FCC T3A - 无线电波特性与电波传播

#T3A01🔗

Why do VHF signal strengths sometimes vary greatly when the antenna is moved only a few feet?

为什么 VHF 信号强度有时会在天线仅移动几英尺时变化很大？

The signal path encounters different concentrations of water vapor

信号路径遇到不同浓度的水汽

VHF ionospheric propagation is very sensitive to path length

VHF 电离层传播对路径长度非常敏感

Multipath propagation cancels or reinforces signals

多径传播抵消或增强信号

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The Doppler effect causes slight frequency shifts which result in changes in signal strength

多普勒效应会导致轻微的频移，从而导致信号强度的变化

#T3A02🔗

How does vegetation affect UHF and microwave signals?

植被如何影响 UHF 和微波信号？

Causes knife-edge diffraction, distorting voice peaks

导致刀口衍射，扭曲语音峰值

Absorbs signals, leading to poor reception of weak signals

吸收信号，导致弱信号接收不良

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Amplifies signals, improving reception of weak signals

放大信号，改善微弱信号的接收

Has no effect

没有效果

#T3A03🔗

What antenna polarization is normally used for long-distance CW and SSB contacts on the VHF and UHF bands?

VHF 和 UHF 频段上的长距离 CW 和 SSB 联络通常使用什么天线极化？

Right-hand circular

右手圆形

Left-hand circular

左旋圆形

Horizontal

水平的

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Vertical

垂直的

#T3A04🔗

What is the effect of antenna cross-polarization over a line-of-sight VHF or UHF path?

天线交叉极化对视距 VHF 或 UHF 路径有何影响？

Modulation sidebands might become inverted

调制边带可能会反转

Received signal strength is reduced

接收信号强度降低_

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Signals have an echo effect

信号具有回声效应

Nothing significant will happen

没有什么重要的事情会发生

#T3A05🔗

When using a directional antenna, how might your station be able to communicate with a distant repeater if buildings or obstructions are blocking the direct line of sight path?

使用定向天线时，如果建筑物或障碍物阻挡了直接视线路径，您的站点如何与远处的中继器通信？

Change from vertical to horizontal polarization

从垂直极化变为水平极化

Try to find a path that reflects signals to the repeater

尝试找到将信号反射到中继器的路径

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Try the long path

尝试长路径

Increase the antenna SWR

增加天线驻波比

#T3A06🔗

What is the meaning of the term “picket fencing”?

“栅栏围栏”一词的含义是什么？

Alternating transmissions during a net operation

网络操作期间的交替传输

Rapid flutter on mobile signals due to multipath propagation

由于多径传播导致移动信号快速颤动

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A type of ground system used with vertical antennas

一种与垂直天线一起使用的地面系统

Interference from cable TV in the form of carriers at fixed intervals across the band

有线电视以固定间隔在频带内以载波形式产生的干扰

#T3A07🔗

What weather condition might decrease range at microwave frequencies?

什么天气条件可能会降低微波频率的范围？

High winds

大风

Low barometric pressure

低气压

Precipitation

降水量

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Colder temperatures

气温较低

#T3A08🔗

What is a likely cause of irregular fading of signals propagated by the ionosphere?

电离层传播的信号不规则衰落的可能原因是什么？

Frequency shift due to Faraday rotation

法拉第旋转引起的频移

Interference from thunderstorms

雷暴干扰

Intermodulation distortion

互调失真

Random combining of signals arriving via different paths

通过不同路径到达的信号的随机组合

✓ 正确答案

#T3A09🔗

Which of the following results from the fact that signals propagated by the ionosphere are elliptically polarized?

以下哪项是由电离层传播的信号呈椭圆偏振这一事实得出的？

Digital modes are unusable

数字模式无法使用

Either vertically or horizontally polarized antennas may be used for transmission or reception

垂直或水平极化天线均可用于发射或接收

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FM voice is unusable

FM语音无法使用

Both the transmitting and receiving antennas must be of the same polarization

发射天线和接收天线必须具有相同的极化

#T3A10🔗

What effect does multi-path propagation have on data transmissions?

多径传播对数据传输有何影响？

Transmission rates must be increased by a factor equal to the number of separate paths observed

传输速率必须增加一个等于观察到的单独路径数量的系数

Transmission rates must be decreased by a factor equal to the number of separate paths observed

传输速率必须降低等于观察到的单独路径数量的系数

No significant changes will occur if the signals are transmitted using FM

如果使用 FM 传输信号，不会发生重大变化

Error rates are likely to increase

错误率可能会增加

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#T3A11🔗

Which region of the atmosphere can reflect HF radio waves?

大气层的哪个区域可以反射高频无线电波？

The stratosphere

平流层

The troposphere

对流层

The ionosphere

电离层

✓ 正确答案

The electrosphere

电圈

#T3A12🔗

What effect does fog or rain have on 10-meter and 6-meter band signals?

雾或雨对10米和6米频段信号有什么影响？

Absorption

吸收

Little effect

影响不大

✓ 正确答案

Deflection

挠度

Increased range

增加射程

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FCC T3A - 无线电波特性与电波传播

小节 T3A：无线电波特性与电波传播