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FCC E4C - 业余电台实践与测试

FCC 题库总览 > E级 (最高特级 Extra) > E4 业余电台实践与测试 > E4C

小节 E4C：业余电台实践与测试

本小节共包含 14 道中英双语精校考题
#E4C01🔗
What is an effect of excessive phase noise in an SDR receiver’s master clock oscillator?
SDR 接收器主时钟振荡器中相位噪声过多会产生什么影响？
A
It limits the receiver’s ability to receive strong signals
它限制了接收器接收强信号的能力
B
It can affect the receiver’s frequency calibration
它会影响接收机的频率校准
C
It decreases the receiver’s third-order intercept point
它降低了接收器的三阶截点
D
It can combine with strong signals on nearby frequencies to generate interference
它可以与附近频率上的强信号结合产生干扰
✓ 正确答案
#E4C02🔗
Which of the following receiver circuits can be effective in eliminating interference from strong out-of-band signals?
以下哪种接收电路可以有效消除强带外信号的干扰？
A
A front-end filter or preselector
前端过滤器或预选器
✓ 正确答案
B
A narrow IF filter
窄中频滤波器
C
A notch filter
陷波滤波器
D
A properly adjusted product detector
正确调整的产品检测器
#E4C03🔗
What is the term for the suppression in an FM receiver of one signal by another stronger signal on the same frequency?
调频接收器中一个信号被同一频率上的另一个更强信号抑制的术语是什么？
A
Desensitization
脱敏
B
Cross-modulation interference
交叉调制干扰
C
Capture effect
捕捉效果
✓ 正确答案
D
Frequency discrimination
频率歧视
#E4C04🔗
What is the noise figure of a receiver?
接收机的噪声系数是多少？
A
The ratio of atmospheric noise to phase noise
大气噪声与相位噪声之比
B
The ratio of the noise bandwidth in hertz to the theoretical bandwidth of a resistive network
电阻网络的噪声带宽（以赫兹为单位）与理论带宽之比
C
The ratio in dB of the noise generated in the receiver to atmospheric noise
接收器中产生的噪声与大气噪声的比率（以 dB 为单位）
D
The ratio in dB of the noise generated by the receiver to the theoretical minimum noise
接收器产生的噪声与理论最小噪声的比率（以 dB 为单位）
✓ 正确答案
#E4C05🔗
What does a receiver noise floor of -174 dBm represent?
-174 dBm 的接收机本底噪声代表什么？
A
The receiver noise is 6 dB above the theoretical minimum
接收器噪声比理论最小值高 6 dB
B
The theoretical noise in a 1 Hz bandwidth at the input of a perfect receiver at room temperature
室温下完美接收器输入端 1 Hz 带宽内的理论噪声
✓ 正确答案
C
The noise figure of a 1 Hz bandwidth receiver
1 Hz 带宽接收器的噪声系数
D
The receiver noise is 3 dB above theoretical minimum
接收器噪声比理论最小值高 3 dB
#E4C06🔗
How much does increasing a receiver’s bandwidth from 50 Hz to 1,000 Hz increase the receiver’s noise floor?
将接收器的带宽从 50 Hz 增加到 1,000 Hz 会使接收器的本底噪声增加多少？
A
3 dB
3分贝
B
5 dB
5分贝
C
10 dB
10分贝
D
13 dB
13分贝
✓ 正确答案
#E4C07🔗
What does the MDS of a receiver represent?
接收者的MDS代表什么？
A
The meter display sensitivity
仪表显示灵敏度
B
The minimum discernible signal
最小可辨别信号
✓ 正确答案
C
The modulation distortion specification
调制失真规范
D
The maximum detectable spectrum
最大可检测光谱
#E4C08🔗
An SDR receiver is overloaded when input signals exceed what level?
当输入信号超过什么电平时，SDR 接收器就会过载？
A
One-half of the maximum sample rate
最大采样率的二分之一
B
One-half of the maximum sampling buffer size
最大采样缓冲区大小的二分之一
C
The maximum count value of the analog-to-digital converter
模数转换器最大计数值
D
The reference voltage of the analog-to-digital converter
模数转换器的参考电压
✓ 正确答案
#E4C09🔗
Which of the following choices is a good reason for selecting a high IF for a superheterodyne HF or VHF communications receiver?
以下哪项选择是为超外差 HF 或 VHF 通信接收机选择高 IF 的充分理由？
A
Fewer components in the receiver
接收器中的元件更少
B
Reduced drift
减少漂移
C
Easier for front-end circuitry to eliminate image responses
前端电路更容易消除图像响应
✓ 正确答案
D
Improved receiver noise figure
改进的接收器噪声系数
#E4C10🔗
What is an advantage of having a variety of receiver bandwidths from which to select?
有多种接收器带宽可供选择有什么好处？
A
The noise figure of the RF amplifier can be adjusted to match the modulation type, thus increasing receiver sensitivity
可以调整射频放大器的噪声系数以匹配调制类型，从而提高接收器灵敏度
B
Receiver power consumption can be reduced when wider bandwidth is not required
当不需要更宽的带宽时，可以降低接收器功耗
C
Receive bandwidth can be set to match the modulation bandwidth, maximizing signal -to-noise ratio and minimizing interference
接收带宽可设置为与调制带宽相匹配，从而最大化信噪比并最小化干扰
✓ 正确答案
D
Multiple frequencies can be received simultaneously if desired
如果需要，可以同时接收多个频率
#E4C11🔗
Why does input attenuation reduce receiver overload on the lower frequency HF bands with little or no impact on signal-to-noise ratio?
为什么输入衰减可以减少低频 HF 频段上的接收机过载，而对信噪比影响很小或没有影响？
A
The attenuator has a low-pass filter to increase the strength of lower frequency signals
衰减器具有低通滤波器，可增加低频信号的强度
B
The attenuator has a noise filter to suppress interference
衰减器带有噪声滤波器，可抑制干扰
C
Signals are attenuated separately from the noise
信号与噪声分开衰减
D
Atmospheric noise is generally greater than internally generated noise even after attenuation
即使在衰减后，大气噪声通常也大于内部产生的噪声
✓ 正确答案
#E4C12🔗
How does a narrow-band roofing filter affect receiver performance?
窄带修平滤波器如何影响接收器性能？
A
It improves sensitivity by reducing front-end noise
它通过降低前端噪声来提高灵敏度
B
It improves intelligibility by using low Q circuitry to reduce ringing
它通过使用低 Q 电路减少振铃来提高清晰度
C
It improves blocking dynamic range by attenuating strong signals near the receive frequency
它通过衰减接收频率附近的强信号来提高阻塞动态范围
✓ 正确答案
D
All these choices are correct
所有这些选项都是正确的
#E4C13🔗
What is reciprocal mixing?
什么是相互混合？
A
Two out-of-band signals mixing to generate an in-band spurious signal
两个带外信号混合以生成带内杂散信号
B
In-phase signals cancelling in a mixer resulting in loss of receiver sensitivity
混频器中的同相信号抵消导致接收器灵敏度损失
C
Two digital signals combining from alternate time slots
来自交替时隙的两个数字信号组合
D
Local oscillator phase noise mixing with adjacent strong signals to create interference to desired signals
本地振荡器相位噪声与相邻强信号混合，对所需信号产生干扰
✓ 正确答案
#E4C14🔗
What is the purpose of the receiver IF Shift control?
接收器 IF Shift 控制的目的是什么？
A
To permit listening on a different frequency from the transmitting frequency
允许在与发射频率不同的频率上收听
B
To change frequency rapidly
快速改变频率
C
To reduce interference from stations transmitting on adjacent frequencies
减少相邻频率发射站的干扰
✓ 正确答案
D
To tune in stations slightly off frequency without changing the transmit frequency
在不改变发射频率的情况下调谐稍微偏离频率的电台
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