CRAC Bilingual Manual › Part: Radio System Fundamentals
CRAC Bilingual Exam Manual (Class A / B / C) | 中国业余无线电台操作技术能力验证英中对照手册
This section covers Antenna Fundamentals with 70 bilingual questions from the CRAC 2025 question bank. Each question shows the original Chinese (left) and the English translation (right). The correct answer is highlighted in green, followed by a Knowledge Point Analysis and Candidate Tips covering US–China differences, common pitfalls, and real on-air practice.
Class badges ABC indicate which license-class syllabus includes each question. Class A is the entry level, Class B adds HF privileges, and Class C is the advanced level.
发射天线的作用是：
- A把发射机输出的射频信号转化为无线电波
- B利用天线的增益放大发射机的输出功率
- C将发射机输出的射频信号转化为音频信号
- D将发射机输出的射频信号转化为红外线
The function of a transmitting antenna is:
- Aconvert the RF signal output by the transmitter into radio waves
- Buse the antenna’s gain to amplify the transmitter’s output power
- Cconvert the RF signal output by the transmitter into an audio signal
- Dconvert the RF signal output by the transmitter into infrared rays
An antenna (天线) is a transducer: it converts the guided RF current from the transmitter into radiating electromagnetic waves (radio waves). Option A is correct. Gain (B) is a directional focusing effect, not power amplification; an antenna does not generate power. C is a receiver/detector function; D is wrong.
US–China difference: Same basic antenna definition in US exams (antenna = converter between guided waves and free-space waves).
Common pitfall: Thinking antenna “gain” means it amplifies power like a PA. Gain only reshapes radiation (focuses it); total radiated power cannot exceed input minus loss.
Real on-air practice: Your 144 MHz HT feeds the antenna, which radiates the RF as waves toward the repeater — no audio, no IR, just radio waves.
接收天线的作用是：
- A把空间的无线电波转化为接收机中的射频电信号
- B利用天线的增益放大空间的无线电波并将之传向接收机
- C将空间的无线电波转化为接收机中的音频信号
- D将空间的无线电波转化为红外线
The function of a receiving antenna is:
- Aconvert the radio waves in space into RF electrical signals in the receiver
- Buse the antenna’s gain to amplify the radio waves in space and transmit them to the receiver
- Cconvert the radio waves in space into audio signals in the receiver
- Dconvert the radio waves in space into infrared rays
A receiving antenna is the reciprocal of a transmitting one: it intercepts passing radio waves and converts them back into a tiny RF voltage delivered to the receiver input. Option A is correct. Gain (B) focuses, it does not “amplify” free-space waves; audio (C) is produced later by the receiver, not the antenna; D is wrong.
US–China difference: Same reciprocal antenna principle in US exams.
Common pitfall: Expecting the antenna to output audio. It outputs only RF; demodulation happens in the receiver.
Real on-air practice: The 7 MHz dipole captures the DX station’s waves and feeds microvolts of RF into your receiver front end for demodulation.
关于天线的增益，以下说法正确的是：
- A待测天线最大辐射方向上的辐射功率密度与基准天线对应值的比值
- B与参考天线相比，被测天线在某个方向上使信号增强的程度
- C天线辐射的电波功率与输入到天线的射频功率之比
- D天线发热耗散的功率与输入到天线的射频功率之比
Regarding antenna gain, which of the following statements is correct? (Choose all that apply.)
- Athe ratio of the radiation power density in the direction of maximum radiation of the antenna under test to that of the reference antenna
- Bthe degree to which the antenna under test enhances the signal in a certain direction compared with the reference antenna
- Cthe ratio of the radio-wave power radiated by the antenna to the RF power input to the antenna
- Dthe ratio of the power dissipated as heat by the antenna to the RF power input to the antenna
Antenna gain (增益) is a directional measure: the radiation intensity (power density) in the main lobe relative to a reference antenna (isotropic for dBi, dipole for dBd), i.e. how much the antenna concentrates power in a given direction. A and B both express this. C is radiation efficiency (辐射效率), not gain; D is dissipation/loss ratio. Hence A, B correct.
US–China difference: Same gain definition (dBi vs dBd) in US exams; note 0 dBd = 2.15 dBi.
Common pitfall: Conflating gain with efficiency. A high-gain antenna can still be inefficient; gain is about directivity, efficiency is about power lost as heat.
Real on-air practice: A 9 dBi Yagi on 2 m focuses your signal toward the repeater; the “gain” is directionality, not extra power.
以dBi为单位的天线增益是指：
- A待测天线最大辐射方向上的辐射功率密度与理想点源天线对应值之比的dB值
- B待测天线最大辐射方向上的辐射功率密度与半波长偶极天线对应值之比的dB值
- C待测天线最大辐射方向上的辐射功率密度与1/4波长地网天线对应值之比的dB值
- D待测天线最大辐射方向及其（180°）反方向的辐射功率密度测量值之比的dB值
Antenna gain expressed in dBi means:
- Athe dB value of the ratio of the radiation power density in the maximum-radiation direction of the antenna under test to that of an ideal point-source antenna
- Bthe dB value of the ratio of the radiation power density in the maximum-radiation direction of the antenna under test to that of a half-wave dipole antenna
- Cthe dB value of the ratio of the radiation power density in the maximum-radiation direction of the antenna under test to that of a 1/4-wavelength ground-plane antenna
- Dthe dB value of the ratio of the measured radiation power density in the maximum-radiation direction of the antenna under test to that in its opposite (180°) direction
dBi = gain relative to an isotropic (理想点源) radiator — a theoretical point source radiating equally in all directions. So dBi compares your antenna’s main-lobe power density to that of an isotropic source, in dB. Option A is correct. B is the definition of dBd (relative to a half-wave dipole); C and D are other references.
US–China difference: Same — in the US, dBi uses the isotropic reference; dBd uses the dipole. 0 dBd = 2.15 dBi.
Common pitfall: Mixing dBi and dBd. A 3 dBi antenna is 0.85 dBd; confusing the two makes you over- or under-state gain by 2.15 dB.
Real on-air practice: A datasheet says “6 dBi”; you know that’s about 3.85 dBd — modest gain for a 2 m vertical.
什么是“理想点源天线”？对业余无线电又有什么意义？
- A存在于理论中的一种小到一个点，可将发射机输出的全部射频能量都转化为各向同性且均匀辐射的电磁波的假想天线；用作比较实际天线辐射性能的一种全向基准天线
- B一种用于专业通信的增益极高的专用天线，在业余无线电中没有应用价值
- C仅用于无线电测试的一种标准接收天线，发射效果不佳，对业余无线电无用
- D一种带宽近乎无限的高级天线的专利名称，业余无线电业务不需要宽带天线
What is an “ideal point-source antenna”? And what is its significance for amateur radio?
- Aa hypothetical antenna existing only in theory that is small to a point and can convert all the RF energy output by the transmitter into isotropically and uniformly radiating electromagnetic waves; used as an omnidirectional reference antenna for comparing the radiation performance of actual antennas
- Ba special antenna with extremely high gain used for professional communication, of no application value in amateur radio
- Ca standard receiving antenna used only for radio testing, with poor transmitting effect and useless for amateur radio
- Da patented name for a high-grade antenna with nearly infinite bandwidth; the amateur service does not need broadband antennas
The ideal isotropic radiator (理想点源天线) is a theoretical lossless point source that radiates equally in every direction — it cannot be built, but it is the reference for dBi gain. Option A describes it correctly. B/C/D invent false physical antennas; it is purely a mathematical reference.
US–China difference: Same concept and use in US antenna theory; “isotropic” is the universal reference.
Common pitfall: Thinking an isotropic antenna is a real product you can buy. It is only a reference model for gain comparisons.
Real on-air practice: When you read “5 dBi”, the “i” tells you the number is versus the ideal isotropic point source, the benchmark for all gain specs.
以dBd为单位的天线增益是指：
- A待测天线最大辐射方向上的辐射功率密度与半波长偶极天线对应值之比的dB值
- B待测天线最大辐射方向上的辐射功率密度与理想点源天线对应值之比的dB值
- C待测天线最大辐射方向上的辐射功率密度与1/4波长垂直天线对应值之比的dB值
- D待测天线最大辐射方向及其（180°）反方向的辐射功率密度测量值之比的dB值
Antenna gain expressed in dBd means:
- Athe dB value of the ratio of the radiation power density in the maximum-radiation direction of the antenna under test to that of a half-wave dipole antenna
- Bthe dB value of the ratio of the radiation power density in the maximum-radiation direction of the antenna under test to that of an ideal point-source antenna
- Cthe dB value of the ratio of the radiation power density in the maximum-radiation direction of the antenna under test to that of a 1/4-wavelength vertical antenna
- Dthe dB value of the ratio of the measured radiation power density in the maximum-radiation direction of the antenna under test to that in its opposite (180°) direction
dBd = gain relative to a half-wave dipole (半波长偶极天线), which itself has 2.15 dBi. So dBd compares your antenna’s main-lobe density to that of a dipole, in dB. Option A is correct. B is dBi; C and D are other references.
US–China difference: Same — US antenna specs use dBd vs the half-wave dipole; convert: dBd + 2.15 = dBi.
Common pitfall: Treating dBi and dBd as interchangeable. A 3 dBd antenna is 5.15 dBi — a 2.15 dB gap.
Real on-air practice: A beam rated “10 dBi” equals “7.85 dBd”; you convert to compare with a dipole-referenced neighbor’s antenna.
半波振子是能够辐射电波的一种实用天线。为了获得最低输入阻抗，人们通常从中点为这种振子馈电。这就构成了具有两个1/4波长不同电极性区域的谐振偶极天线，亦称半波长偶极天线。这种天线的增益规定为0dBd。那么相比理想点源天线，其增益为：
- A2.15dBi
- B6dBi
- C3dBi
- D1.64dBi
The half-wave dipole is a practical antenna capable of radiating radio waves. To obtain the lowest input impedance, it is usually fed at the center point. This forms a resonant dipole antenna with two 1/4-wavelength regions of different polarity, also called a half-wave dipole. This antenna’s gain is specified as 0 dBd. Then, compared with an ideal point-source antenna, its gain is:
- A2.15 dBi
- B6 dBi
- C3 dBi
- D1.64 dBi
A half-wave dipole has a gain of 0 dBd by definition; since 0 dBd = 2.15 dBi (the dipole is 2.15 dB stronger than an isotropic point source), its gain versus the ideal isotropic antenna is 2.15 dBi. Option A is correct. D (1.64) is the aperture efficiency factor, not the gain in dBi.
US–China difference: Same fixed relation in US antenna math: a dipole = 2.15 dBi = 0 dBd.
Common pitfall: Forgetting to add 2.15 when converting dBd→dBi, or using 1.64 (the directivity of a short dipole) by mistake.
Real on-air practice: You compare your 5 dBi vertical to a dipole: 5 − 2.15 = 2.85 dBd, i.e. modestly better than a half-wave dipole.
某商品天线说明书给出的天线增益指标以dB为单位。其意义为：
- A该指标未指明计算方法和所用基准，缺乏参考价值
- B待测天线最大辐射方向上的辐射功率密度与理想点源天线对应值之比的dB值
- C待测天线最大辐射方向上的辐射功率密度与1/4波长垂直天线对应值之比的dB值
- D待测天线最大辐射方向及其（180°）反方向的辐射功率密度测量值之比的dB值
The antenna gain indicator given in a certain commercial antenna manual is expressed in dB. Its meaning is:
- Athis indicator does not specify the calculation method and the reference used, and lacks reference value
- Bthe dB value of the ratio of the radiation power density in the maximum-radiation direction of the antenna under test to that of an ideal point-source antenna
- Cthe dB value of the ratio of the radiation power density in the maximum-radiation direction of the antenna under test to that of a 1/4-wavelength vertical antenna
- Dthe dB value of the ratio of the measured radiation power density in the maximum-radiation direction of the antenna under test to that in its opposite (180°) direction
A bare “dB” with no stated reference (neither dBi nor dBd) is meaningless for comparing antennas, because gain must be relative to a defined reference antenna. Such a spec lacks reference value. Option A is correct. B is the dBi definition, C a dB-vs-vertical, D a front-to-back ratio — but the question says only “dB” with no basis, so none of those apply.
US–China difference: Same caveat in the US — reputable US vendors state dBi or dBd; a vague “dB gain” claim is a marketing red flag.
Common pitfall: Trusting a “12 dB gain” antenna spec with no reference. Without dBi/dBd it can be inflated or measured against an unrealistic baseline.
Real on-air practice: You skip a “10 dB” mag-mount and buy one clearly marked “3 dBi” so you know what you’re actually getting.
我们之所以称垂直接地天线为“全向天线”，是因为：
- A这种天线在水平方向上没有指向性
- B这种天线在垂直方向上没有指向性
- C这种天线的E面和H面方向图均为正圆
- D这种天线辐射各向同性的球面波
The reason we call a vertical grounded antenna an “omnidirectional antenna” is:
- Athis antenna has no directivity in the horizontal direction
- Bthis antenna has no directivity in the vertical direction
- Cthe E-plane and H-plane radiation patterns of this antenna are both perfect circles
- Dthis antenna radiates isotropic spherical waves
A vertical grounded antenna radiates equally in all compass bearings around it — its horizontal (azimuth) pattern is a circle, i.e. no horizontal directivity — which is why it is called omnidirectional (全向). Option A is correct. It does have vertical (elevation) directivity/nulls (B false); its patterns are not perfect circles in both planes (C false); and it is not truly isotropic (D false — only an ideal point source is isotropic).
US–China difference: Same “vertical = omnidirectional in azimuth” concept in US antenna basics.
Common pitfall: Thinking “omnidirectional” means equal in all 3D directions. It is omnidirectional only horizontally; vertically it has lobes and nulls (e.g. a null straight up).
Real on-air practice: Your 2 m vertical works equally to repeaters north, south, east, west — great for local coverage, but it wastes energy straight up (useless for satellites without an elevation beam).
如需垂直接地天线在大体为零仰角的水平发射方向上具有主辐射瓣并可以与同轴电缆直接耦合，则振子长度应选为：
- A1/4波长
- B1/2波长
- C1/8波长
- D3/2波长
If a vertically grounded (ground-plane) antenna is required to have a main lobe at a horizontal launch angle of approximately zero elevation and to be directly coupled to a coaxial cable, the element length should be chosen as:
- A1/4 wavelength
- B1/2 wavelength
- C1/8 wavelength
- D3/2 wavelength
A ground-plane antenna with a quarter-wavelength vertical element over a ground plane radiates its main lobe horizontally (near 0° elevation) and presents a feed-point impedance of about 50 Ω, which matches coaxial cable directly — so 1/4 wavelength is correct. A half-wave or 3/2-wavelength vertical has a high feed-point impedance and a different pattern; 1/8 wavelength is too short to be resonant.
US–China difference: Same principle applies in the US; a 1/4-wave ground-plane is the classic VHF/UHF vertical, matched to 50 Ω coax.
Common pitfall: Picking 1/2 wavelength, forgetting that a ground-plane’s element is only a quarter-wave over its image.
Real on-air practice: A 2 m (144 MHz) ground-plane uses a ~0.5 m element — easy to couple straight to your coax.
关于振子长度为1/4波长的垂直接地天线的最大辐射方向，以下描述正确的是：
- A在水平方向上是全向的
- B在垂直方向上有指向性，且辐射仰角稍大于0°
- C其E面方向图为“8”字形
- D其H面方向图为“8”字形
Regarding the maximum-radiation direction of a vertically grounded (ground-plane) antenna whose element is 1/4 wavelength long, which of the following descriptions is correct? (Choose all that apply.)
- AIt is omnidirectional in the horizontal direction
- BIt is directional in the vertical direction, and the radiation elevation angle is slightly greater than 0°
- CIts E-plane pattern is “figure-8”
- DIts H-plane pattern is “figure-8”
A quarter-wave ground-plane antenna radiates omnidirectionally around the azimuth (H-plane, horizontal) and has its main lobe slightly above 0° elevation in the vertical (E-plane) cut — so A and B are correct. The figure-8 pattern belongs to a dipole’s E-plane, not to a vertical ground-plane; C and D are wrong.
US–China difference: Identical antenna theory in the US; the H-plane of a vertical is the horizontal “donut”.
Common pitfall: Assigning the figure-8 to the vertical ground-plane instead of to a dipole.
Real on-air practice: A 2 m vertical gives you coverage in every compass direction from your QTH.
关于大多数手持电台随附的“橡胶天线”，以下说法正确的是：
- A就电台的一般持握方式而言，电波的垂直极化分量要强一些
- B相对于全尺寸天线，“橡胶天线”的发射与接收增益都低一些
- C如果橡胶护套内的天线是螺旋加感的，则电波是旋转极化的
- D如果橡胶护套某处开裂，则振子会迅速解体，天线随即报废
Which of the following statements about the “rubber-duck” antennas supplied with most handheld transceivers is correct? (Choose all that apply.)
- AGiven the usual way the radio is held, the vertically polarized component of the wave is stronger
- BCompared with full-size antennas, the rubber-duck antenna has lower transmit and receive gain
- CIf the antenna inside the rubber sheath is helically loaded, the wave is circularly polarized (rotating polarization)
- DIf the rubber sheath cracks somewhere, the element quickly disintegrates and the antenna is immediately useless
A rubber-duck is normally held vertically, so the vertical polarization component dominates (A). Because it is physically shorter than a full-size 1/4-wave element, it has lower gain on both transmit and receive (B). Helical loading does not make the radiated wave circularly polarized (C is wrong), and a cracked sheath does not instantly destroy the internal element (D is wrong).
US–China difference: Rubber-duck antennas are just as common on US handhelds (HTs) for the same reasons.
Common pitfall: Thinking a helically loaded rubber-duck is circularly polarized.
Real on-air practice: Hold your HT upright for the strongest signal into a vertical repeater.
在车内使用手持电台和俗称“橡胶天线”的柔性天线进行通信可能遇到什么问题？
- A车体的屏蔽作用影响信号强度
- B大量电波反射回天线，抬升SWR
- C影响电台散热
- D行车噪声影响通话质量
What problem may be encountered when using a handheld transceiver with a flexible “rubber-duck” antenna for communication inside a vehicle?
- AThe shielding effect of the vehicle body affects signal strength
- BA large amount of radio waves are reflected back to the antenna, raising the SWR
- CIt affects the transceiver’s heat dissipation
- DDriving noise affects the quality of the conversation
Inside a metal vehicle, the body acts like a Faraday shield, attenuating the rubber-duck’s signal (A). Reflected waves raising the SWR (B), poor heat dissipation (C), and road noise on the audio (D) are not the characteristic problem of operating a rubber-duck inside a car.
US–China difference: Same issue in the US; hams use an external mag-mount antenna through the glass or roof instead.
Common pitfall: Blaming the SWR rather than the body shielding for weak signal.
Real on-air practice: Put a rubber-duck near a window, or better use an exterior antenna, for mobile work.
如果架设天线时发现场地附近有电线等市电供电装置，你该怎么办？
- A应确保在风雨中意外掉落的天线部件不落入供电装置的安全距离内。例如，35千伏及以下电压时至少1米
- B应确保供电装置带来的电源噪声不会影响电台接收弱信号的能力。通常，这个距离应至少10倍于工作波长
- C必须防止通信和供电两套系统之间发生打火拉弧事故。经验上讲，按照每千伏1毫米算出的间距是足够的
- D应确保天线转动到平行于供电系统的电线时，电线不会成为反射单元，即，应至少保持1/4波长以上距离
If, when erecting an antenna, you find mains-powered equipment such as power lines near the site, what should you do?
- AEnsure that antenna parts accidentally falling in wind and rain do not enter the safety distance of the power-supply equipment. For example, at 35 kV and below the distance should be at least 1 meter
- BEnsure that power-supply noise does not affect the station’s ability to receive weak signals. Usually this distance should be at least 10 times the operating wavelength
- CYou must prevent arcing between the communication and power systems. Empirically, a spacing calculated at 1 mm per kV is sufficient
- DEnsure that when the antenna rotates to be parallel to the power lines, the lines do not become a reflector element, i.e., keep at least 1/4 wavelength distance
Safety is paramount: any antenna part that might fall must stay outside the power equipment’s safety clearance (at least 1 m at 35 kV and below) to avoid electrocution or short-circuit (A). The other options give incorrect or irrelevant distance criteria (10× wavelength, 1 mm/kV, 1/4 wavelength are not the correct safety rule).
US–China difference: US hams follow the same “keep clear of power lines” safety rule; local electrical codes set the clearances.
Common pitfall: Confusing RF separation distances with electrical safety clearances.
Real on-air practice: Route your antenna well away from overhead wires — a fallen mast near lines is lethal.
垂直接地天线（GP）由电气长度为1/4波长的垂直振子加上一个“镜像地平面”构成，因十分简洁而被大量应用于手持和车载业余通信。但是，这种天线的工作有效性往往不如理论预计的那么完美，特别是在波长较长的波段。造成这种情况的原因及改善方法是：
- A缺乏有效接地镜像；GP天线必须有足够大的导电平面以形成振子镜像，否则谐振频率和阻抗都与理论值有出入。为此，应尽量用大面积金属导体与天线/馈线的接地端相连
- B1/4波长垂直振子显然是太短了。改成1/2波长即可解决问题
- C1/4波长垂直振子显然是太短了。在振子当中串联加感线圈即可解决问题
- D天线与电缆直接相连，匹配不佳。在天线和电缆之间加接“巴伦”即可解决问题
The vertically grounded antenna (GP) consists of a vertical element with an electrical length of 1/4 wavelength plus an “image ground plane”, and because it is very simple it is widely used in handheld and mobile amateur communication. However, its actual effectiveness is often not as perfect as theory predicts, especially on longer-wavelength bands. The cause and improvement method are:
- ALack of an effective grounded image; a GP antenna must have a sufficiently large conductive plane to form the element image, otherwise the resonant frequency and impedance deviate from theoretical values. Therefore, connect as large a metal conductor as possible to the ground terminal of the antenna/feed line
- BA 1/4-wavelength vertical element is obviously too short. Changing to 1/2 wavelength solves the problem
- CA 1/4-wavelength vertical element is obviously too short. Inserting a loading coil in series in the element solves the problem
- DThe antenna connects directly to the cable, with poor matching. Adding a “balun” between the antenna and cable solves the problem
A GP needs a real ground/radial plane to form the image of the element; without enough conductive area the resonance and impedance shift from theory, so connecting a large metal ground plane is the correct fix (A). Lengthening to 1/2 λ changes the antenna type (B), loading coils don’t fix a missing ground (C), and a balun is not the issue for an unbalanced vertical (D).
US–China difference: US mobile GPs use radial wires or a metal roof/car body as the ground plane — same concept.
Common pitfall: Expecting a GP to work well without an adequate ground plane (radials).
Real on-air practice: Add several 1/4-wave radials to a base GP to recover the expected low SWR.
关于天线的加载，以下描述正确的是
- A为天线振子串联电感线圈，延长振子的电气长度
- B为车载天线增添弹簧减震器
- C为柔性不足的天线基座增加螺旋式延长器
- D为八木天线的拉纤加接弹性张力器
Which of the following descriptions about antenna loading is correct?
- AConnecting an inductive coil in series with the antenna element to extend its electrical length
- BAdding a spring shock absorber to a mobile antenna
- CAdding a helical extender to an antenna base that lacks flexibility
- DAdding an elastic tensioner to the guy wires of a Yagi antenna
Loading an antenna means adding reactance (typically a series inductor) to the element so it behaves electrically longer than its physical length (A). The other options describe mechanical accessories (spring, extender, guy tensioner), not electrical loading.
US–China difference: Inductive loading is used the same way on US mobile HF antennas (e.g., a loaded whip).
Common pitfall: Confusing a mechanical spring base with electrical loading.
Real on-air practice: A loaded 40 m mobile whip lets you operate without a full-size antenna.
谐振的垂直接地天线的振子长度最短也要1/4波长。如果架设天线时因条件受限而不得不将振子缩短，那么在振子之中串入电感可以补偿失去的感抗，使天线谐振在所需频率上。为了提高发射效率，应在振子的什么位置串入电感需根据架设条件择优确定。下图给出三种加感方案。假设振子（灰色部分）均等长，则A、B、C三种方案按发射效率可排列为：
- AC-顶部加感，B-中部加感，A-底部加感
- BA-底部加感，B-中部加感，C-顶部加感
- CA-底部加感，C-顶部加感，B-中部加感
- DB-中部加感，A-底部加感，C-顶部加感 [F]LK0944.jpg
The element of a resonant vertically grounded antenna must be at least 1/4 wavelength long. If site constraints force you to shorten the element, inserting an inductor in series can compensate for the lost reactance and resonate the antenna at the desired frequency. To improve radiation efficiency, where in the element to insert the inductor depends on the site. The figure shows three loading schemes. Assuming the (gray) elements are equal in length, the A, B, C schemes ranked by radiation efficiency are:
- AC-top loading, B-middle loading, A-bottom loading
- BA-bottom loading, B-middle loading, C-top loading
- CA-bottom loading, C-top loading, B-middle loading
- DB-middle loading, A-bottom loading, C-top loading [F]LK0944.jpg
For a shortened vertical, top loading (scheme C) places the inductive reactance where the current is highest, giving the largest effective current moment and thus the best efficiency; middle loading (B) is next, and base loading (A) is worst. So the efficiency order is C > B > A, which is exactly option A (C-top, B-middle, A-bottom).
US–China difference: US loaded mobile whips use the same rule — top (center) loading beats base loading for efficiency.
Common pitfall: Assuming base loading is best because it is easiest to build; it is actually the least efficient.
Real on-air practice: A base-loaded 40 m whip loses more power in the coil than a center-loaded one.
甲天线增益6.15dBi，乙天线增益1dBd。若两副天线按同样条件架设并用同样功率来驱动，则在它们最大发射方向的同一远方地点接收时，两天线给出的信号功率关系为：
- A甲天线的信号功率为乙天线的两倍
- B甲天线的信号功率为乙天线的1/2
- C甲天线的信号功率为乙天线的5.15倍
- D甲天线的信号功率为乙天线的6.15倍
Antenna A has a gain of 6.15 dBi and antenna B has a gain of 1 dBd. If both antennas are erected under the same conditions and driven with the same power, then at the same distant location in their maximum-radiation direction, the signal-power relationship is:
- AAntenna A’s signal power is twice that of antenna B
- BAntenna A’s signal power is 1/2 that of antenna B
- CAntenna A’s signal power is 5.15 times that of antenna B
- DAntenna A’s signal power is 6.15 times that of antenna B
Gain references must be converted before comparing: 1 dBd = 2.15 dBi, so antenna B = 1 + 2.15 = 3.15 dBi. Antenna A = 6.15 dBi. The difference is 6.15 − 3.15 = 3.0 dB, which is a power ratio of 10^(3/10) ≈ 2.0. So A’s signal is twice B’s. Options C and D are wrong because you cannot subtract dBi and dBd directly.
US–China difference: Same dBi/dBd math in the US; memorize 0 dBd = 2.15 dBi.
Common pitfall: Subtracting 6.15 − 1 = 5.15 and claiming a 5.15× ratio.
Real on-air practice: A 3 dB antenna improvement doubles your received signal.
甲天线增益0dBd，乙天线增益2dBi。若两副天线按同样条件架设用用同样功率来驱动，则在它们最大发射方向的同一远方地点接收时，两天线给出的信号功率关系为：
- A甲天线的效果与半波长偶极天线相当，乙天线比甲天线略差
- B甲天线效果为零，不能工作，乙天线效果比甲天线好2倍
- C甲天线的效果与半波长偶极天线相当，乙天线发射的信号强度比甲天线好2dB
- D甲、乙天线的效果实际相同
Antenna A has a gain of 0 dBd and antenna B has a gain of 2 dBi. If both are erected under the same conditions and driven with the same power, then at the same distant location in their maximum-radiation direction, the signal-power relationship is:
- AAntenna A’s effect is equivalent to a half-wave dipole, and antenna B is slightly worse than antenna A
- BAntenna A’s effect is zero, it cannot work, and antenna B is twice as good as antenna A
- CAntenna A’s effect is equivalent to a half-wave dipole, and antenna B transmits a signal 2 dB stronger than antenna A
- DAntennas A and B are actually the same
0 dBd means equal to a half-wave dipole, so antenna A ≈ dipole. Convert B: 2 dBi − 2.15 = −0.15 dBd, i.e., slightly LESS than a dipole. Thus B (2 dBi) is slightly weaker than A (0 dBd). Option A is correct; C (claiming B is 2 dB stronger) and D (equivalent) are wrong.
US–China difference: Same reference conversion; US catalogs often list antenna gain in dBi.
Common pitfall: Thinking 2 dBi > 0 dBd because 2 > 0 numerically, forgetting the 2.15 dB offset.
Real on-air practice: A dipole (2.15 dBi) is your 0 dBd reference for comparing antennas.
有两款VHF垂直全向天线作发射之用。甲天线增益为4.5dBd，而乙天线的是5.85dBi。它们在远处某接收天线中产生的信号功率有什么不同？
- A来自甲天线的信号比乙天线的强0.8dB
- B来自乙天线的信号比甲天线的强1.35dB
- C来自甲天线的信号比乙天线的强1.35dB
- D来自乙天线的信号比甲天线的强3.5dB
Two VHF vertical omnidirectional antennas are used for transmitting. Antenna A has a gain of 4.5 dBd and antenna B has a gain of 5.85 dBi. How do the signal powers they produce at a distant receiving antenna differ?
- AThe signal from antenna A is 0.8 dB stronger than that from antenna B
- BThe signal from antenna B is 1.35 dB stronger than that from antenna A
- CThe signal from antenna A is 1.35 dB stronger than that from antenna B
- DThe signal from antenna B is 3.5 dB stronger than that from antenna A
Convert to a common reference: antenna A = 4.5 dBd = 4.5 + 2.15 = 6.65 dBi. Antenna B = 5.85 dBi. The difference is 6.65 − 5.85 = 0.8 dB, so A is 0.8 dB stronger. Correct answer is A.
US–China difference: Same dBi/dBd conversion everywhere.
Common pitfall: Subtracting 5.85 − 4.5 = 1.35 and wrongly concluding B is stronger.
Real on-air practice: Always convert gain specs to the same reference before comparing two antennas.
有两款VHF垂直全向天线作发射之用。甲天线增益为2.9dBd，而乙天线的是5.85dBi。它们在远处某接收天线中产生的信号功率有什么不同？
- A来自乙天线的信号比甲天线的强0.8dB
- B来自乙天线的信号比甲天线的强2.95dB
- C来自甲天线的信号比乙天线的强2.95dB
- D来自乙天线的信号比甲天线的强7.1dB
Two VHF vertical omnidirectional antennas are used for transmitting. Antenna A has a gain of 2.9 dBd and antenna B has a gain of 5.85 dBi. How do the signal powers they produce at a distant receiving antenna differ?
- AThe signal from antenna B is 0.8 dB stronger than that from antenna A
- BThe signal from antenna B is 2.95 dB stronger than that from antenna A
- CThe signal from antenna A is 2.95 dB stronger than that from antenna B
- DThe signal from antenna B is 7.1 dB stronger than that from antenna A
Convert: antenna A = 2.9 dBd = 2.9 + 2.15 = 5.05 dBi. Antenna B = 5.85 dBi. Difference = 5.85 − 5.05 = 0.8 dB, so B is 0.8 dB stronger. Correct answer is A.
US–China difference: Same worldwide antenna math.
Common pitfall: Subtracting 5.85 − 2.9 = 2.95 and claiming a 2.95 dB edge for B.
Real on-air practice: That 0.8 dB is barely audible; both antennas are nearly equal.
业余无线电爱好者讨论天线系统时常会提及术语“驻波比（SWR）”。其含义为：
- A连接到传输线终端的负载阻抗与传输线自身的特性阻抗相匹配的程度
- B负载与传输线完美匹配时，传输线之中没有驻波，因此驻波比为1:1
- C如果负载与传输线不匹配，传向负载的部分能量会沿传输线返回始端
- D如果传输线中出现驻波，则调整传输线始端的信源阻抗可使驻波归零
When amateur radio operators discuss antenna systems they often mention the term “standing-wave ratio (SWR)”. Its meaning is: (Choose all that apply.)
- AThe degree to which the load impedance connected to the end of the transmission line matches the transmission line’s own characteristic impedance
- BWhen the load and transmission line are perfectly matched, there are no standing waves on the line, so the SWR is 1:1
- CIf the load and transmission line are mismatched, part of the energy traveling toward the load is reflected back along the line to the source
- DIf standing waves appear on the transmission line, adjusting the source impedance at the line’s beginning can reduce the standing waves to zero
SWR measures how well the load impedance matches the line’s characteristic impedance (A); perfect match means no standing wave and SWR = 1:1 (B); a mismatch reflects part of the forward energy back toward the source (C). D is wrong: you cannot cancel standing waves by adjusting only the source end — the mismatch at the load (or a matching network) must be addressed.
US–China difference: SWR is defined identically under FCC Part 97 practice and ITU terms.
Common pitfall: Thinking you can “tune out” an antenna mismatch at the radio end alone.
Real on-air practice: An SWR of 1.5:1 or less is typical and fine; 1:1 is ideal.
通联时，如果收发信机的SWR表显示读数4:1，则意味着：
- A从发射机的输出端口来看，天线系统的整体匹配情况不佳
- B从发射机的输出端口来看，天线系统的整体阻抗为200欧或12.5欧
- C天线系统的辐射效率仅为25%
- D天线系统的整体增益仅为4dB
During a contact, if the transceiver’s SWR meter reads 4:1, this means:
- AViewed from the transmitter’s output port, the overall matching of the antenna system is poor
- BViewed from the transmitter’s output port, the antenna system’s overall impedance is 200 Ω or 12.5 Ω
- CThe antenna system’s radiation efficiency is only 25%
- DThe antenna system’s overall gain is only 4 dB
An SWR of 4:1 simply indicates poor overall matching as seen at the transmitter port (A). The reading by itself does not determine a unique impedance, nor does it state efficiency (C) or gain (D). (Note: with a known 50 Ω reference a 4:1 SWR could correspond to 200 Ω or 12.5 Ω, but the question’s answer key marks only A as the correct statement.)
US–China difference: Same interpretation of an SWR reading on any transceiver.
Common pitfall: Equating the “4” in 4:1 with efficiency percent or gain in dB.
Real on-air practice: A 4:1 reading tells you to check your feed/antenna, not that your gain dropped to 4 dB.
小强用长度不短于1/4波长的50欧馈线连接收发信机和天线。发信时，他发现SWR表的指示为3:1。该值意味着：
- A馈线中任意位置上的最大峰值电压与最小峰值电压之比为3:1
- B馈线中任意位置上的最大峰值电流与最小峰值电流之比为3:1
- C馈线中的驻波致使平均射频电压高于常值，这降低了导体损耗
- D馈线中的驻波致使平均射频电流高于常值，这降低了介质损耗
Xiaoqiang uses a 50 Ω feed line no shorter than 1/4 wavelength to connect the transceiver and antenna. While transmitting he finds the SWR meter indicates 3:1. This value means: (Choose all that apply.)
- AThe ratio of the maximum to minimum peak voltage anywhere on the feed line is 3:1
- BThe ratio of the maximum to minimum peak current anywhere on the feed line is 3:1
- CThe standing wave on the feed line raises the average RF voltage above normal, which reduces conductor loss
- DThe standing wave on the feed line raises the average RF current above normal, which reduces dielectric loss
SWR is the ratio of the maximum to minimum envelope of the standing wave along the line — equally valid for voltage (A) or current (B), since the standing-wave ratio is the same for both. C and D are false: standing waves increase peak voltage/current and raise losses; they do not reduce them.
US–China difference: Same SWR definition in the US.
Common pitfall: Thinking a high SWR lowers loss — the opposite is true; peaks stress components.
Real on-air practice: A 3:1 SWR means voltage peaks 3× the RMS envelope along your coax.
多数发射机都在SWR超过一定值时降低输出功率。这是为了：
- A保护发射机中的功率半导体器件
- B防止烧断供电线路中的保险丝
- C防止传输线上的驻波超过限值
- D防止发射出去的无线电波带有过大的驻波
Most transmitters reduce output power when the SWR exceeds a certain value. This is in order to:
- AProtect the power semiconductor devices in the transmitter
- BPrevent blowing the fuse in the power-supply line
- CPrevent the standing wave on the transmission line from exceeding the limit
- DPrevent the radiated radio wave from carrying an excessive standing wave
A high SWR makes the power amplifier see a bad load, which can overheat and damage the final power semiconductors, so reducing power protects them (A). SWR exists on the feed line, not “inside the radiated wave” (D), and fuses/line limits are not the reason (B, C).
US–China difference: Modern US transceivers also fold back power on high SWR for the same PA-protection reason.
Common pitfall: Thinking the transmitter reduces power to protect the feed line rather than its own finals.
Real on-air practice: If your radio drops power, check the antenna — it is saving its finals.
用同轴电缆连接天线时，为什么驻波比趋于1:1为好？
- A降低电缆的损耗，使射频能量更有效地传输
- B防止屏蔽层的外层辐射能量，导致射频干扰（RFI）
- C延长天线的使用寿命
- D延长发信机的使用寿命
When connecting an antenna with coaxial cable, why is it better for the SWR to approach 1:1?
- AIt reduces cable loss, so RF energy is transferred more efficiently
- BIt prevents the shield’s outer conductor from radiating energy, causing RFI
- CIt extends the antenna’s service life
- DIt extends the transceiver’s service life
Lower SWR means less reflected power and therefore less additional loss in the feed line, improving transfer efficiency (A). Option B concerns common-mode currents (a separate issue addressed by a balun/chokes), and C/D are unrelated to SWR.
US–China difference: Same reason hams aim for low SWR in the US.
Common pitfall: Thinking a low SWR prevents RFI — that is a common-mode, not an SWR, problem.
Real on-air practice: A long lossy coax with 2:1 SWR loses noticeably more power than at 1:1.
以下哪种情况可能导致业余发信机显示的驻波比不稳定？
- A发信机、馈线或天线某处接触不良
- B发信机采用相位调制
- C发信机过调制
- D馈线温度过高
Which of the following situations may cause the SWR displayed by an amateur transmitter to be unstable?
- APoor contact somewhere in the transmitter, feed line, or antenna
- BThe transmitter uses phase modulation
- CThe transmitter is over-modulated
- DThe feed line temperature is too high
Intermittent or poor connections make the impedance vary, so the SWR reading jumps around (A). Phase modulation, over-modulation, or simply high cable temperature do not by themselves make the SWR reading unstable.
US–China difference: Same troubleshooting logic worldwide.
Common pitfall: Blaming modulation type for an unstable SWR instead of a loose connector.
Real on-air practice: Wiggle your PL-259/SO-239 joints; a flickering SWR often means a bad contact.
SSB通联时，即使天馈系统没有故障，有时候SWR显示也不稳定。这是因为：
- ASSB话音的幅度变化本质上影响测量的稳定性。改用CW方式进行测量效果更好
- BSSB话音包含幅度与相位两种信息，并非所有天线均能同时给出稳定的响应
- C出现这种情况是因为发信机过调制，应调整话筒增益以解决
- D出现这种情况说明发信机出了故障，应停机检修
During SSB contacts, even when the antenna/feed system has no fault, the SWR reading is sometimes unstable. This is because:
- AThe amplitude variation of SSB speech inherently affects measurement stability. Using CW for measurement gives better results
- BSSB speech contains both amplitude and phase information, and not all antennas can give a stable response simultaneously
- CThis occurs because the transmitter is over-modulated; microphone gain should be adjusted to fix it
- DThis indicates a transmitter fault; it should be shut down for repair
An SWR meter samples the RF envelope amplitude; SSB voice has a constantly varying envelope, so the reading fluctuates even with a healthy system. Measuring on a steady carrier (CW) gives a stable value (A). B/C/D misattribute the fluctuation to the antenna, over-modulation, or a fault.
US–China difference: US hams also measure SWR on a CW/dummy-load tone for a steady reading.
Common pitfall: Concluding the antenna is bad just because SSB SWR bounces around.
Real on-air practice: Key the radio in TUNE/CW to read a stable SWR.
我们都知道发射机与天线间的馈线应当与天线阻抗匹配。否则，馈线中的驻波会使沿线各处的电压和电流周期性起伏。然而，业余电台所用的发射机与电网中的发电机同属交流电源，我们却从未在连到电网的电线中观察到驻波现象。这是为什么？
- A电网供电的频率很低，导线长度与波长相比微不足道，驻波现象不明显而已
- B业余电台所用的馈线和电网中的电线工作原理不同，所以现象不尽相同
- C适用于供电技术和业余无线电的电学理论本质不同，所以现象自然不同
- D电网的供电能力远超发射机所能提供的电功率，这就迫使线路各处电压趋同
We all know the feed line between transmitter and antenna should match the antenna impedance. Otherwise, standing waves in the feed line cause periodic rises and falls of voltage and current along the line. Yet the transmitter used in amateur radio and the generator in the power grid are both AC sources, yet we never observe standing waves in power-line wires. Why?
- AThe power grid’s frequency is very low, so the wire length is negligible compared with the wavelength, and standing-wave phenomena are not noticeable
- BThe feed lines used in amateur radio and the wires in the power grid work on different principles, so the phenomena differ
- CThe electrical theory applicable to power technology and to amateur radio is essentially different, so the phenomena naturally differ
- DThe power grid’s supply capacity far exceeds what the transmitter can provide, forcing the voltage everywhere on the line to equalize
Standing waves are only observable when the line length is a significant fraction of a wavelength. Mains is 50/60 Hz (wavelength of thousands of km), so household wiring is tiny compared to λ → no visible SWR (A). The underlying physics is the same; only the scale differs, so B/C/D are wrong.
US–China difference: Same transmission-line physics; US power lines also show no SWR for the same reason.
Common pitfall: Thinking power wiring follows different laws than RF feed lines.
Real on-air practice: On 160 m even a few meters of feed line matters; on 60 Hz it never does.
对于业余无线电通信，最适合的同轴电缆特性阻抗为：
- A50欧姆
- B75欧姆
- C93欧姆
- D300欧姆
For amateur radio communication, the most suitable characteristic impedance of coaxial cable is:
- A50 ohms
- B75 ohms
- C93 ohms
- D300 ohms
Amateur transmitters, receivers, and antennas are designed around 50 Ω coax (A). 75 Ω is CATV, 300 Ω is twin-lead (not coax), and 93 Ω is uncommon for our use.
US–China difference: 50 Ω is the amateur standard in the US as well (FCC Part 97 equipment).
Common pitfall: Using 75 Ω TV coax for the shack and wondering about high SWR.
Real on-air practice: Your rig, SWR meter, and antenna all expect 50 Ω.
传输线具有多种类型，但是为什么架设业余电台通常选用同轴电缆？
- A因为它易于使用，与架设环境之中其他物体间的互耦也很低
- B因为它的损耗比其他任何种类的馈线都低
- C因为相比其他馈线，它可以传输更大的功率
- D因为很明显，它比其他任何馈线都便宜
Transmission lines come in many types, but why is coaxial cable usually chosen when setting up an amateur station?
- ABecause it is easy to use and has very low mutual coupling with other objects in the environment
- BBecause its loss is lower than any other kind of feed line
- CBecause, compared with other feed lines, it can transmit greater power
- DBecause it is obviously cheaper than any other feed line
Coax is unbalanced and shielded, so it is easy to route and has low coupling to nearby objects (A). It is not the lowest-loss (air-dielectric line wins), nor necessarily the highest-power or cheapest (B/C/D are wrong).
US–China difference: US hams likewise default to coax for convenience and shielding.
Common pitfall: Believing coax has the lowest loss of all feed lines.
Real on-air practice: Coax runs cleanly next to your tower and house without radiating.
在为业余电台选购用作天线馈线的同轴电缆时应关注什么电气参数？
- A特性阻抗
- B指定频率下每百米的传输损耗
- C芯线的截面积和最大额定电流
- D电介质的耐压和最高允许温升
When purchasing coaxial cable for use as an antenna feed line for an amateur station, which electrical parameters should you pay attention to? (Choose all that apply.)
- ACharacteristic impedance
- BTransmission loss per 100 m at the specified frequency
- CThe cross-sectional area of the center conductor and its maximum rated current
- DThe dielectric’s withstand voltage and maximum allowable temperature rise
The key RF selection parameters are characteristic impedance (must match 50 Ω for a good match) and attenuation per unit length at your operating frequency (A, B). Center-conductor cross-section/current rating and dielectric voltage/temperature (C, D) matter for DC power wiring but are not the primary criteria for choosing an RF feed line.
US–China difference: US hams check the same specs (impedance, loss @ MHz) when buying coax.
Common pitfall: Focusing on wire gauge/current rating instead of RF loss and impedance.
Real on-air practice: Pick RG-213 or LMR-400 by its loss per 100 m at 432 MHz.
我们都知道要为业余电台选配损耗较低的馈线。但是，馈线的损耗会导致什么问题？
- A发信功率降低
- B收信信噪比下降
- C驻波比的测量值永远高于1:1
- D发出的信号失真
We all know to choose a low-loss feed line for the amateur station. But what problems can feed-line loss cause? (Choose all that apply.)
- AReduced transmit power
- BReduced receive signal-to-noise ratio
- CThe SWR measurement is always higher than 1:1
- DThe transmitted signal is distorted
Loss attenuates the forward signal so less power radiates (A), and on receive the loss is ahead of the receiver, lowering the SNR (B). Loss does not by itself force SWR > 1 (C) nor distort the signal (D).
US–China difference: Same effect; US hams keep coax runs short on UHF for this reason.
Common pitfall: Thinking feed-line loss changes the SWR reading (it doesn’t, at the transmitter).
Real on-air practice: On a 70 cm repeater, thin coax can eat half your power.
受潮是同轴电缆失效损坏的主要原因。湿气渗透会导致：
- A介质损耗变大
- B屏蔽层或芯线氧化、锈蚀，甚至断路
- C速度因子逐渐大于1
- D驻波比越来越小于1
Moisture ingress is a main cause of coaxial cable failure and damage. Moisture penetration can cause: (Choose all that apply.)
- ADielectric loss to increase
- BThe shield or center conductor to oxidize, rust, and even break open (open circuit)
- CThe velocity factor to gradually become greater than 1
- DThe SWR to become smaller and smaller, below 1
Water raises the dielectric constant and loss, and corrodes the conductors, increasing loss (A) and eventually causing opens (B). The velocity factor can never exceed 1 (C), and SWR is always ≥ 1 (D) — both are physically impossible, so they are wrong.
US–China difference: US hams also seal coax ends with self-amalgamating tape for the same reason.
Common pitfall: Thinking water could make velocity factor > 1 (impossible).
Real on-air practice: Water in the coax turns a clear signal into mush — seal every connector.
将同轴电缆装于室外时，为什么要求电缆外皮（护套）能够耐受紫外线？
- A如果电缆护套被紫外线破坏，电缆就会受潮损坏
- B紫外线会激励非线性导行模式，导致互调和谐波发射
- C紫外线会与射频信号相互混频，导致相当复杂的宽带干扰
- D紫外线会促使电缆升温，并因此增加电缆的功率损耗
When installing coaxial cable outdoors, why is the cable jacket required to resist ultraviolet (UV) light?
- AIf the cable jacket is destroyed by UV, the cable will get moist and be damaged
- BUV excites nonlinear guided modes, causing intermodulation and harmonic emissions
- CUV mixes with the RF signal, causing fairly complex broadband interference
- DUV heats the cable and thereby increases its power loss
UV degrades the outer jacket; once it cracks, water enters and ruins the cable (A). UV is not an RF source and does not cause mixing, intermodulation, or heating of the cable (B/C/D are false).
US–China difference: US outdoor coax is also UV-rated (e.g., “direct burial”/”UV stable”).
Common pitfall: Imagining UV as an RF phenomenon causing interference.
Real on-air practice: Use UV-resistant coax or paint/tape it; sun-rotted jacket = water = failure.
相比填充有机介质的同轴电缆，空气介质同轴电缆的劣势是什么？
- A空气介质同轴电缆需要特别措施来防止湿气渗透
- B空气介质同轴电缆只能用于30MHz以下业余频段
- C空气介质同轴电缆的每百米损耗太大
- D空气介质同轴电缆不能在冰点以下工作
Compared with coaxial cable filled with organic dielectric, what is the disadvantage of air-dielectric coaxial cable?
- AAir-dielectric coaxial cable requires special measures to prevent moisture penetration
- BAir-dielectric coaxial cable can only be used below 30 MHz amateur bands
- CAir-dielectric coaxial cable has too much loss per 100 m
- DAir-dielectric coaxial cable cannot work below freezing point
Air dielectric gives very low loss but, being open to air, must be sealed against moisture ingress (A). It is not band-limited to 30 MHz, not high-loss, and works below freezing (B/C/D are wrong).
US–China difference: Air-dielectric hardline is used on US repeater sites for the same low-loss benefit, with weatherproofing.
Common pitfall: Thinking air-dielectric coax is only for HF.
Real on-air practice: A repeater’s heliax run is sealed at both ends to keep water out.
如果通过同轴电缆的信号频率升高，则同轴电缆的
- A传输损耗增加
- B反射功率升高
- C特性阻抗变高
- D输入驻波比变大
If the signal frequency passing through a coaxial cable rises, the coaxial cable’s:
- ATransmission loss increases
- BReflected power rises
- CCharacteristic impedance becomes higher
- DInput SWR becomes larger
Coax loss (especially dielectric loss) increases with frequency (A). Characteristic impedance is set by geometry and is essentially constant (C is wrong); reflected power and SWR depend on the load match, not on frequency alone (B, D are wrong).
US–China difference: Same frequency-dependent loss behavior in US coax charts.
Common pitfall: Thinking impedance or SWR changes simply because frequency rises.
Real on-air practice: A coax fine on 2 m may be far too lossy on 1.2 GHz.
以下给出了一些同等外径的馈线。其中哪一种在VHF/UHF频段损耗更低？
- A空气介质同轴硬电缆
- B独立屏蔽分组双绞线
- C50欧姆同轴软电缆
- D75欧姆同轴软电缆
Several feed lines of equal outer diameter are listed below. Which has lower loss in the VHF/UHF bands?
- AAir-dielectric rigid coaxial cable
- BIndividually shielded grouped twisted pair
- C50 Ω flexible coaxial cable
- D75 Ω flexible coaxial cable
Air-dielectric rigid coax has the lowest dielectric loss of these choices, so it has the lowest loss at VHF/UHF (A). Twisted pair and flexible coax have higher loss.
US–China difference: US repeater sites use air-dielectric “heliax” for the same low-loss reason.
Common pitfall: Assuming flexible coax is always the best because it is convenient.
Real on-air practice: Long UHF runs favor hardline despite its stiffness.
对于400MHz或更高频率的信号，应当优先选用的同轴电缆连接器是：
- AN型连接器
- BM型连接器
- CRS-213型连接器
- DDB-23型连接器
For signals at 400 MHz or higher, the coaxial connector that should be preferred is:
- AType N connector
- BType M connector
- CRS-213 connector
- DDB-23 connector
The Type N connector is designed for high frequencies (up to several GHz) with low loss and good impedance control, so it is preferred above 400 MHz (A). The M/RS-213/DB-23 choices are not the appropriate HF/VHF-UHF connectors for this purpose.
US–China difference: The US also uses Type N for 70 cm (432 MHz) and up; PL-259/SO-239 is fine only up to ~300 MHz.
Common pitfall: Using a UHF (PL-259) connector at 430 MHz+ where N is better.
Real on-air practice: Feed a 432 MHz yagi through N connectors for a clean match.
关于M型同轴电缆连接器，以下说法正确的是：
- A这种连接器广泛应用于HF和VHF通信系统
- B这种连接器使用了先进的螺纹式锁紧技术，防水防盗
- C这种连接器使用了卡式锁紧技术，便于快拔快插
- D这种连接器制造成本很高，通常用于微波通信系统
Which of the following statements about the Type M coaxial connector is correct?
- AThis connector is widely used in HF and VHF communication systems
- BThis connector uses advanced threaded locking technology, waterproof and anti-theft
- CThis connector uses bayonet locking technology, convenient for quick plug/unplug
- DThis connector is very costly to manufacture and is usually used in microwave communication systems
Per the question’s marked answer, the Type M connector is widely used in HF and VHF communication systems (A). The other descriptions — threaded/waterproof (B), bayonet quick-connect (C), and expensive microwave use (D) — are distractors for this item.
US–China difference: US hams more commonly meet the PL-259/SO-239 (“UHF”) and Type N; the “M” type is a China-exam-specific connector term.
Common pitfall: Confusing M-type with the bayonet BNC or threaded N connector.
Real on-air practice: Know the connector names from the exam bank; on the air you will mostly use PL-259/N.
关于垂直天线，以下说法正确的是：
- A该天线发射垂直极化波，电场与地面垂直
- B垂直天线是全向天线，其H面方向图是全向的
- C该天线发射垂直极化波，磁场与地面垂直
- D垂直天线是全向天线，其E面方向图是全向的
Which of the following statements about a vertical antenna is correct? (Choose all that apply.)
- AThis antenna radiates a vertically polarized wave, with the electric field perpendicular to the ground
- BA vertical antenna is an omnidirectional antenna, and its H-plane pattern is omnidirectional
- CThis antenna radiates a vertically polarized wave, with the magnetic field perpendicular to the ground
- DA vertical antenna is an omnidirectional antenna, and its E-plane pattern is omnidirectional
A vertical antenna radiates vertical polarization (E-field vertical, A correct) and is omnidirectional in azimuth — which is the H-plane — so the H-plane pattern is circular/omnidirectional (B correct). For vertical polarization the magnetic field is horizontal, not vertical (C wrong); the E-plane (vertical cut) is not omnidirectional (D wrong).
US–China difference: Same antenna theory in the US; vertical = H-plane omnidirectional.
Common pitfall: Mixing up which plane (E or H) is omnidirectional for a vertical.
Real on-air practice: Repeater antennas are usually vertical so any HT works regardless of heading.
关于水平极化偶极天线，以下描述正确的是：
- A通过该天线发射的电磁波，电场平行于地面
- B该天线水平面上的（E面）方向图呈“8”字展开
- C通过该天线发射的电磁波，电场垂直于地面
- D该天线垂直面上的（H面）方向图呈“8”字展开
Which of the following descriptions about a horizontally polarized dipole antenna is correct? (Choose all that apply.)
- AThe electromagnetic wave transmitted through this antenna has its electric field parallel to the ground
- BThe antenna’s horizontal-plane (E-plane) pattern is laid out as a “figure-8”
- CThe electromagnetic wave transmitted through this antenna has its electric field perpendicular to the ground
- DThe antenna’s vertical-plane (H-plane) pattern is laid out as a “figure-8”
A horizontal dipole radiates horizontal polarization (E-field parallel to ground, A correct). The plane containing the element is the E-plane; for a horizontal dipole that plane is horizontal, and its pattern is the figure-8 (B correct). C is wrong (that is vertical polarization); D swaps the E/H planes (the H-plane of a horizontal dipole is the vertical cut, which is omnidirectional).
US–China difference: Identical dipole theory in the US; horizontal dipoles give horizontal polarization.
Common pitfall: Swapping E-plane and H-plane labels for a horizontal dipole.
Real on-air practice: A horizontal dipole has nulls off its ends — point it broadside to your target.
甲、乙业余电台相距10千米，均使用1/2波长水平偶极天线进行UHF通联。现其中一方改用1/2波长垂直偶极天线，则改变前后的通信效果有什么不同？
- A通信效果变差
- B通信效果不变
- C通信效果变好
- D通信效果的变化不确定
Stations A and B are 10 km apart, both using 1/2-wavelength horizontal dipole antennas for UHF communication. Now one side switches to a 1/2-wavelength vertical dipole antenna. How does the communication effect differ before and after the change?
- ACommunication deteriorates
- BCommunication is unchanged
- CCommunication improves
- DThe change is uncertain
Initially both horizontal dipoles → matching polarization → good. Changing one to vertical creates cross-polarization (horizontal vs vertical), which loses roughly 20+ dB, so communication deteriorates (A).
US–China difference: Same polarization-matching rule applies to US UHF links.
Common pitfall: Forgetting that mismatched linear polarizations kill the signal.
Real on-air practice: Keep both ends’ dipoles horizontal (or both vertical) for a weak-signal UHF contact.
甲、乙业余电台相距10千米，分别使用1/2波长水平和垂直偶极天线进行UHF通联。现双方都改用1/2波长垂直偶极天线，则改变前后的通信效果有什么不同？
- A通信效果变好
- B通信效果不变
- C通信效果变差
- D通信效果的变化不确定
Stations A and B are 10 km apart, using 1/2-wavelength horizontal and vertical dipole antennas respectively for UHF. Now both switch to 1/2-wavelength vertical dipole antennas. How does the effect differ?
- ACommunication improves
- BCommunication is unchanged
- CCommunication deteriorates
- DThe change is uncertain
Initially cross-polarized (one H, one V) → poor. After both become vertical → matching polarization → improves (A).
US–China difference: Same principle.
Common pitfall: Overthinking; just match the polarizations at both ends.
Real on-air practice: Two verticals on 432 MHz talk fine where one vertical + one horizontal struggled.
甲、乙业余电台相距10千米，分别使用1/2波长水平和垂直偶极天线进行UHF通联。现双方都改用1/2波长水平偶极天线，则改变前后的通信效果有什么不同？
- A通信效果变好
- B通信效果不变
- C通信效果变差
- D通信效果的变化不确定
Stations A and B are 10 km apart, using 1/2-wavelength horizontal and vertical dipoles respectively for UHF. Now both switch to 1/2-wavelength horizontal dipole antennas. How does the effect differ?
- ACommunication improves
- BCommunication is unchanged
- CCommunication deteriorates
- DThe change is uncertain
Initially cross-polarized → poor. After both become horizontal → matching polarization → improves (A).
US–China difference: Same principle.
Common pitfall: None significant here; matching polarization always helps.
Real on-air practice: Align both dipoles the same way and the link comes up.
甲、乙业余电台相距10千米，分别使用左旋圆极化和右旋圆极化天线彼此对指进行UHF通联。现双方都改用左旋圆极化天线，则改变前后的通信效果有什么不同？
- A通信效果变好
- B通信效果不变
- C通信效果变差
- D通信效果的变化不确定
Stations A and B are 10 km apart, using left-hand and right-hand circularly polarized antennas pointed at each other for UHF. Now both switch to left-hand circularly polarized antennas. How does the effect differ?
- ACommunication improves
- BCommunication is unchanged
- CCommunication deteriorates
- DThe change is uncertain
Initially opposite circular polarizations (LHCP vs RHCP) → near-complete rejection, very poor. After both become LHCP → matched → improves (A).
US–China difference: Same; opposite circular polarizations are essentially orthogonal.
Common pitfall: Thinking any “circular” matches any other circular — sense matters.
Real on-air practice: Satellite work uses one sense; a crossed-sense partner would be inaudible.
甲、乙业余电台相距10千米，分别使用左旋圆极化和右旋圆极化天线彼此对指进行UHF通联。现双方都改用右旋圆极化天线，则改变前后的通信效果有什么不同？
- A通信效果变好
- B通信效果不变
- C通信效果变差
- D通信效果的变化不确定
Stations A and B are 10 km apart, using left-hand and right-hand circularly polarized antennas pointed at each other for UHF. Now both switch to right-hand circularly polarized antennas. How does the effect differ?
- ACommunication improves
- BCommunication is unchanged
- CCommunication deteriorates
- DThe change is uncertain
Same as U0476: initially mismatched opposite circular polarizations → poor; both RHCP → matched → improves (A).
US–China difference: Same principle.
Common pitfall: Picking “unchanged” by assuming both were already circular.
Real on-air practice: Match the sense at both ends and the weak link jumps in strength.
甲、乙业余电台相距10千米，分别使用左旋圆极化和半波长水平偶极天线彼此对指进行UHF通联。现乙台改用半波长垂直极化天线，则改变前后的通信效果有什么不同？
- A通信效果不变
- B通信效果变差
- C通信效果变好
- D通信效果的变化不确定
Stations A and B are 10 km apart, using left-hand circular polarization (A) and a half-wave horizontal dipole (B) pointed at each other for UHF. Now station B switches to a half-wave vertically polarized antenna. How does the effect differ?
- ACommunication is unchanged
- BCommunication deteriorates
- CCommunication improves
- DThe change is uncertain
A linear polarization (horizontal or vertical) can be decomposed into equal left- and right-hand circular components. Thus a circularly polarized antenna receiving a linear signal (or vice versa) always captures half the power (−3 dB) regardless of the linear orientation. Changing station B from a horizontal to a vertical linear dipole still yields the same −3 dB, so the effect is unchanged (A).
US–China difference: Same linear↔circular −3 dB rule used in US satellite/EME planning.
Common pitfall: Thinking switching the linear dipole’s orientation changes the result with a circular partner.
Real on-air practice: A circularly polarized satellite antenna hears your linearly polarized HT at a fixed −3 dB penalty.
甲、乙业余电台相距10千米，分别使用左旋圆极化和半波长水平偶极天线彼此对指进行UHF通联。现甲台改用右旋圆极化天线，则改变前后的通信效果有什么不同？
- A通信效果不变
- B通信效果变差
- C通信效果变好
- D通信效果的变化不确定
Stations A and B are 10 km apart, using left-hand circular polarization (A) and a half-wave horizontal dipole (B) pointed at each other for UHF. Now station A switches to a right-hand circularly polarized antenna. How does the effect differ?
- ACommunication is unchanged
- BCommunication deteriorates
- CCommunication improves
- DThe change is uncertain
A linear polarization (the dipole) contains equal LHCP and RHCP parts, so a circularly polarized antenna — whether LHCP or RHCP — captures the same half-power regardless of its sense. Switching A from LHCP to RHCP while its partner is a linear dipole yields an unchanged result (A).
US–China difference: Same rule.
Common pitfall: Assuming the circular sense change matters against a linear partner.
Real on-air practice: With a linear station, your circular sense choice makes no difference to signal strength.
甲、乙业余电台相距10千米，分别使用左旋圆极化和半波长水平偶极天线彼此对指进行UHF通联。现乙台改用右旋圆极化天线，则改变前后的通信效果有什么不同？
- A通信效果变差
- B通信效果变好
- C通信效果不变
- D通信效果的变化不确定
Stations A and B are 10 km apart, using left-hand circular polarization (A) and a half-wave horizontal dipole (B) pointed at each other for UHF. Now station B switches to a right-hand circularly polarized antenna. How does the effect differ?
- ACommunication deteriorates
- BCommunication improves
- CCommunication is unchanged
- DThe change is uncertain
Initially B is a linear dipole, which contains both circular components, so it couples to A’s LHCP at −3 dB. After B becomes RHCP, it is opposite to A’s LHCP → near-total rejection → much worse (A).
US–China difference: Same cross-sense rejection in the US.
Common pitfall: Treating the dipole as if it had a fixed circular sense.
Real on-air practice: A linear-to-circular link is −3 dB; circular-to-opposite-circular is essentially dead.
甲、乙业余电台相距10千米，分别使用左旋圆极化和半波长水平偶极天线彼此对指进行UHF通联。现乙台改用左旋圆极化天线，则改变前后的通信效果有什么不同？
- A通信效果变好
- B通信效果变差
- C通信效果不变
- D通信效果的变化不确定
Stations A and B are 10 km apart, using left-hand circular polarization (A) and a half-wave horizontal dipole (B) pointed at each other for UHF. Now station B switches to a left-hand circularly polarized antenna. How does the effect differ?
- ACommunication improves
- BCommunication deteriorates
- CCommunication is unchanged
- DThe change is uncertain
Initially B is a linear dipole → −3 dB capture by A’s LHCP. After B becomes LHCP matching A, the link is fully matched → improves (A).
US–China difference: Same principle.
Common pitfall: Forgetting the −3 dB linear-to-circular baseline.
Real on-air practice: Match circular senses for the strongest satellite/EME signal.
甲、乙业余电台相距10千米，分别使用左旋圆极化和右旋圆极化天线彼此对指进行UHF通联。现双方均改用半波长水平偶极天线，则改变前后的通信效果有什么不同？
- A通信效果变好
- B通信效果不变
- C通信效果变差
- D通信效果的变化不确定
Stations A and B are 10 km apart, using left-hand and right-hand circularly polarized antennas pointed at each other for UHF. Now both switch to half-wave horizontal dipole antennas. How does the effect differ?
- ACommunication improves
- BCommunication is unchanged
- CCommunication deteriorates
- DThe change is uncertain
Initially opposite circular polarizations → near-total rejection (very poor). After both become horizontal dipoles (matched linear polarization) → big improvement (A).
US–China difference: Same.
Common pitfall: Missing that the starting circular pair was essentially orthogonal.
Real on-air practice: Two crossed-sense circular antennas hear almost nothing; two dipoles hear plenty.
假设接收和发射天线均使用半波长偶极天线，则在地面台站间的近距离通联中，接收和发射天线的最佳极化方式应当安排为：
- A接收和发射天线均位于垂直于两台站连线的平面内，极化保持一致
- B接收和发射天线均位于垂直于两台站连线的平面内，极化彼此正交
- C接收和发射天线的极化应当平行于两台站之间的连线
- D发射天线垂直极化，接收天线的极化应当平行于两台站之间的连线
Assume both receiving and transmitting antennas use half-wave dipoles. For short-distance communication between ground stations, the best polarization arrangement for the receiving and transmitting antennas should be:
- ABoth receiving and transmitting antennas lie in the plane perpendicular to the line connecting the two stations, with polarizations kept consistent
- BBoth receiving and transmitting antennas lie in the plane perpendicular to the line connecting the two stations, with polarizations orthogonal to each other
- CThe polarizations of the receiving and transmitting antennas should be parallel to the line connecting the two stations
- DThe transmitting antenna is vertically polarized, and the receiving antenna’s polarization should be parallel to the line connecting the two stations
For two ground stations the wave travels horizontally; the E-field must be perpendicular to the propagation direction (i.e., in the plane normal to the link line), and both ends must share the same polarization for best coupling (A). Orthogonal polarizations (B) or aligning the E-field along the link line (C/D) give poor coupling.
US–China difference: Same polarization-alignment rule for US ground-wave VHF/UHF.
Common pitfall: Pointing the dipole elements along the path instead of broadside.
Real on-air practice: Two horizontal dipoles, both broadside to each other, give the best weak-signal path.
右旋极化波是指在垂直于传播方向的任意平面上，沿传播方向观察时，电场矢量为随时间向右（顺时针）旋转的椭圆或圆极化波。如果地面上某业余电台在观测业余卫星时发现从卫星到达该台的无线电波的电场是顺时针旋转的，则该信号的极化方式为：
- A左旋椭圆极化或圆极化
- B右旋椭圆极化或圆极化
- C垂直极化
- D水平极化
A right-hand polarized wave means, on any plane perpendicular to the direction of propagation, when viewed along the direction of propagation the electric-field vector rotates clockwise (to the right) with time — an elliptically or circularly polarized wave. If a ground amateur station observing an amateur satellite finds that the electric field of the radio wave arriving from the satellite rotates clockwise, then the polarization of that signal is:
- ALeft-hand elliptical or circular polarization
- BRight-hand elliptical or circular polarization
- CVertical polarization
- DHorizontal polarization
This is the classic “viewing from the opposite end” trap. RHCP is defined as clockwise when viewed along the propagation direction. The ground station views the arriving wave from the receiver’s side — i.e., opposite to the propagation direction (the wave travels downward from satellite to ground). Clockwise as seen by the receiver equals counter-clockwise along propagation, which is left-hand. So the signal is left-hand (LHCP/LHEP) (A).
US–China difference: Same IEEE polarization convention in the US; the “which way are you looking” subtlety trips up everyone.
Common pitfall: Concluding “clockwise = right-hand” without checking the viewing direction.
Real on-air practice: When a satellite passes overhead, the apparent sense flips — plan your antenna sense accordingly.
在视距通联中，已知发射天线为指向接收点的左旋圆极化天线，接收天线的最佳极化方式为：
- A指向发射点的左旋圆极化
- B指向发射点的右旋圆极化
- C垂直极化
- D水平极化
In line-of-sight communication, given the transmitting antenna is a left-hand circularly polarized antenna pointing at the receiving point, the best polarization for the receiving antenna is:
- ALeft-hand circular polarization pointing at the transmitting point
- BRight-hand circular polarization pointing at the transmitting point
- CVertical polarization
- DHorizontal polarization
For best reception the receiving antenna should match the transmitting polarization: same sense (left-hand) circular, pointed back at the transmitter (A). Opposite sense (B) rejects the signal; fixed linear (C/D) loses 3 dB.
US–China difference: Same “match the sense” rule for US circular-polarized links.
Common pitfall: Picking right-hand, forgetting the match must be same-sense.
Real on-air practice: Point your LHCP yagi back at an LHCP station for max signal.
某卫星下行链路采用右旋圆极化天线，从北向南飞行，天线始终指向地球的南极。如果地面上某业余电台采用圆极化天线自动跟踪该卫星，则该台所用天线的最佳极化方式应当为：
- A卫星过顶前为右旋圆极化，过顶后为左旋圆极化
- B卫星过顶后为右旋圆极化，过顶前为左旋圆极化
- C最佳方向始终为右旋圆极化
- D最佳方向始终为左旋圆极化
A satellite’s downlink uses a right-hand circularly polarized antenna, flies from north to south, and the antenna always points at the Earth’s south pole. If a ground amateur station uses a circularly polarized antenna to auto-track the satellite, the best polarization for that station’s antenna should be:
- ARight-hand circular polarization before the satellite passes overhead, left-hand circular polarization after it passes overhead
- BLeft-hand circular polarization before the satellite passes overhead, right-hand circular polarization after it passes overhead
- CAlways right-hand circular polarization is best
- DAlways left-hand circular polarization is best
The satellite’s antenna points south (downward toward Earth’s south pole). As the satellite travels north→south and crosses overhead, the direction from satellite to the ground station flips (the wave arrives from the north before culmination, from the south after). Viewed along propagation, the apparent sense flips at culmination, so the ground station must switch from RHCP to LHCP (A). This is the same “viewing direction” principle as U0484.
US–China difference: US satellite operators also flip circular sense at culmination (e.g., AO-91, SO-50).
Common pitfall: Assuming one fixed sense works all pass.
Real on-air practice: Set your rotor/polarization to swap sense as the bird goes overhead.
已知某卫星下行信号的发射天线是指向地面的偶极天线。由于卫星不断旋转，地面台站所收电波的极化方向就会不断变化。为了不至极化问题致使接收中断，接收天线可以是：
- A指向卫星的右旋或左旋圆极化天线
- B垂直极化天线
- C水平极化天线
- D极化方向平行于卫星与地面电台之间连线的天线
It is known that a satellite’s downlink transmitting antenna is a dipole pointing at the ground. Because the satellite keeps rotating, the polarization direction of the wave received by the ground station keeps changing. To avoid polarization issues interrupting reception, the receiving antenna can be:
- AA right-hand or left-hand circularly polarized antenna pointing at the satellite
- BA vertically polarized antenna
- CA horizontally polarized antenna
- DAn antenna whose polarization direction is parallel to the line between the satellite and the ground station
A circularly polarized receiving antenna captures a linearly polarized (rotating) wave regardless of its instantaneous orientation (always ~−3 dB), so it will not drop out as the satellite tumbles (A). Fixed linear polarizations (B/C/D) would fade as the orientation changes relative to the antenna.
US–China difference: US hams use circular-polarized antennas for spinning-satellite and EME work for this reason.
Common pitfall: Thinking a fixed vertical/horizontal antenna will track a tumbling satellite.
Real on-air practice: A helical (circular) antenna hears a tumbling cubesat steadily.
某业余电台使用半波垂直偶极天线通联时，对方所收信号的强度为S4。现发射功率不变，发信方改用增益为8.15dBi的八木天线（最大辐射方向和极化均不变），则对方所收信号的强度变为：【提示：收信机信号强度指示从S1至S9每档增加6dB】
- AS5
- BS6
- CS7
- DS8
An amateur station using a half-wave vertical dipole for a contact receives an S4 signal strength at the other end. Now, with transmit power unchanged, the transmitting station switches to a Yagi antenna with 8.15 dBi gain (maximum radiation direction and polarization unchanged). What does the received signal strength at the other end become? [Hint: the receiver’s S-meter increases by 6 dB per step from S1 to S9]
- AS5
- BS6
- CS7
- DS8
A half-wave vertical dipole has a gain of 2.15 dBi. The Yagi is 8.15 dBi, so the improvement is 8.15 − 2.15 = 6 dB, which is exactly one S-unit. S4 + 1 = S5 (A).
US–China difference: S-meter calibration (6 dB/S-unit) is the same convention used by US radios.
Common pitfall: Forgetting a dipole is 2.15 dBi, not 0 dBi.
Real on-air practice: Swapping a vertical for a yagi can lift a marginal S4 to a solid S5.
某业余电台使用半波长垂直偶极天线发射时，对方所收信号的强度为S4。现发射功率不变，发信方改用增益为12dBd的八木天线（最大辐射方向和极化均不变），则对方所收信号的强度变为：【提示：收信机信号强度指示从S1至S9每档增加6dB】
- AS6
- BS5
- CS7
- DS8
An amateur station transmitting with a half-wave vertical dipole yields an S4 received signal at the other end. Now, power unchanged, the transmitting station switches to a Yagi with 12 dBd gain (direction and polarization unchanged). What does the received strength become? [Hint: S-meter +6 dB per step]
- AS6
- BS5
- CS7
- DS8
12 dBd = 12 + 2.15 = 14.15 dBi. A dipole is 2.15 dBi, so the improvement is 12 dB = two S-units. S4 + 2 = S6 (A).
US–China difference: Same dBd→dBi and S-unit math.
Common pitfall: Treating 12 dBd as if it were 12 dBi (you’d then get only ~10 dB ≈ S4+1.7).
Real on-air practice: A big 12 dBd yagi can lift S4 to S6, often the difference between no contact and a clean one.
两位业余爱好者使用半波长垂直偶极天线相互通联，双方所收信号的强度均为S4。现双方发射功率不变，都改用增益为8.15dBi的八木天线（最大辐射方向和极化均不变）再次联络，则双方信号的强度变为：【提示：收信机信号强度指示S1至S9每档增加6dB】
- AS6
- BS4
- CS5
- DS7
Two amateurs use half-wave vertical dipoles to contact each other; each receives the other’s signal at S4. Now, with transmit power unchanged, both switch to Yagis with 8.15 dBi gain (direction and polarization unchanged) and make contact again. What do both signals’ strengths become? [Hint: S-meter +6 dB per step]
- AS6
- BS4
- CS5
- DS7
Each end gains 6 dB (one S-unit) from its dipole (2.15 dBi) to the 8.15 dBi Yagi. Both link ends improve by one S-unit, so each signal goes from S4 to S4 + 1 + 1 = S6 (A).
US–China difference: Same two-ended gain reasoning.
Common pitfall: Counting the gain only once instead of at both stations.
Real on-air practice: Both stations upgrading to yagis can turn a scratchy S4/S4 into a solid S6/S6.
即便是在辽阔的平原或广袤的戈壁，我们所收本地VHF/UHF信号的强度也会伴随设备的移动而发生周期性的变化。主要原因是：
- A来自直射和地面反射等多个路径的无线电波相互干涉，相消或相长（多径效应）
- B发信和收信地点间的气流导致电波传播路径弯曲，发生频率漂移（多普勒效应）
- C无论收信发信，地面各处的电导率不尽相同会导致设备移动时的接地电阻变化
- D发信过程中，设备与大地间分布电容的改变导致天线失谐，发射功率随之改变
Even on an open plain or vast desert, the strength of locally received VHF/UHF signals changes periodically as the equipment moves. The main reason is:
- ARadio waves from multiple paths such as direct and ground-reflected rays interfere with each other, canceling or reinforcing (multipath effect)
- BAirflow between transmitting and receiving locations bends the propagation path, causing frequency drift (Doppler effect)
- CRegardless of receiving or transmitting, differing ground conductivity everywhere causes the grounding resistance to change as the equipment moves
- DDuring transmission, changes in the distributed capacitance between the equipment and the ground detune the antenna, changing the transmit power
As you move, the relative phase of the direct and reflected waves shifts, producing constructive/destructive interference — multipath fading (A). Doppler from walking is tiny; B/C/D are not the cause of the periodic signal swing.
US–China difference: Multipath fading is the same phenomenon US hams see on 2 m mobile.
Common pitfall: Blaming Doppler (which is negligible at walking speed on VHF).
Real on-air practice: Take a few steps and the 2 m signal may swing 10–20 dB from nulls.
在VHF/UHF频段通联时的一个现象，如果远方电台给出的信号报告很差，则仅需移动几步或将工作频率改变数十千赫就可能显著改善通信效果。这是因为：
- A多径传播。经不同路径达到天线的电波存在相位和幅度差异，相互干涉，相消或相长
- B发射机与接收机之间的距离，以及工作频率的变化都会显著改变路径损耗
- C大气扰动影响
- D地磁活动影响
A phenomenon in VHF/UHF contacts: if a distant station gives a poor signal report, merely moving a few steps or changing the operating frequency by tens of kHz can significantly improve communication. This is because:
- AMultipath propagation. Waves arriving at the antenna via different paths have phase and amplitude differences and interfere, canceling or reinforcing
- BThe distance between transmitter and receiver, and changes in operating frequency, both significantly change path loss
- CAtmospheric disturbance effects
- DGeomagnetic activity effects
Small position or frequency changes alter the multipath phase combination, possibly turning destructive interference into constructive (A). Path loss does not change much over a few steps (B); atmospheric and geomagnetic effects are not the cause here (C/D).
US–China difference: US hams also “move a few feet” or “try another freq” to beat a VHF multipath null.
Common pitfall: Attributing the improvement to path-loss change rather than multipath phase.
Real on-air practice: A weak 440 MHz contact often pops up after you shift 25 kHz or step aside.
多径传播对UHF或VHF波段数据通信的影响是：
- A可能使误码率上升
- B如果是FM通联，则影响微不足道，不可察觉
- C随着传播路径的增加，数据通信速率线性减小
- D随着传播路径的增加，数据通信速率线性增加
The effect of multipath propagation on UHF or VHF data communication is:
- AIt may raise the bit error rate (BER)
- BIf it is FM communication, the effect is negligible and imperceptible
- CAs the number of propagation paths increases, the data communication rate decreases linearly
- DAs the number of propagation paths increases, the data communication rate increases linearly
Multipath causes delay spread and fading that can increase the BER of digital modes (A). B is too strong — multipath can still affect FM/data; C/D’s linear rate claims are false.
US–China difference: Same multipath/BER issue on US VHF/UHF digital modes (APRS, D-STAR, DMR).
Common pitfall: Thinking more paths automatically mean a faster or slower fixed-linear rate.
Real on-air practice: A flaky 1200-baud APRS digipeat in town is often multipath between buildings.
使用VSB方式进行ATV通信时，即使信号相对较强，有时所收图像的边缘也有重影。这是因为：
- A多径传播。来自不同路径的信号到达接收天线的时延不同，造成重影
- B发射天线的VSWR过高。如果信号在馈线中多次往返于发射机和天线，会造成重影
- C天线的极化配置出错。极化不同的信号同时到达天线，导致重影
- D遭遇了重放干扰。或许是某中继台也转发了这个信号，其到达接收天线，导致重影
When using VSB (vestigial sideband) for ATV (amateur television) communication, even when the signal is relatively strong, the edges of the received image sometimes show ghosts. This is because: (Choose all that apply.)
- AMultipath propagation. Signals from different paths arrive at the receiving antenna with different delays, causing ghosts
- BThe transmitting antenna’s VSWR is too high. If the signal bounces repeatedly between transmitter and antenna in the feed line, it causes ghosts
- CThe antenna polarization is misconfigured. Signals of different polarizations arrive at the antenna simultaneously, causing ghosts
- DIt encountered replay interference. Perhaps a repeater also retransmitted this signal, and its arrival at the receiving antenna causes ghosts
Ghosting in VSB/ATV mainly comes from multipath: reflected paths arrive delayed and overlay a shifted copy of the picture (A). Additionally, a high VSWR at the transmit antenna makes part of the signal reflect back and forth along the feed line, producing a delayed echo that also appears as a ghost (B). Polarization errors (C) and repeater replay (D) are not the causes marked for this item.
US–China difference: US ATV (now mostly DATV) hams see the same multipath ghosts on 70 cm analog TV.
Common pitfall: Assuming ghosts are always a polarization problem.
Real on-air practice: A strong local ATV signal still ghosts if a building reflects a delayed copy into your antenna.
决定超短波视距传播距离极限的主要因素是：
- A发射天线和接收天线距地面的相对高度
- B发射天线和接收天线距海平面的绝对高度
- C发射天线和接收天线的挂高波长比，即，离地高度除以波长
- D发射天线和接收天线的增益
The main factor that determines the maximum range of ultra-short-wave (VHF/UHF) line-of-sight propagation is:
- Athe relative heights of the transmitting and receiving antennas above the ground
- Bthe absolute heights of the transmitting and receiving antennas above sea level
- Cthe height-to-wavelength ratio of the transmitting and receiving antennas (height above ground divided by wavelength)
- Dthe gain of the transmitting and receiving antennas
The range of line-of-sight (视线传播) propagation of ultra-short waves (VHF/UHF) is limited by the radio horizon, which depends mainly on how high the antennas are above the local ground (the relative height), not on their absolute altitude above sea level. A higher antenna above ground sees farther over the Earth’s curvature. Options B, C and D are secondary or irrelevant: absolute sea-level height matters far less than local terrain clearance, the height-to-wavelength ratio does not set the horizon limit, and antenna gain improves signal margin but not the geometric horizon.
US–China difference: N/A — the radio-horizon concept is identical worldwide; both FCC and CRAC exams treat antenna height above ground as the dominant factor for VHF/UHF line-of-sight range.
Common pitfall: Confusing “relative height above ground” with “absolute height above sea level”; a station on a high plateau is not automatically farther-seeing if local terrain still blocks the path. Also do not pick the height-to-wavelength ratio (C), which sounds technical but is not the horizon determinant.
Real on-air practice: Hams place VHF/UHF antennas as high as possible above local rooftops/trees to extend simplex and repeater coverage — the classic “height is might” rule for 2 m and 70 cm work.
有时，相隔数百千米的业余电台可以实现VHF/UHF超视距直接联络。可能的原因是：
- A信号的传播路径中出现了大气波导现象
- B有飞行器在空中反射了电波
- C降雨增加了大地电导率，增强了电波传播
- D每当冬季，植被的减少都有利于电波传播
Sometimes amateur stations hundreds of kilometres apart can make VHF/UHF beyond-line-of-sight direct contacts. The possible reason is:
- Aan atmospheric ducting phenomenon appeared along the propagation path
- Ban aircraft reflected the radio waves in the air
- Crainfall increased the earth’s conductivity and enhanced wave propagation
- Devery winter, reduced vegetation favours wave propagation
Beyond-line-of-sight (超视距) VHF/UHF contacts over hundreds of km are most commonly caused by tropospheric ducting (大气波导), where a temperature inversion traps radio waves in a waveguide-like layer that follows the Earth’s curvature. Aircraft reflection (B) is rare and brief; rainfall (C) generally attenuates rather than enhances VHF/UHF; seasonal vegetation loss (D) has negligible effect at these bands. Therefore A is the standard correct explanation.
US–China difference: N/A — tropospheric ducting is a global propagation mechanism taught similarly in both FCC and CRAC materials.
Common pitfall: Mistaking aircraft reflection (B) or meteor scatter for the “hundreds of km” case; ducting is the dominant cause for sustained VHF/UHF over-horizon contacts at this range. Also note ducting is tropospheric, not ionospheric.
Real on-air practice: During temperature-inversion evenings, 2 m and 70 cm operators log unexpectedly long DX; spotting networks and propagation beacons help identify ducting openings.
有时，我们可以在6米或2米业余波段中收到上千千米外的”超视距传播”信号。这与下列哪种现象密切相关？
- A突发E层的传播
- B流星余迹反向散射
- CD层的吸收所致
- D灰线传播
Sometimes we can receive “beyond-line-of-sight propagation” signals from over a thousand kilometres away on the 6 m or 2 m amateur bands. This is closely related to which of the following phenomena?
- Asporadic-E (sporadic E-layer) propagation
- Bmeteor-scatter backscatter
- Cabsorption by the D layer
- Dgray-line propagation
Sporadic E (突发E层) is the dominant cause of 6 m and 2 m signals reaching a thousand km or more: dense patches of ionized E-layer clouds reflect VHF signals far beyond the horizon, often with strong signals. Meteor scatter (B) gives only very brief, weak bursts and is not the main “regularly received” thousand-km mechanism; D-layer absorption (C) weakens signals rather than enabling DX; gray-line (D) is mainly an HF dawn/dusk effect. Hence A is correct.
US–China difference: N/A — sporadic-E propagation on 6 m and 2 m is a worldwide phenomenon and is described the same way in FCC and CRAC study materials.
Common pitfall: Confusing meteor scatter (B) with sporadic E; meteor scatter needs digital/burst modes and gives short pings, whereas the question describes “received” strong signals over long distances — that is sporadic E.
Real on-air practice: During summer Es season, 6 m operators work stations across continents using SSB and FT8; a brief “ping” on 2 m may instead be meteor scatter.
是什么导致了对流层的大气波导现象？
- A大气高空逆温
- B太阳黑子和/或太阳耀斑
- C飓风或龙卷风所致的上升气流
- D雷暴时大量闪电所产生的等离子体
What causes tropospheric atmospheric ducting?
- Aa temperature inversion in the upper atmosphere
- Bsunspots and/or solar flares
- Cupdrafts caused by hurricanes or tornadoes
- Dplasma produced by abundant lightning during thunderstorms
Tropospheric ducting (大气波导) is created when a temperature inversion (逆温) — a layer of warm air above cooler air — forms in the lower atmosphere. This refractive-index gradient bends VHF/UHF rays downward, confining them in a duct. Sunspots/flares (B) affect HF via the ionosphere, not tropospheric ducts; hurricanes (C) and lightning plasma (D) are not the cause of normal ducting. Thus A is correct.
US–China difference: N/A — the physics of tropospheric ducting from temperature inversions is identical everywhere.
Common pitfall: Linking ducting to solar activity (B); that affects ionospheric, not tropospheric, propagation. Ducting is a weather/lower-atmosphere effect.
Real on-air practice: Ducting often appears over calm, clear nights with temperature inversions; coastal VHF operators see signals bending far beyond the horizon.
如果你收到了一个上千千米外的VHF信号，最可能的原因是：
- A信号经电离层的突发E层反射而来
- B信号由微波接力电台合力QSP过来
- C信号被附近的雷雨区反射而来
- D信号经宇宙射线的电离路径传导过来
If you receive a VHF signal from over a thousand kilometres away, the most likely reason is:
- Athe signal was reflected by the sporadic E layer of the ionosphere
- Bthe signal was relayed through by microwave relay stations
- Cthe signal was reflected by a nearby thunderstorm area
- Dthe signal was conducted through an ionization path of cosmic rays
For a VHF signal to travel a thousand km, the usual mechanism is reflection from the sporadic E layer (突发E层) of the ionosphere, which can return 6 m/2 m signals over very long distances. Microwave relay (B), thunderstorm reflection (C) and cosmic-ray paths (D) are not realistic normal mechanisms for such reception. So A is correct.
US–China difference: N/A — VHF DX at 1000+ km is attributed to sporadic E in both FCC and CRAC contexts.
Common pitfall: Over-thinking exotic mechanisms (D). The exam expects the standard answer: sporadic-E ionospheric reflection.
Real on-air practice: A 144 MHz SSB contact over 1500 km during an Es opening is a classic example; the signal appears suddenly and strongly.
有时，VHF/UHF业余波段中可能出现远达500千米的”超视距传播”信号。这与下列哪种现象密切相关？
- A对流层散射
- BD层折射
- CF2层折射
- D法拉第旋转
Sometimes “beyond-line-of-sight propagation” signals up to 500 km away may appear in VHF/UHF amateur bands. This is closely related to which of the following phenomena?
- Atropospheric scattering
- BD-layer refraction
- CF2-layer refraction
- DFaraday rotation
Tropospheric scattering (对流层散射) — scattering of VHF/UHF waves by inhomogeneities in the troposphere — routinely yields contacts up to several hundred km (around 500 km here). D-layer (B) absorbs rather than refracts VHF usefully; F2 refraction (C) is an HF mechanism; Faraday rotation (D) is a polarization effect on satellite/satellite paths, not a 500 km terrestrial DX cause. Therefore A is correct.
US–China difference: N/A — tropospheric scatter is a recognized VHF propagation mode globally.
Common pitfall: Assigning the 500 km case to ionospheric F2 (C); F2 supports HF, not VHF/UHF, over-the-horizon work. The mid-range VHF DX answer is tropospheric scatter/ducting.
Real on-air practice: Troposcatter links using narrowband digital modes let hams bridge 300–800 km gaps where no repeater exists.
💬 Have questions about this topic, or FCC / CRAC exam preparation?
对本篇内容或 FCC / CRAC 备考有疑问？
本手册仅供业余无线电爱好者学习交流，题库原题版权归 CRAC（中国无线电协会业余无线电分会）所有，英文翻译由 BG7BAG 编译，转载请注明出处。
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