CRAC Class C (2025) — Questions 1191–1200
U1139. 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")
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”）
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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.
U1140. 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")
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”）
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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.
U1141. A receiver's signal-strength meter (S-meter) is graduated 1 to 9 with a 6 dB step per division.
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：
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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.
U1142. A receiver's signal-strength meter (S-meter) is graduated 1 to 9 with a 6 dB step per division.
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：
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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.
U1143. 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.)
功率为0dBm的射频信号通过增益为23dB的电路后，输出功率 为：
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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.
U1144. 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.)
功率为0dBμ的射频信号通过增益为36dB的电路后，输出功率 为：
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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.
U1145. 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.)
功率为0dBW的射频信号通过增益为-36dB的电路后，输出功 率为：
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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.
U1146. 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.)
功率为-133dBm的射频信号通过增益为60dB的电路后，输出 功率为：
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−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. 业余无线电台相关技术指标与知识 5 C H A P T E R Amateur-Station Technical Indicators and Related Knowledge 本章聚焦发射设备的国家技术指标要求与无线电设备相关标准。This chapter focuses on the national technical-indicator requirements for transmitting equipment and related radio-device standards. 发射设备技术指标 Transmitter Technical Indicators
U0638. The following indicators of amateur radio transmitting equipment must comply with relevant national regulations:
业余无线电发射设备的下列指标必须符合国家的相关规定：
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National rules for amateur transmitting equipment specifically mandate frequency tolerance (频率容限) and spurious-domain emission power (杂散域发射功率) limits (A). While out-of-band emission (C) is regulated generally, the exam's paired correct phrase is "frequency tolerance and spurious emission power"; modulation deviation/index (B) and allotted band/necessary bandwidth (D) are not the stated mandatory pair.
U0639. The radio transmitting equipment of an amateur station should meet the following principal technical indicators prescribed by the state:
业余电台的无线电发射设备应符国家规定的下列主要技术指 标：
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The required indicators are that the equipment meets the frequency tolerance and that its spurious emission stays within the maximum permissible power level (A). The distractors wrongly say spurious emission should be "not lower than" (i.e., allowed to exceed) the limit, which is the opposite of the rule.