Technician exam: antennas and feed lines
Antenna types and length, polarization, SWR, coaxial cable and connectors. 23 questions, 10 at a time, starting with ones you haven't seen.
Rules to remember10 key antennas and feed lines rulesShow the rules
- A beam antenna, such as a Yagi, focuses most of its signal in one direction, giving gain that way and less elsewhere. (p. 67)
- Polarization is named for the direction of the electric field, so a vertical antenna produces vertical polarization. (p. 68)
- A short flexible rubber antenna is much smaller than a quarter wave, so it radiates less efficiently and gives a weaker signal. (p. 68)
- A 5/8-wave whip sends more energy toward the horizon, giving more gain than a quarter-wave antenna. (p. 69)
- A half-wave dipole radiates most strongly broadside, at right angles to the wire, and least off its ends. (p. 69)
- None of these common connectors is fully waterproof, so all of them should be sealed and taped when used outdoors. (p. 69)
- Most amateur coax is 50 ohms, matching the output impedance of typical transceivers. (p. 69)
- Coax loss rises as frequency goes up, which is why UHF stations favor better, lower-loss cable. (p. 70)
- An SWR reading that jumps around usually means an intermittent connection somewhere in the antenna or feed line. (p. 71)
- RG-213 is thicker than RG-58 and has lower loss at the same frequency, as well as handling more power. (p. 71)
Taken from the explanations to checked practice questions; page numbers link to the official handbook.
Sample antennas and feed lines questions
1.Which of the following connectors should be carefully taped for weather protection when used outdoors?
- AType N
- BBNC
- CPL259
- DAll these choices are correct
Show the answer
✓ D. All these choices are correct
None of these common connectors is fully waterproof, so all of them should be sealed and taped when used outdoors.
2.What is a potential drawback of using a handheld VHF transceiver inside a vehicle that lacks an externally mounted antenna?
- AThe handheld will overheat due to reflected power in the vehicle
- BThe SWR might decrease, decreasing the signal strength
- CThe bandwidth of the antenna will decrease, increasing SWR
- DSignal strength is reduced due to the shielding effect of the vehicle
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✓ D. Signal strength is reduced due to the shielding effect of the vehicle
A vehicle's metal body blocks much of the signal from a handheld used inside it, so an outside antenna works far better.
3.Why is a 19-inch-long vertical antenna often used on 2 meters?
- AIt has high gain
- BIt is a resonant half-wave
- CIt is a resonant quarter-wave
- DIt has low RF radiation exposure
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✓ C. It is a resonant quarter-wave
A quarter wavelength at 146 MHz is about 20 inches in free space and about 19 inches in practice after end-effect shortening, so a 19-inch vertical is resonant on 2 meters.
4.What is the major function of an antenna tuner (antenna coupler)?
- AIt matches the antenna system impedance to the transceiver's output impedance
- BIt automatically selects the proper antenna for the frequency band being used
- CIt allows an antenna to be used on both transmit and receive
- DIt helps a receiver automatically tune in weak stations
Show the answer
✓ A. It matches the antenna system impedance to the transceiver's output impedance
An antenna tuner transforms the antenna system's impedance to what the transmitter expects, usually 50 ohms.