Ham Radio General Class Test Ham Radio General Class Test Antennas and Feed Lines Questions and Answers 2 — Questions and Answers
Question 1: What is the primary advantage of using open-wire (ladder line) feed line instead of coaxial cable?
- Much lower loss at high SWR (Correct answer)
- Higher power handling at UHF frequencies
- Better shielding from interference
- Easier to route through walls
Correct answer: Much lower loss at high SWR
Open-wire feed line has significantly lower loss than coax when operated at high SWR, making it ideal for multi-band antenna systems.
Question 2: What is the approximate length of a half-wave dipole antenna for 14.2 MHz?
- 33 feet (Correct answer)
- 50 feet
- 22 feet
- 66 feet
Correct answer: 33 feet
A half-wave dipole length is calculated as 468 divided by frequency in MHz, so 468/14.2 equals approximately 33 feet.
Question 3: Which type of antenna provides horizontal polarization when mounted parallel to the earth's surface?
- A dipole (Correct answer)
- A quarter-wave vertical
- A ground-plane antenna
- A J-pole
Correct answer: A dipole
A dipole antenna mounted horizontally radiates a horizontally polarized signal.
Question 4: What does a balun do when used at the feed point of a dipole antenna?
- Converts between balanced and unbalanced systems (Correct answer)
- Increases the antenna gain by 3 dB
- Filters harmonics from the transmitted signal
- Matches any impedance to 50 ohms
Correct answer: Converts between balanced and unbalanced systems
A balun converts between the balanced feed point of a dipole and the unbalanced coaxial feed line, reducing common-mode currents.
Question 5: What is the feed point impedance of a quarter-wave ground-plane antenna with the radials bent downward at 45 degrees?
- About 50 ohms (Correct answer)
- About 75 ohms
- About 25 ohms
- About 300 ohms
Correct answer: About 50 ohms
Bending the radials of a ground-plane antenna downward to 45 degrees raises the feed point impedance to approximately 50 ohms, providing a good match to common coaxial cable.
Question 6: What is the effect of feed line loss on SWR readings taken at the transmitter?
- SWR appears lower than the actual value at the antenna (Correct answer)
- SWR appears higher than the actual value at the antenna
- Feed line loss has no effect on SWR readings
- SWR readings become unstable and fluctuate
Correct answer: SWR appears lower than the actual value at the antenna
Feed line loss attenuates both the forward and reflected power, causing the SWR measured at the transmitter to appear lower than the true SWR at the antenna.
Ham Radio General Class Test Ham Radio General Class Test Antennas and Feed Lines Questions and Answers 2
What is the primary advantage of using open-wire (ladder line) feed line instead of coaxial cable?