CRAC Class B (2025) — Questions 1071–1080

U1138. The output signal voltage of a circuit is half the input signal voltage. The gain of this circuit is approximately:

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：

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Voltage gain = 20·log₁₀(0.5) ≈ −6.02 ≈ −6 dB. (Half voltage, not half power; the −3 dB is the power version.)

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.