Lesson 9. Antennas and Feedlines

Question 1

Which of the following types of antenna offers the greatest gain?

A. 5/8 wave vertical

B. Isotropic

C. J pole

D. Yagi

Answer 1

D. Yagi

Note:
The Yagi antenna is a directional antenna and offers the greatest gain. If you are unable to increase your radio’s power output, antenna gain can offer you an advantage of more power through antenna performance and design!

Question 2

What is an advantage of a 5/8 wavelength whip antenna for VHF or UHF mobile service?

A. It has more gain than a 1/4-wavelength antenna

B. It radiates at a very high angle

C. It eliminates distortion caused by reflected signals

D. It has 10 times the power gain of a 1/4 wavelength whip

Answer 2

A. It has more gain than a 1/4-wavelength antenna

Question 3

What is a benefit of low SWR?

A. Reduced television interference

B. Reduced signal loss

C. Less antenna wear

D. All of these choices are correct

Answer 3

B. Reduced signal loss

Question 4

What is the major function of an antenna tuner (antenna coupler)?

A. It matches the antenna system impedance to the transceiver’s output impedance

B. It helps a receiver automatically tune in weak stations

C. It allows an antenna to be used on both transmit and receive

D. It automatically selects the proper antenna for the frequency band being used

Answer 4

A. It matches the antenna system impedance to the transceiver’s output impedance

Question 5

What is a disadvantage of the short, flexible antenna supplied with most handheld radio transceivers, compared to a full-sized quarter-wave antenna?

A. It has low efficiency

B. It transmits only circularly polarized signals

C. It is mechanically fragile

D. All of these choices are correct

Answer 5

A. It has low efficiency

Note:
Rubber duck antennas offer more convenience than performance. There is nothing wrong with owning two separate antennas for your handheld radio. The rubber duck can be used for close-quarter or tactical communications where most everyone or the repeater is line of sight. A quarter-wave antenna can be substituted for conditions where performance is a priority such as hiking or locations farther away from other individuals or the repeater.

Question 6

Why is coaxial cable the most common feed line for amateur radio antenna systems?

A. It is easy to use and requires few special installation considerations

B. It has less loss than any other type of feed line

C. It can handle more power than any other type of feed line

D. It is less expensive than any other type of feed line

Answer 6

A. It is easy to use and requires few special installation considerations

Question 7

Which of the following types of feed line has the lowest loss at VHF and UHF?

A. 50-ohm flexible coax

B. Multi-conductor unbalanced cable

C. Air-insulated hard line

D. 75-ohm flexible coax

Answer 7

C. Air-insulated hard line

Question 8

What happens as the frequency of a signal in coaxial cable is increased?

A. The characteristic impedance decreases

B. The loss decreases

C. The characteristic impedance increases

D. The loss increases

Answer 8

D. The loss increases

Note:
This is why coaxial cable used in VHF and UHF installations cost more than coaxial cable used on HF frequencies. Longer runs of coaxial cable for VHF and UHF installations should be avoided, if possible. Your antenna system is one of the most important pieces of your station.

Question 9

What is antenna gain?

A. The additional power that is added to the transmitter power

B. The additional power that is required in the antenna when transmitting on a higher frequency

C. The increase in signal strength in a specified direction compared to a reference antenna

D. The increase in impedance on receive or transmit compared to a reference antenna

Answer 9

C. The increase in signal strength in a specified direction compared to a reference antenna

Question 10

Which of the following RF connector types is most suitable for frequencies above 400 MHz?

A. UHF (PL-259/SO-239)

B. Type N

C. RS-213

D. DB-25

Answer 10

B. Type N

Note:
They have less loss than other types of coaxial cable connectors. Also, N connectors have much better shielding than other connectors rated for HF use. The extra shielding keeps stray RF from leaking out of the connector and also helps prevent strong RF fields from leaking into the system. Type N connectors are available in both solder and crimp styles.

Question 11

What is the most common impedance of coaxial cables used in amateur radio?

A. 8 ohms

B. 50 ohms

C. 600 ohms

D. 12 ohms

Answer 11

B. 50 ohms

Note:
Nearly all amateur radio transmitters are designed to use coaxial feed lines with a 50-ohm impedance. The coaxial cable used for television, CATV, cable and satellite installations is all 75 ohm. At first glance, the cable looks the same, but a close examination of the cable type printed on the jacket will allow you to reference the specifications on a data sheet.

Question 12

Which of the following RF connector types is most suitable for frequencies above 400 MHz?

A. UHF (PL-259/SO-239)

B. Type N

C. RS-213

D. DB-25

Answer 12

B. Type N

Note:
Type N connectors are most suitable for frequencies above 400 MHz. They have less loss than other types of coaxial cable connectors. Also, N connectors have much better shielding than other connectors rated for HF use. The extra shielding keeps stray RF from leaking out of the connector and also helps prevent strong RF fields from leaking into the system. Type N connectors are available in both solder and crimp styles.

Question 13

Which of the following increases the resonant frequency of a dipole antenna?

A. Lengthen it

B. Insert coils in series with radiating wires

C. Shorten it

D. Add capacitive loading to the ends of the radiating wires

Answer 13

C. Shorten it

Note:
Shortening a dipole antenna will make it resonant on a higher frequency. Just think of the musical instrument with strings: the shorter the string, the higher the frequency; the longer the strings, the lower in frequency. If your antenna presents a high SWR on the frequency you wish to operate, then look at the SWR above your frequency and below your frequency. If the SWR is better below your current frequency you know you will have to shorten your antenna to raise its resonant frequency.

Question 14

In which direction does a half-wave dipole antenna radiate the strongest signal?

A. Equally in all directions

B. Off the ends of the antenna

C. Broadside to the antenna

D. In the direction of the feed line

Answer 14

C. Broadside to the antenna

Question 15

Which of the following describes a type of antenna loading?

A. Electrically lengthening by inserting inductors in radiating elements

B. Inserting a resistor in the radiating portion of the antenna to make it resonant

C. Installing a spring in the base of a mobile vertical antenna to make it more flexible

D. Strengthening the radiating elements of a beam antenna to better resist wind damage

Answer 15

A. Electrically lengthening by inserting inductors in radiating elements

Question 16

What is a disadvantage of using a handheld VHF transceiver with a flexible antenna inside a vehicle?

A. Signal strength is reduced due to the shielding effect of the vehicle

B. The bandwidth of the antenna will decrease, increasing SWR

C. The SWR might decrease, decreasing the signal strength

D. All of these choices are correct

Answer 16

A. Signal strength is reduced due to the shielding effect of the vehicle

Note:
A disadvantage of using a handheld VHF transceiver with its integral antenna inside a vehicle while mobile is that signals might not propagate well because of the vehicle’s shielding effect. If practical, an external magnetic mount antenna will deliver superior performance. Also be aware that some cities and states have laws about operating handheld electronic devices while driving. Some vehicles have material in the window tinting that also has a shielding effect on VHF and UHF frequencies. Think safety.