Ham Radio Technician Test Antennas & Feedlines 5

Question 1

What is the main advantage of a beam antenna (such as a Yagi) over a dipole for VHF weak-signal work?

Accepted Answer

Higher gain in a specific direction improves both transmit and receive performance

Answer

Beam antennas require no feedline matching

Answer

Beam antennas are omnidirectional and cover all directions simultaneously

Answer

Beam antennas eliminate multipath fading

Question 2

Which feedline type is immune to common-mode RF currents without additional chokes?

Accepted Answer

Open-wire ladder line

Answer

RG-8 coax

Answer

RG-58 coax

Answer

Twinlead (300 ohm)

Question 3

What is the purpose of antenna radials on a ground-mounted vertical?

Accepted Answer

They provide a low-loss RF ground return to complete the antenna circuit

Answer

They increase the antenna's resonant frequency

Answer

They act as parasitic directors for additional gain

Answer

They physically support the vertical element

Question 4

If you double the number of radials on a ground-mounted vertical from 8 to 16, what is the expected result?

Accepted Answer

Reduced ground losses and improved antenna efficiency

Answer

Doubled antenna gain in all directions

Answer

Increased SWR requiring re-tuning

Answer

No practical difference below 30 MHz

Question 5

What does 'dBd' mean when specifying antenna gain?

Accepted Answer

Gain relative to a half-wave dipole reference antenna

Answer

Gain relative to an isotropic radiator

Answer

Gain measured in decibels of power

Answer

Gain measured over a ground plane

Question 6

What is a common cause of RF feedback (RF in the shack) in a station with a coax-fed dipole?

Accepted Answer

Common-mode current flowing on the outside of the coax shield back into the shack

Answer

Excessive antenna height above ground

Answer

Using RG-213 instead of RG-58

Answer

Operating the antenna on a harmonic frequency

Question 7

What is the typical characteristic impedance of open-wire (ladder line) feedline?

Accepted Answer

300 to 600 ohms

Answer

50 ohms

Answer

75 ohms

Answer

93 ohms