Ham Radio Technician Test Antennas & Feedlines 3 — Questions and Answers
Question 1: What is the impedance of a typical half-wave dipole antenna in free space?
- 73 ohms (Correct answer)
- 50 ohms
- 300 ohms
- 600 ohms
Correct answer: 73 ohms
A half-wave dipole in free space has a feed-point impedance of approximately 73 ohms.
Question 2: What happens to the SWR on a feedline if the antenna is perfectly matched to the line's characteristic impedance?
- SWR equals 1:1 (Correct answer)
- SWR equals 2:1
- SWR becomes infinite
- SWR depends on line length
Correct answer: SWR equals 1:1
A perfect impedance match results in an SWR of 1:1, meaning all power is transferred to the antenna with no reflections.
Question 3: What is the main disadvantage of using a very long coaxial feedline run at UHF frequencies?
- Significantly increased signal loss (Correct answer)
- Higher SWR due to cable length
- Increased radiation from the feedline
- Reduced antenna bandwidth
Correct answer: Significantly increased signal loss
Coaxial cable loss increases with frequency, so long runs at UHF can lose a substantial portion of your transmit power.
Question 4: Which type of antenna connector is most commonly used for handheld VHF/UHF transceivers?
- SMA (Correct answer)
- PL-259 (UHF)
- N-type
- BNC
Correct answer: SMA
SMA connectors are standard on most modern handheld (HT) transceivers due to their small size.
Question 5: What is the term for the ratio of the maximum to minimum voltage along a transmission line?
- Standing Wave Ratio (SWR)
- Voltage Standing Wave Ratio (VSWR) (Correct answer)
- Reflection coefficient
- Return loss
Correct answer: Voltage Standing Wave Ratio (VSWR)
Voltage Standing Wave Ratio (VSWR) specifically measures the ratio of maximum to minimum voltage amplitude along the feedline.
Question 6: A Yagi antenna's gain is primarily achieved by:
- Focusing radiation in one direction using directors and a reflector (Correct answer)
- Using a larger wire diameter
- Operating at multiple resonant frequencies
- Combining signals from multiple feedlines
Correct answer: Focusing radiation in one direction using directors and a reflector
A Yagi uses parasitic elements (directors in front, reflector behind) to concentrate radiation in the forward direction.
Question 7: What is an antenna tuner (also called an antenna coupler) used for?
- To match the transceiver's output impedance to the feedline and antenna system (Correct answer)
- To amplify the transmitted signal
- To filter out harmonics from the transmitter
- To measure field strength near the antenna
Correct answer: To match the transceiver's output impedance to the feedline and antenna system
An antenna tuner transforms the antenna system impedance to match the 50-ohm output of the transceiver, maximizing power transfer.
Ham Radio Technician Test Antennas & Feedlines 3
What is the impedance of a typical half-wave dipole antenna in free space?