What is a beam antenna?
AnswerAn antenna that concentrates signals in one direction
A beam antenna is directional: it concentrates more of its transmitted and received energy in one direction instead of distributing it equally in all directions.
RF PREP // FCC AMATEUR RADIO
T9 · Antennas and Feed Lines
Technician · correct answers only, in question-pool order.
Which of the following describes a type of antenna loading?
AnswerElectrically lengthening by inserting inductors in radiating elements
Loading coils add inductance to an antenna and make a physically short radiator behave electrically like a longer one.
How is the polarization of an antenna described?
AnswerBy the orientation of the electric field
Antenna polarization is defined by the orientation of the radiated electric field. A vertical antenna produces primarily vertical polarization, while a horizontal antenna produces horizontal polarization.
What is a disadvantage of a handheld radio transceiver’s short flexible antenna compared to a full-sized quarter-wave antenna?
AnswerIt has low efficiency
A short flexible handheld antenna is much shorter than a full-sized quarter-wave radiator, so it generally converts less transmitter power into radiated RF.
Which of the following increases the resonant frequency of a dipole antenna?
AnswerShortening it
A resonant dipole becomes resonant at a higher frequency when its physical length is shortened, because resonant length is inversely related to frequency.
Which of the following types of antennas offers the greatest gain?
AnswerYagi
A Yagi uses multiple elements to concentrate energy strongly in one direction, giving it more directional gain than the other listed antenna types.
What is a potential drawback of using a handheld VHF transceiver inside a vehicle that lacks an externally mounted antenna?
AnswerSignal strength is reduced due to the shielding effect of the vehicle
The metal body of a vehicle partially shields RF from a handheld antenna used inside the cabin, reducing transmitted and received signal strength.
Why is a 19-inch-long vertical antenna often used on 2 meters?
AnswerIt is a resonant quarter-wave
A quarter wavelength on the 2-meter band is roughly 19 inches, making a 19-inch vertical a practical resonant quarter-wave antenna.
What is an advantage of a 5/8-wavelength whip antenna for VHF or UHF mobile service compared to a 1/4-wave antenna?
AnswerIt has more gain
A 5/8-wave vertical reshapes the radiation pattern to place more energy near the horizon than a simple quarter-wave vertical, producing useful gain for terrestrial mobile work.
In which direction does a half-wave dipole antenna radiate the strongest signal?
AnswerBroadside to the antenna
A half-wave dipole has its strongest radiation broadside to the wire and much weaker radiation off the ends.
What is antenna gain?
AnswerThe increase in signal strength in a specified direction compared to a reference antenna
Antenna gain describes how strongly an antenna concentrates radiation in a specified direction compared with a reference antenna.
Which of the following connectors should be carefully taped for weather protection when used outdoors?
AnswerPL-259, BNC, and Type N connectors should all be carefully weatherproofed when used outdoors.
Outdoor coax connectors need protection from moisture regardless of connector style. Water intrusion causes corrosion and can greatly increase feed-line loss.
What is the most common impedance of coaxial cables used in amateur radio?
Answer50 ohms
Most amateur transmitters, feed lines, and antenna systems are designed around a nominal 50-ohm impedance.
Why is coaxial cable the most common feed line for amateur radio antenna systems?
AnswerIt is easy to use and requires few special installation considerations
Coax is popular because it is mechanically convenient, easy to route, relatively tolerant of nearby objects, and requires fewer special installation precautions than open-wire line.
What is the major function of an antenna tuner (antenna coupler)?
AnswerIt matches the antenna system impedance to the transceiver's output impedance
An antenna tuner transforms the impedance presented by the antenna system so the transceiver sees a load closer to its intended output impedance, usually 50 ohms.
What happens as the frequency of a signal in coaxial cable is increased?
AnswerThe loss increases
Coaxial cable loss rises as frequency increases because conductor and dielectric losses become greater at higher RF frequencies.
Which of the following connector types is most suitable as an RF connector for frequencies above 400 MHz?
AnswerType N
Type N connectors maintain good RF characteristics into the UHF and microwave range and are a better choice above 400 MHz than a PL-259.
Which of the following is true of PL-259 type coax connectors?
AnswerThey are commonly used at HF and VHF frequencies
PL-259 connectors are widely used in amateur stations at HF and VHF, though they are not the preferred connector for microwave work and are not inherently weatherproof.
Which of the following is a source of loss in coaxial feed line?
AnswerWater intrusion, high SWR, and multiple connectors can all contribute to coaxial feed-line loss.
Coaxial feed-line loss can increase because of water intrusion, mismatch-related current and voltage effects from high SWR, and additional connector losses.
What can cause erratic changes in SWR?
AnswerLoose connection in the antenna or feed line
A loose or intermittent antenna or feed-line connection changes the impedance seen by the transmitter, causing SWR to jump around unpredictably.
What is the electrical difference between RG-58 and RG-213 coaxial cable?
AnswerRG-213 cable has less loss at a given frequency
RG-213 is physically larger and has lower attenuation than RG-58 at the same frequency, making it better for longer runs or higher-frequency use.
Which of the following types of feed line has the lowest loss?
AnswerAir-insulated hardline
Air-insulated hardline uses large conductors and very low-loss dielectric construction, giving it lower attenuation than ordinary flexible coaxial cable.
What is standing wave ratio (SWR)?
AnswerA measure of how well a load is matched to a transmission line
Standing wave ratio compares the voltage maxima and minima that result when a load does not perfectly match a transmission line. It is therefore a measure of impedance match quality.