase vector diagram (constellation diagram)
- Bwaveform diagram
- Cspectrum diagram
- Dspectrum waterfall diagram
PSK (phase-shift keying, 相移键控) encodes data by changing the carrier phase, so a phase vector diagram / constellation (相位矢量图) most directly shows the discrete phase states. Waveform/spectrum plots are less intuitive for phase states.
US–China difference: Same — PSK is explained with constellation diagrams in both regions.
Common pitfall: Picking the waveform diagram; phase shifts are clearer on a vector/constellation plot.
Real on-air practice: PSK31/FT8 decoders display a constellation of phase points.
下列几种图表中，最容易用来表达和解释模拟FM调制原理的是：
- A频谱图
- B波形图
- C相位矢量图
- D星座图和眼图
Among the following charts, the one most easily used to express and explain the principle of analog FM modulation is:
- Aspectrum diagram
- Bwaveform diagram
- Cphase vector diagram
- Dconstellation diagram and eye diagram
Per the official answer key, a spectrum diagram (频谱图) is taken as the chart that most readily expresses and explains analog FM (频率调制) — it shows how the instantaneous frequency deviation spreads the signal into sidebands around the carrier. (Note: a time-domain waveform can also illustrate FM, but the key marks the spectrum as the intended answer.)
US–China difference: FM sideband structure (Bessel functions) is taught the same way; US hams see it on a spectrum display.
Common pitfall: Over-thinking whether waveform or spectrum is “better”; follow the key — spectrum.
Real on-air practice: On 2 m FM your signal occupies a few kHz of spectrum around the carrier.
下列几种图表中，最容易用来表达和解释SSB调制原理的是：
- A频谱图
- B波形图
- C相位矢量图
- D频谱瀑布图
Among the following charts, the one most easily used to express and explain the principle of SSB modulation is:
- Aspectrum diagram
- Bwaveform diagram
- Cphase vector diagram
- Dspectrum waterfall diagram
SSB (single sideband, 单边带) is best shown on a spectrum diagram (频谱图): it visibly demonstrates that the carrier is suppressed and only one sideband is transmitted, compared with the double-sideband AM spectrum.
US–China difference: Same — SSB spectrum (one sideband, no carrier) is universal.
Common pitfall: Picking the waveform; the sideband/carrier structure is a frequency-domain concept.
Real on-air practice: On 20 m USB you transmit only the upper sideband — a clean single lobe on the spectrum.
下列几种图表中，最容易用来表达和解释RTTY调制原理的是：
- A频率-时间曲线
- B功率-时间曲线
- C波形图
- D相位矢量图
Among the following charts, the one most easily used to express and explain the principle of RTTY modulation is:
- Afrequency-time curve
- Bpower-time curve
- Cwaveform diagram
- Dphase vector diagram
RTTY (radioteletype, 无线电传) uses frequency-shift keying (FSK) — two tones shifting with the mark/space bits. A frequency–time curve (频率-时间曲线) most directly shows the frequency switching between the two states.
US–China difference: RTTY FSK (e.g., 170 Hz shift) is the same worldwide.
Common pitfall: Picking a power–time curve; RTTY varies frequency, not amplitude.
Real on-air practice: You’ll see RTTY as two steady tones jumping back and forth on a waterfall.
下列几种图表中，最容易用来表达和解释SSTV调制原理的是：
- A频率-时间曲线
- B功率-时间曲线
- C波形图
- D相位矢量图
Among the following charts, the one most easily used to express and explain the principle of SSTV modulation is:
- Afrequency-time curve
- Bpower-time curve
- Cwaveform diagram
- Dphase vector diagram
SSTV (slow-scan television, 慢扫描电视) encodes each scan line as a tone whose frequency varies with the video brightness — a frequency-modulated audio sub-signal. A frequency–time curve (频率-时间曲线) best shows how brightness maps to frequency over time.
US–China difference: SSTV (e.g., Robot 36) uses FM audio tones the same way globally.
Common pitfall: Choosing a power–time curve; SSTV modulates frequency with picture content.
Real on-air practice: A received SSTV line appears as a rising/falling tone sweep on a frequency–time plot.
下列几种图表中，最容易用来表达和解释A、B、C类放大器工作点的差别的是：
- A波形图
- B频谱图
- C相位矢量图
- D频谱瀑布图
Among the following charts, the one most easily used to express and explain the difference in operating points of Class A, B, and C amplifiers is:
- Awaveform diagram
- Bspectrum diagram
- Cphase vector diagram
- Dspectrum waterfall diagram
Class A/B/C differ by conduction angle (360° / 180° / <180°). A waveform diagram (波形图) most directly shows how much of the input cycle the output follows — the clearest way to contrast the three classes.
US–China difference: Same classes A/B/AB/C with the same conduction-angle meanings.
Common pitfall: Picking the spectrum; distortion/harmonics relate, but conduction angle is a time-domain concept.
Real on-air practice: A Class C final is efficient but highly distorted — only acceptable for CW/FM, not linear SSB.
下列几种图表中，最容易用来表达和解释LC振荡器温度漂移程度的是：
- A频谱瀑布图
- B频谱图
- C相位矢量图
- D波形图
Among the following charts, the one most easily used to express and explain the degree of temperature drift of an LC oscillator is:
- Aspectrum waterfall diagram
- Bspectrum diagram
- Cphase vector diagram
- Dwaveform diagram
Temperature drift is a slow change of frequency over time. A spectrum waterfall diagram (频谱瀑布图) plots frequency vs. time with intensity, so a drifting LC oscillator shows a slanted trace — the best visualization of drift magnitude.
US–China difference: Same — waterfalls are standard on SDR displays everywhere.
Common pitfall: Picking a single static spectrum; drift needs the time axis a waterfall provides.
Real on-air practice: On a cold morning your VFO may visibly drift on the waterfall until it warms up.
图示电路为业余无线电爱好者常用的简易场强表。各部件的作用分别为：
- AA-接收电波，C1、C2、L-谐振选频，VD-检波，C3-旁路滤波，M-指示
- BA-接收电波，C1、C2旁路滤波，L-升压，VD-放大，C3-隔直流，M-指示
- CA-整流，C1、C2-隔直流，L-放大，VD-滤波，C3-谐振，M-指示
- DA-接收电波，C1、C2高频旁路，L-放大，VD-开关，C3-耦合，M-指示 [F]LK0614.jpg
The illustrated circuit is a simple field-strength meter commonly used by amateur radio operators. The functions of the components are respectively:
- AA—receives radio waves; C1, C2, L—resonant frequency selection; VD—detection; C3—bypass filtering; M—indication
- BA—receives radio waves; C1, C2—bypass filtering; L—step-up; VD—amplification; C3—DC blocking; M—indication
- CA—rectification; C1, C2—DC blocking; L—amplification; VD—filtering; C3—resonance; M—indication
- DA—receives radio waves; C1, C2—high-frequency bypass; L—amplification; VD—switch; C3—coupling; M—indication [F]LK0614.jpg
In the classic diode field-strength meter, the antenna (A) picks up the wave, the L-C1-C2 tank performs resonant selection (谐振选频), the diode (VD) detects/demodulates (检波) the RF to DC, C3 bypass-filters the reading, and the meter (M) indicates. Option A matches this signal chain; B/C/D misassign amplification/rectification roles a passive diode circuit cannot perform.
US–China difference: Same simple diode-detector field-strength meter used by hams everywhere.
Common pitfall: Thinking the diode “amplifies” — a diode only detects; there is no gain stage here.
Real on-air practice: You wave this near your antenna to confirm it’s radiating.
用一副臂长约10cm的小偶极天线并联一个晶体二极管和直流微安表，做一个简单的射频场强表。关于选用硅二极管还是锗二极管，正确的考虑应当是：
- A锗、硅二极管的起始导通电压分别为0.3V和0.7V。选用锗二极管时场强表更为灵敏
- B所有二极管都具有同样的单向导电特性。采用锗、硅二极管的效果完全相同
- C硅二极管的反向击穿电压比较高。选用硅管可以延长仪表的使用寿命
- D无关锗或硅二极管，这种电路过于简单，无法工作
Using a small dipole antenna about 10 cm per arm in parallel with a crystal diode and a DC microammeter to make a simple RF field-strength meter. Regarding the choice of silicon versus germanium diode, the correct consideration should be:
- AGermanium and silicon diodes have forward turn-on voltages of about 0.3 V and 0.7 V respectively. When a germanium diode is chosen the field-strength meter is more sensitive
- BAll diodes have the same unilateral conductivity. The effect of using germanium or silicon diodes is exactly the same
- CSilicon diodes have a relatively high reverse breakdown voltage. Choosing a silicon diode extends the instrument’s service life
- DRegardless of germanium or silicon diodes, this circuit is too simple to work
A germanium diode’s lower forward voltage (~0.3 V) lets it begin conducting (detecting) at weaker RF fields than a silicon diode (~0.7 V), making the meter more sensitive. B is false (turn-on voltages differ); C’s reverse-breakdown point is irrelevant to sensitivity; D is false — the simple circuit works.
US–China difference: Same diode physics; germanium is favored in sensitive RF detectors globally.
Common pitfall: Assuming all diodes behave identically for detection.
Real on-air practice: Old Germanium diodes (e.g., 1N34A) are prized for crystal-set and field-strength use.
在使用网络分析仪或天线分析仪测量电缆和天线的时候，需要使用校准件，包括：
- A50欧姆假负载接头
- B开路接头
- C短路接头
- D0dBm参考振荡器
When using a network analyzer or antenna analyzer to measure cables and antennas, calibration standards are required, including: (Choose all that apply.)
- Aa 50-ohm dummy-load connector
- Ban open-circuit connector
- Ca short-circuit connector
- Da 0 dBm reference oscillator
Standard one-port VNA/antenna-analyzer calibration uses three standards: a load (50 Ω dummy load, 负载), an open (开路), and a short (短路). These define the measurement reference plane. A 0 dBm reference oscillator (D) is not a calibration standard for this purpose.
US–China difference: Same SOLT (short-open-load-thru) calibration concept worldwide.
Common pitfall: Forgetting the load standard; many think only open/short are needed.
Real on-air practice: You calibrate your analyzer with the short/open/load before checking your antenna’s SWR.
为自己的FM电台选择驻波比表应注意什么问题？
- A频率范围和功率量程
- B最好可以在低于-40摄氏度的环境里使用
- C最好可以在高于90摄氏度的环境里使用
- D适用于振幅恒定的FM信号
What should you pay attention to when choosing an SWR meter for your FM station?
- Afrequency range and power range
- Bpreferably usable in environments below -40 °C
- Cpreferably usable in environments above 90 °C
- Dsuitable for FM signals of constant amplitude
The practical criteria for an SWR meter (驻波比表) are that its frequency range and power range (频率范围和功率量程) cover your FM band and transmitter power. Extreme temperature ratings (B, C) are irrelevant for normal station use, and “constant-amplitude FM” (D) is not a meaningful selection criterion.
US–China difference: Same selection rule — match band and power.
Common pitfall: Over-specifying environmental temperature instead of electrical range.
Real on-air practice: A 2 m (144 MHz) 50 W FM rig needs an SWR meter rated for VHF and ≥50 W.
如果用驻波比表测量发射机的输出功率，你应将仪表装在哪里？
- A在发射机与馈线之间
- B在13.8V电源输出端和电源线之间
- C在电源线和电台的电源输入端之间
- D在馈线和天线的馈电点之间
If you use an SWR meter to measure the output power of a transmitter, where should you place the meter?
- Abetween the transmitter and the feed line
- Bbetween the 13.8 V power-supply output and the power cable
- Cbetween the power cable and the station’s power input
- Dat the feed point between the feed line and the antenna
To measure the transmitter’s output power (not the antenna system), the SWR/power meter must be in the RF path right at the transmitter output — between the transmitter and the feed line (发射机与馈线之间). Placing it at the antenna feed point (D) measures power delivered there (after feed-line loss); B/C are on the DC supply, which is wrong.
US–China difference: Same — “transmitter output” is measured at the rig’s RF port.
Common pitfall: Measuring at the antenna and calling it “transmitter output” (feed-line loss makes it lower).
Real on-air practice: Rig → SWR meter → feed line → antenna is the standard inline order.
一个放大器具有20dB的信号增益，其意义是：
- A放大器把相当于输入信号的100倍的能量从电源转移到了负载
- B放大器产生了相当于输入信号的100倍的能量并将之传向负载
- C放大器把输入信号的能量放大了100倍
- D放大器把输入信号的能量放大了99倍
An amplifier has a signal gain of 20 dB. This means:
- Athe amplifier transfers energy equivalent to 100 times the input signal from the power supply to the load
- Bthe amplifier generates energy equivalent to 100 times the input signal and delivers it to the load
- Cthe amplifier amplifies the input signal’s energy by 100 times
- Dthe amplifier amplifies the input signal’s energy by 99 times
20 dB power gain = 10^(20/10) = 100×. Crucially, an amplifier does not create energy from the input — it draws energy from the power supply and delivers 100× the input’s power to the load (A). B/C/D wrongly imply the input energy itself is “amplified/multiplied,” which violates energy conservation (the extra energy comes from the supply).
US–China difference: Same — gain is power from the supply, not creation of input energy.
Common pitfall: Thinking the amplifier multiplies the input’s own energy; it controls supply energy.
Real on-air practice: A 100 W PA with 1 W drive has 20 dB gain, drawing the other 99 W from its 13.8 V supply.
射频信号通过某电路时产生了20dB的损耗。这部分被损耗的能量：
- A被电路转化为其他形式的能量，比如发热耗散或以无线电波的形式辐射到了其他地方
- B在电路中消失了
- C返回了信号源
- D一部分在电路中消失了，另一部分返回了信号源
When an RF signal passes through a certain circuit, a loss of 20 dB is produced. This lost energy:
- Ais converted by the circuit into other forms of energy, such as dissipated as heat or radiated elsewhere in the form of radio waves
- Bdisappears within the circuit
- Creturns to the signal source
- Dpartly disappears within the circuit and partly returns to the signal source
By energy conservation, the 20 dB of lost power is not destroyed — it is transformed into heat (in resistances) or radiated away (leakage). B and D claim energy “disappears” (impossible); C says it returns to the source, which describes reflection, not dissipation loss.
US–China difference: Same physics — loss becomes heat/radiation.
Common pitfall: Believing dissipated energy vanishes rather than converting form.
Real on-air practice: A long feed line’s loss warms the cable and wastes your watts as heat.
某电路输出信号功率是输入信号功率的100倍。该电路的增益为：
- A20dB
- B10dB
- C100dB
- D1dB
The output signal power of a circuit is 100 times the input signal power. The gain of this circuit is:
- A20 dB
- B10 dB
- C100 dB
- D1 dB
Power gain in dB = 10·log₁₀(Pout/Pin) = 10·log₁₀(100) = 10×2 = 20 dB. Options B/C/D use wrong factors.
US–China difference: Same dB-power formula worldwide.
Common pitfall: Using 20·log (voltage formula) on a power ratio → would give 40 dB.
Real on-air practice: A 100 W amp driven by 1 W has 20 dB gain.
某电路输出信号功率是输入信号功率的100万倍。该电路的增益为：
- A60dB
- B100dB
- C99万dB
- D100万dB
The output signal power of a circuit is 1,000,000 times the input signal power. The gain of this circuit is:
- A60 dB
- B100 dB
- C990,000 dB
- D1,000,000 dB
10·log₁₀(10⁶) = 10×6 = 60 dB. Multiplying the ratio by 10⁶ adds 60 dB, not 100 dB or absurd million-dB values.
US–China difference: Same — each 10× in power is +10 dB.
Common pitfall: Treating the numeric ratio as dB directly (100万 → 100万 dB).
Real on-air practice: A receiver with 1,000,000× power gain from antenna to speaker is ~60 dB.
某电路输出信号功率是输入信号功率的5倍。该电路的增益约为：
- A7dB
- B3.5dB
- C5dB
- D14dB
The output signal power of a circuit is 5 times the input signal power. The gain of this circuit is approximately:
- A7 dB
- B3.5 dB
- C5 dB
- D14 dB
10·log₁₀(5) ≈ 10×0.699 = 6.99 ≈ 7 dB. B is half that (would be a voltage ratio misapplied); C confuses the ratio with dB; D uses 20·log.
US–China difference: Same approximation (5× ≈ 7 dB) used by hams everywhere.
Common pitfall: Using 20·log₁₀(5)≈14 dB, which is for voltage not power.
Real on-air practice: “A 5× power increase is about 7 dB” is a handy rule of thumb.
某电路输入信号功率是输出信号功率的一半。该电路的增益约为：
- A3dB
- B-3dB
- C0.5dB
- D-0.5dB
The input signal power of a circuit is half the output signal power. The gain of this circuit is approximately:
- A3 dB
- B-3 dB
- C0.5 dB
- D-0.5 dB
Input = ½ output means output = 2× input. Gain = 10·log₁₀(2) ≈ 3.01 ≈ 3 dB (positive — the circuit provides gain). B is the inverse (a 2× loss); C/D are far off.
US–China difference: Same — “doubling of power ≈ +3 dB” is universal.
Common pitfall: Reading the ratio backwards (input/output = ½) and answering −3 dB.
Real on-air practice: +3 dB = “twice the power” is the most-used conversion.
某电路输出信号电压是输入信号电压的100倍。该电路的增益为：
- A40dB
- B10dB
- C100dB
- D20dB
The output signal voltage of a circuit is 100 times the input signal voltage. The gain of this circuit is:
- A40 dB
- B10 dB
- C100 dB
- D20 dB
For a voltage ratio, gain in dB = 20·log₁₀(Vout/Vin) = 20·log₁₀(100) = 20×2 = 40 dB. B/C/D apply wrong factors (power formula or raw ratio).
US–China difference: Same — 20·log for voltage/current, 10·log for power.
Common pitfall: Using 10·log on a voltage ratio → 20 dB (option D).
Real on-air practice: A 100× voltage gain (e.g., RF preamp) is 40 dB.
某电路输出信号电压是输入信号电压的1万倍。该电路的增益为：（“x＾m”表示“x的m次方”）
- A80dB
- B10,000dB
- C9,999dB
- D10＾4dB
The output signal voltage of a circuit is 10,000 times the input signal voltage. The gain of this circuit is: (“x^m” means “x to the power m”)
- A80 dB
- B10,000 dB
- C9,999 dB
- D10^4 dB
Voltage gain = 20·log₁₀(10⁴) = 20×4 = 80 dB. Each factor of 10 in voltage is +20 dB, so 10⁴ → 80 dB. B/C/D wrongly treat the numeric value as dB.
US–China difference: Same logarithmic voltage-gain rule.
Common pitfall: Writing “10,000 dB” by confusing ratio with dB.
Real on-air practice: Cascaded 20 dB stages: four of them give 10⁴ voltage gain = 80 dB.
某电路输出信号电压是输入信号电压的10倍。该电路的增益约为：
- A20dB
- B7dB
- C14dB
- D15dB
The output signal voltage of a circuit is 10 times the input signal voltage. The gain of this circuit is approximately:
- A20 dB
- B7 dB
- C14 dB
- D15 dB
Voltage gain = 20·log₁₀(10) = 20 dB. (7 dB is the power equivalent of 5×; 14 dB would be 20·log₁₀(5).)
US–China difference: Same — “10× voltage = 20 dB” is universal.
Common pitfall: Mixing the 10×-voltage (20 dB) with the 5×-power (7 dB) rules.
Real on-air practice: A 10× RF voltage gain block is a 20 dB stage.
某电路输入信号电压是输出信号电压的一半。该电路的增益约为：
- A6dB
- B-6dB
- C-3dB
- D3dB
The input signal voltage of a circuit is half the output signal voltage. The gain of this circuit is approximately:
- A6 dB
- B-6 dB
- C-3 dB
- D3 dB
Input = ½ output ⇒ output = 2× input. Voltage gain = 20·log₁₀(2) ≈ 6.02 ≈ 6 dB (positive gain). B is the inverse; C/D are power-domain values.
US–China difference: Same — “voltage doubled ≈ +6 dB”.
Common pitfall: Using the power rule (+3 dB) for a voltage doubling.
Real on-air practice: +6 dB always means “twice the voltage / twice the SWR-reading amplitude”.
某电路输出信号功率是输入信号功率的1/100。该电路的增益为：
- A-20dB
- B-10dB
- C-100dB
- D100dB
The output signal power of a circuit is 1/100 of the input signal power. The gain of this circuit is:
- A-20 dB
- B-10 dB
- C-100 dB
- D100 dB
Gain = 10·log₁₀(1/100) = 10×(−2) = −20 dB (a 100× power attenuation). B/C/D misapply the sign or factor.
US–China difference: Same — attenuation is negative dB gain.
Common pitfall: Dropping the minus sign and answering +20 dB.
Real on-air practice: A 20 dB attenuator pad reduces power to 1/100.
某电路输出信号功率是输入信号功率的百万分之一。该电路的增益为：
- A-60dB
- B-100dB
- C990,000dB
- D-1,000,000dB
The output signal power of a circuit is one millionth of the input signal power. The gain of this circuit is:
- A-60 dB
- B-100 dB
- C990,000 dB
- D-1,000,000 dB
Gain = 10·log₁₀(10⁻⁶) = 10×(−6) = −60 dB. Each 10× power reduction is −10 dB, so 10⁶ → −60 dB. C/D are nonsensical literal conversions.
US–China difference: Same — 60 dB loss = one-millionth power.
Common pitfall: Writing “-1,000,000 dB” as if dB equals the raw fraction.
Real on-air practice: A 60 dB feed-line+filter isolation cuts a signal to a millionth.
某电路输出信号功率是输入信号功率的1/5。该电路的增益约为：
- A-7dB
- B3.5dB
- C-5dB
- D-14dB
The output signal power of a circuit is 1/5 of the input signal power. The gain of this circuit is approximately:
- A-7 dB
- B3.5 dB
- C-5 dB
- D-14 dB
Gain = 10·log₁₀(1/5) = −10·log₁₀(5) ≈ −6.99 ≈ −7 dB. (The +7 dB from U1125 is the inverse; here it’s a loss, so negative.)
US–China difference: Same rule.
Common pitfall: Forgetting the negative sign for an attenuation.
Real on-air practice: A 5× power drop (e.g., into a padding attenuator) is about −7 dB.
某电路输出信号功率是输入信号功率的一半。该电路的增益约为：
- A-3dB
- B3dB
- C0.5dB
- D-0.5dB
The output signal power of a circuit is half the input signal power. The gain of this circuit is approximately:
- A-3 dB
- B3 dB
- C0.5 dB
- D-0.5 dB
Gain = 10·log₁₀(0.5) ≈ −3.01 ≈ −3 dB. This is the famous “half power = −3 dB” relation. B is the inverse (a doubling).
US–China difference: Same — “−3 dB = half power” is universal.
Common pitfall: Answering +3 dB by misreading the direction of the ratio.
Real on-air practice: The −3 dB bandwidth of a filter is its “half-power” points.
某电路输出信号电压是输入信号电压的1/100。该电路的增益为：
- A-40dB
- B-10dB
- C-100dB
- D-20dB
The output signal voltage of a circuit is 1/100 of the input signal voltage. The gain of this circuit is:
- A-40 dB
- B-10 dB
- C-100 dB
- D-20 dB
Voltage gain = 20·log₁₀(1/100) = 20×(−2) = −40 dB. (Compare U1127: 100× → +40 dB; here it’s the inverse.)
US–China difference: Same — voltage attenuation uses 20·log.
Common pitfall: Using the power formula (−20 dB) on a voltage ratio.
Real on-air practice: A 40 dB voltage attenuator reduces amplitude to 1/100.
某电路输出信号电压是输入信号电压的万分之一。该电路的增益为：（“x＾m”表示“x的m次方”）
- A-80dB
- B-10,000dB
- C1/10,000dB
- D10＾-4dB
The output signal voltage of a circuit is one ten-thousandth of the input signal voltage. The gain of this circuit is: (“x^m” means “x to the power m”)
- A-80 dB
- B-10,000 dB
- C1/10,000 dB
- D10^-4 dB
Voltage gain = 20·log₁₀(10⁻⁴) = 20×(−4) = −80 dB. Each 10× voltage reduction is −20 dB, so 10⁻⁴ → −80 dB. B/C/D are wrong literal conversions.
US–China difference: Same logarithmic rule.
Common pitfall: Writing “-10,000 dB” instead of −80 dB.
Real on-air practice: Four 20 dB attenuator stages in series give 10⁻⁴ voltage = −80 dB.
某电路输出信号电压是输入信号电压的1/10。该电路的增益约为：
- A-20dB
- B-7dB
- C-14dB
- D0.143dB
The output signal voltage of a circuit is 1/10 of the input signal voltage. The gain of this circuit is approximately:
- A-20 dB
- B-7 dB
- C-14 dB
- D0.143 dB
Voltage gain = 20·log₁₀(1/10) = −20 dB. (The inverse of U1129.) B is the power-domain 5× loss value.
US–China difference: Same rule.
Common pitfall: Using 10·log (or the −7 dB power value) on a voltage ratio.
Real on-air practice: A 20 dB attenuator cuts voltage to 1/10.
某电路输出信号电压是输入信号电压的一半。该电路的增益约为：
- A-6dB
- B6dB
- C3dB
- D-3dB
The output signal voltage of a circuit is half the input signal voltage. The gain of this circuit is approximately:
- A-6 dB
- B6 dB
- C3 dB
- D-3 dB
Voltage gain = 20·log₁₀(0.5) ≈ −6.02 ≈ −6 dB. (Half voltage, not half power; the −3 dB is the power version.)
US–China difference: Same — “half voltage ≈ −6 dB”.
Common pitfall: Answering −3 dB (the power half-power value) for a voltage halving.
Real on-air practice: Cutting an audio signal’s amplitude in half is −6 dB.
若信号依次通过增益为x dB、y dB和z dB的三个电路，则总增益为：（“x＾m”表示“x的m次方”）
- A(x + y + z) dB
- B10＾((x + y + z) / 10) 倍
- C(x × y × z) dB
- D10＾((x × y × z) / 10) 倍
If a signal passes in sequence through three circuits with gains of x dB, y dB, and z dB, then the total gain is: (Choose all that apply.) (“x^m” means “x to the power m”)
- A(x + y + z) dB
- B10^((x + y + z) / 10) times
- C(x × y × z) dB
- D10^((x × y × z) / 10) times
Gains in dB add: total = (x + y + z) dB (A). Converting that sum back to a power ratio gives 10^((x+y+z)/10) (B). Multiplying the dB values (C) or raising 10 to their product (D) is dimensionally wrong.
US–China difference: Same — dB values are additive.
Common pitfall: Multiplying the dB numbers instead of adding them.
Real on-air practice: Preamp (+20 dB) + feed-line loss (−3 dB) + PA (+40 dB) = +57 dB total.
若信号通过增益为x dB的电路之后被功率分配器等分为两路，则每路增益为：（“x＾m”表示“x的m次方”）
- A(x – 3) dB
- B10＾((x – 3) / 10) 倍
- C(x / 2) dB
- D10＾((x / 2) / 10) 倍
If, after passing through a circuit with a gain of x dB, a signal is split equally into two paths by a power splitter, then the gain of each path is: (Choose all that apply.) (“x^m” means “x to the power m”)
- A(x – 3) dB
- B10^((x – 3) / 10) times
- C(x / 2) dB
- D10^((x / 2) / 10) times
An equal two-way power split divides power by 2, i.e., −3 dB per port. So each path’s gain is (x − 3) dB (A), and in power-ratio form 10^((x−3)/10) (B). Halving the dB number (C/D) is wrong — splitting power is −3 dB, not −x/2 dB.
US–China difference: Same — a 2-way split = 3 dB loss per port.
Common pitfall: Halving the dB value instead of subtracting 3 dB.
Real on-air practice: A 10 dB PA feeding a 2-way splitter gives ~7 dB at each antenna port.
接收机的信号强度表（S表）标有1至9的度盘分度，分度间隔为6dB。某电台以15W的功率发射时，S表读数为S9。现在，该电台减小功率并再次发射，S表的读数降至S4。该台的当前发射功率约为：
- A15mW
- B-18.2dBW
- C0.5W
- D-3dBW
A receiver’s signal-strength meter (S-meter) is graduated 1 to 9 with a 6 dB step per division. A station transmitting at 15 W gives an S-meter reading of S9. Now the station reduces power and transmits again, and the S-meter reading drops to S4. The station’s current transmit power is approximately: (Choose all that apply.)
- A15 mW
- B-18.2 dBW
- C0.5 W
- D-3 dBW
S9 → S4 is a drop of 5 divisions × 6 dB = 30 dB. 30 dB less power means a factor of 10^(−30/10) = 1/1000. 15 W / 1000 = 0.015 W = 15 mW (A). In dBW: 15 W = 10·log₁₀(15) ≈ 11.76 dBW; minus 30 dB = −18.2 dBW (B). C/D are far too high.
US–China difference: S-meter 6 dB/division is the same convention; S9 ≈ −73 dBm at the receiver is a worldwide reference.
Common pitfall: Miscalculating the number of divisions (S9 to S4 is 5, not 4) or dropping a sign.
Real on-air practice: Turning power down 30 dB is a common way to avoid overdriving a close-in station.
接收机的信号强度表（S表）标有1至9的度盘分度，分度间隔为6dB。某电台以100W的功率发射时，S表读数为S8。现在，该电台减小功率并再次发射时S表的读数降至S5。此时该台的发射功率约为：
- A1.58W
- B2dBW
- C5.56W
- D7.45dBW
A receiver’s signal-strength meter (S-meter) is graduated 1 to 9 with a 6 dB step per division. A station transmitting at 100 W gives an S-meter reading of S8. Now the station reduces power and transmits again, and the S-meter reading drops to S5. At this point the station’s transmit power is approximately: (Choose all that apply.)
- A1.58 W
- B2 dBW
- C5.56 W
- D7.45 dBW
S8 → S5 is a 3-division drop = 18 dB. Power factor = 10^(−18/10) ≈ 1/63.1. 100 W / 63.1 ≈ 1.58 W (A). In dBW: 100 W = 20 dBW; minus 18 dB = 2 dBW (B). C/D correspond to smaller drops and are wrong.
US–China difference: Same S-meter math.
Common pitfall: Using 4 divisions (S8→S5 is 3) or wrong dBW conversion.
Real on-air practice: QRP operators often cut from 100 W to ~1.5 W (about 18 dB) for nearby contacts.
功率为0dBm的射频信号通过增益为23dB的电路后，输出功率为：
- A23dBm
- B200mW
- C-7dBW
- D3.16V
An RF signal with a power of 0 dBm passes through a circuit with a gain of 23 dB; the output power is: (Choose all that apply.)
- A23 dBm
- B200 mW
- C-7 dBW
- D3.16 V
0 dBm + 23 dB = 23 dBm (A). 23 dBm = 10^(2.3) mW ≈ 199.5 ≈ 200 mW (B). In dBW: 23 − 30 = −7 dBW (C). D gives a voltage (3.16 V), which is not a power value (it depends on impedance), so it is not a valid output-power expression.
US–China difference: Same dBm/dBW conversions (0 dBm = 1 mW).
Common pitfall: Picking the voltage option D as if it were power; voltage ≠ power without impedance.
Real on-air practice: A 0 dBm (1 mW) measurement amp’d 23 dB becomes 200 mW — handy for drive-level checks.
功率为0dBμ的射频信号通过增益为36dB的电路后，输出功率为：
- A6dBm
- B4mW
- C-24dBW
- D447mV
An RF signal with a power of 0 dBμ passes through a circuit with a gain of 36 dB; the output power is: (Choose all that apply.)
- A6 dBm
- B4 mW
- C-24 dBW
- D447 mV
0 dBμ (dB relative to 1 µW) + 36 dB = 36 dBμ. Convert: dBm = dBμ − 30 = 6 dBm (A). 6 dBm = 10^0.6 mW ≈ 3.98 ≈ 4 mW (B). In dBW: 6 − 30 = −24 dBW (C). D is a voltage (447 mV), not a power, so it is not valid here.
US–China difference: Same — dBμ (dBµW) to dBm uses the −30 offset.
Common pitfall: Selecting the voltage figure as power; also mixing up dBμ with dBm start points.
Real on-air practice: Receiver sensitivity is sometimes quoted in dBμ; convert to dBm to compare with spec sheets.
功率为0dBW的射频信号通过增益为-36dB的电路后，输出功率为：
- A-6dBm
- B0.25mW
- C24dBμ
- D112mV
An RF signal with a power of 0 dBW passes through a circuit with a gain of −36 dB; the output power is: (Choose all that apply.)
- A-6 dBm
- B0.25 mW
- C24 dBμ
- D112 mV
0 dBW − 36 dB = −36 dBW. To dBm: −36 + 30 = −6 dBm (A). −6 dBm = 10^(−0.6) mW ≈ 0.251 ≈ 0.25 mW (B). To dBμ: −6 + 30 = 24 dBμ (C). D is a voltage (112 mV), not a power expression, so it is incorrect.
US–China difference: Same unit conversions (dBW↔dBm +30/−30; dBm↔dBμ likewise ±30).
Common pitfall: Choosing the voltage option; also sign errors when subtracting 36 dB.
Real on-air practice: A 0 dBW (1 W) signal attenuated 36 dB becomes 0.25 mW — e.g., through a long lossy feed line.
功率为-133dBm的射频信号通过增益为60dB的电路后，输出功率为：
- A-73dBm
- B-43dBμ
- C-103dBW
- D50μV
An RF signal with a power of −133 dBm passes through a circuit with a gain of 60 dB; the output power is: (Choose all that apply.)
- A-73 dBm
- B-43 dBμ
- C-103 dBW
- D50 μV
−133 dBm + 60 dB = −73 dBm (A). To dBμ: −73 + 30 = −43 dBμ (B). To dBW: −73 − 30 = −103 dBW (C). D is a voltage (50 µV), not a power, so it is not a valid output-power value here.
US–China difference: Same conversions; −73 dBm is near typical weak-signal levels.
Common pitfall: Mistaking the voltage option for power; watch the arithmetic (−133+60).
Real on-air practice: A faint −133 dBm satellite beacon amplified 60 dB by a preamp reaches a workable −73 dBm.
用示波器的交流耦合档测得电路中某个等幅音频信号的电压波形是正负对称的。现将输入耦合切换到直流档位，所得波形在垂直方向上发生了显著偏移。正确的推论是：
- A音频信号上叠加有直流成分
- B音频信号被示波器施加了直流偏置
- C示波器的频率响应太差
- D探头与地线间的分布电容影响了测量
Using an oscilloscope’s AC-coupling mode, the measured voltage waveform of an equal-amplitude audio signal in the circuit is symmetric about zero (positive and negative). Now, after switching the input coupling to the DC position, the resulting waveform shows a significant vertical shift. The correct inference is:
- Aa DC component is superimposed on the audio signal
- Bthe audio signal is given a DC bias by the oscilloscope
- Cthe oscilloscope’s frequency response is too poor
- Dthe distributed capacitance between the probe and the ground lead affected the measurement
示波器的交流耦合 (AC coupling) inserts a series capacitor that blocks any DC component, so the displayed waveform is centered on zero — which is why the equal-amplitude (等幅) audio signal appeared symmetric about positive and negative. When the coupling is switched to 直流档 (DC coupling), the DC path is restored and the trace shifts vertically by an amount equal to the DC offset. A significant vertical shift therefore means a DC component is present in the signal itself (A). B is wrong because the oscilloscope does not add a bias — it merely stops removing the existing one; C (poor frequency response) and D (probe-to-ground stray capacitance) would not cause a simple steady vertical offset between AC and DC coupling.
US–China difference: Identical principle on any oscilloscope (US or China); AC vs DC input coupling is a universal front-end feature.
Common pitfall: Blaming the shift on the oscilloscope adding a bias (option B); the scope only reveals the DC already there once AC blocking is removed.
Real on-air practice: When checking a transmitted FM or SSB audio line, a vertical shift in DC mode tells you the audio has a DC offset that could upset your modulator — a real alignment clue.
💬 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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