Ham Radio Technician Test Antennas & Feedlines 4 — Questions and Answers
Question 1: What is the effect of operating an antenna significantly off its resonant frequency without a tuner?
- High SWR and increased feedline loss (Correct answer)
- Lower noise floor on receive
- Increased antenna gain
- The transceiver automatically adjusts power
Correct answer: High SWR and increased feedline loss
Operating an antenna off-resonance causes a high SWR, which increases feedline losses and can stress the transmitter's output stage.
Question 2: For a vertical antenna mounted on a vehicle rooftop, the car body serves as:
- The ground plane (Correct answer)
- A director element
- A noise shield
- A loading coil
Correct answer: The ground plane
The metal vehicle body acts as the ground plane, providing the RF return path for the vertical antenna.
Question 3: What does antenna 'gain' mean in practical terms?
- Concentrating radiated power in a preferred direction compared to a reference antenna (Correct answer)
- Amplifying the signal inside the antenna element
- Increasing total radiated power beyond the transmitter output
- Reducing the feedline loss
Correct answer: Concentrating radiated power in a preferred direction compared to a reference antenna
Antenna gain is a measure of directivity — it focuses power in certain directions at the expense of others, not creating new power.
Question 4: Which connector type is commonly used with RG-8 or RG-213 coax for HF amateur radio?
- PL-259 (UHF connector) (Correct answer)
- SMA
- N-type
- F-type
Correct answer: PL-259 (UHF connector)
The PL-259 (sometimes called a UHF connector despite its name) is standard for HF amateur radio applications with large-diameter coax.
Question 5: What is a J-pole antenna?
- A half-wave radiator fed at the base via a quarter-wave matching stub (Correct answer)
- A dipole bent into a J shape to reduce wind loading
- A vertical antenna with a J-shaped ground radial
- A type of loop antenna for 40 meters
Correct answer: A half-wave radiator fed at the base via a quarter-wave matching stub
The J-pole uses a quarter-wave matching section (the 'J' foot) to feed a half-wave vertical element at its natural current maximum.
Question 6: What is 'coax velocity factor' and why does it matter?
- The speed of the signal in coax relative to free space; affects electrical length calculations (Correct answer)
- The rate at which coax heats under high power
- The frequency at which coax becomes lossy
- The ratio of coax impedance to antenna impedance
Correct answer: The speed of the signal in coax relative to free space; affects electrical length calculations
Velocity factor (typically 0.66–0.85 for common coax) means signals travel slower in coax than in air, shortening the electrical wavelength.
Question 7: What is the approximate free-space wavelength at 146 MHz?
- About 2 meters (6.6 feet) (Correct answer)
- About 10 meters (33 feet)
- About 70 centimeters (2.3 feet)
- About 20 meters (65 feet)
Correct answer: About 2 meters (6.6 feet)
At 146 MHz, the free-space wavelength is approximately 2 meters — which is why this band is called the '2-meter band.'
Ham Radio Technician Test Antennas & Feedlines 4
What is the effect of operating an antenna significantly off its resonant frequency without a tuner?