FCC E9D - 天线与传输线系统

#E9D01🔗

How much does the gain of an ideal parabolic reflector antenna increase when the operating frequency is doubled?

当工作频率加倍时，理想的抛物面反射面天线的增益会增加多少？

2 dB

2分贝

3 dB

3分贝

4 dB

4分贝

6 dB

6分贝

✓ 正确答案

#E9D02🔗

How can two linearly polarized Yagi antennas be used to produce circular polarization?

如何使用两个线极化八木天线产生圆极化？

Stack two Yagis to form an array with the respective elements in parallel planes fed 90 degrees out of phase

堆叠两个八木形成一个阵列，各个元件位于平行平面中，并以 90 度异相馈送

Stack two Yagis to form an array with the respective elements in parallel planes fed in phase

堆叠两个八木形成一个阵列，各个元件位于平行平面内同相馈电

Arrange two Yagis on the same axis and perpendicular to each other with the driven elements at the same point on the boom and fed 90 degrees out of phase

将两个八木器布置在同一轴上并相互垂直，从动元件位于动臂上的同一点，并以 90 度异相进给

✓ 正确答案

Arrange two Yagis collinear to each other with the driven elements fed 180 degrees out of phase

将两个八木器布置成彼此共线，驱动元件以 180 度异相馈送

#E9D03🔗

What is the most efficient location for a loading coil on an electrically short whip?

短电鞭上加载线圈最有效的位置是什么？

Near the center of the vertical radiator

靠近垂直散热器的中心

✓ 正确答案

As low as possible on the vertical radiator

垂直散热器上尽可能低

At a voltage maximum

在电压最大时

At a voltage null

在电压为零时

#E9D04🔗

Why should antenna loading coils have a high ratio of reactance to resistance?

为什么天线负载线圈应具有高电抗与电阻之比？

To swamp out harmonics

消除谐波

To lower the radiation angle

降低辐射角

To maximize efficiency

效率最大化

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To minimize the Q

最小化 Q

#E9D05🔗

Approximately how long is a Yagi’s driven element?

八木的驱动元件大约有多长？

234 divided by frequency in MHz

234除以以MHz为单位的频率

1005 divided by frequency in MHz

1005除以频率（MHz）

1/4 wavelength

1/4波长

1/ 2 wavelength

1/ 2 波长

✓ 正确答案

#E9D06🔗

What happens to SWR bandwidth when one or more loading coils are used to resonate an electrically short antenna?

当使用一个或多个负载线圈使电短天线谐振时，SWR 带宽会发生什么变化？

It is increased

增加了

It is decreased

减少了

✓ 正确答案

It is unchanged if the loading coil is located at the feed point

如果加载线圈位于馈电点则不变

It is unchanged if the loading coil is located at a voltage maximum point

如果加载线圈位于电压最大点则不变

#E9D07🔗

What is an advantage of top loading an electrically short HF vertical antenna?

顶部装载电短高频垂直天线有什么优点？

Lower Q

降低Q值

Greater structural strength

更高的结构强度

Higher losses

更高的损失

Improved radiation efficiency

提高辐射效率

✓ 正确答案

#E9D08🔗

What happens as the Q of an antenna increases?

当天线的 Q 值增加时会发生什么？

SWR bandwidth increases

SWR 带宽增加

SWR bandwidth decreases

SWR 带宽降低

✓ 正确答案

Gain is reduced

增益减少

More common-mode current is present on the feed line

馈线上存在更多共模电流

#E9D09🔗

What is the function of a loading coil in an electrically short antenna?

电短天线中加载线圈的作用是什么？

To increase the SWR bandwidth by increasing net reactance

通过增加净电抗来增加 SWR 带宽

To lower the losses

为降低损失

To lower the Q

降低Q值

To resonate the antenna by cancelling the capacitive reactance

通过消除容抗使天线谐振

✓ 正确答案

#E9D10🔗

How does radiation resistance of a base-fed whip antenna change below its resonant frequency?

基馈拉杆天线的辐射电阻在低于其谐振频率时如何变化？

Radiation resistance increases

抗辐射能力增加

Radiation resistance decreases

抗辐射能力下降

✓ 正确答案

Radiation resistance becomes imaginary

抗辐射能力变得虚无缥缈

Radiation resistance does not depend on frequency

辐射电阻与频率无关

#E9D11🔗

Why do most two-element Yagis with normal spacing have a reflector instead of a director?

为什么大多数具有正常间距的二元八木器都有反射器而不是导向器？

Lower SWR

更低驻波比

Higher receiving directivity factor

更高的接收方向性因子

Greater front-to-side

更大的正面到侧面

Higher gain

更高的增益

✓ 正确答案

#E9D12🔗

What is the purpose of making a Yagi’s parasitic elements either longer or shorter than resonance?

让八木的寄生元件比共振更长或更短的目的是什么？

Wind torque cancellation

风扭矩消除

Mechanical balance

机械天平

Control of phase shift

相移控制

✓ 正确答案

Minimize losses

最大限度地减少损失

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FCC E9D - 天线与传输线系统

小节 E9D：天线与传输线系统