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

A beam antenna's directional gain increases effective radiated power on transmit and reduces noise from unwanted directions on receive.

Question 2

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

Accepted Answer

Open-wire ladder line

Answer

Open-wire ladder line is balanced and symmetrical, so it does not support common-mode currents the way coax can.

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

Buried or on-surface radials create a low-resistance ground system that minimizes losses in the soil and completes the antenna circuit.

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

Doubling radials reduces ground resistance and ground losses, increasing the power actually radiated by the antenna.

Question 5

What does 'dBd' mean when specifying antenna gain?

Accepted Answer

Gain relative to a half-wave dipole reference antenna

Answer

dBd means decibels of gain compared to a half-wave dipole; dBi compares to an isotropic radiator (dBd = dBi − 2.15).

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