CBT - Certified Broadcast Technologist RF and Antenna Systems Questions and Answers

Question 1

A broadcast station is experiencing periodic signal fade and unexpected long-distance reception of its VHF signal, particularly on hot, calm days.
This phenomenon is most likely caused by which of the following?

Accepted Answer

Tropospheric ducting

Answer

Ionospheric skip

Answer

Ground wave propagation

Answer

Multipath cancellation from a nearby structure

Question 2

What is the primary function of a radome on a broadcast antenna?

Accepted Answer

To protect the antenna from environmental elements

Answer

To amplify the transmitted signal

Answer

To change the antenna's polarization

Answer

To decrease the antenna's wind resistance by creating a vacuum

Question 3

An impedance mismatch between a transmitter's 50-ohm output and an antenna system results in a high Voltage Standing Wave Ratio (VSWR). Which of the following is a direct consequence of this condition?

Accepted Answer

A portion of the RF power is reflected back to the transmitter

Answer

Increased antenna gain

Answer

The frequency of the transmitted signal is shifted

Answer

Improved signal-to-noise ratio at the receiver

Question 4

A broadcast engineer is selecting an antenna for a new FM station. The antenna specification sheet lists its gain as 5 dBd. What is the equivalent gain expressed in dBi?

Accepted Answer

7.15 dBi

Answer

2.85 dBi

Answer

5.00 dBi

Answer

10.00 dBi

Question 5

For maximum signal transfer between a transmitting antenna and a receiving antenna in a line-of-sight system, which property of the antennas must be aligned?

Accepted Answer

Polarization

Answer

Bandwidth

Answer

Physical height

Answer

Voltage Standing Wave Ratio (VSWR)

Question 6

A technician at a television station notices that during periods of heavy icing, the transmitter's VSWR reading initially improves (decreases) before eventually worsening (increasing) as the ice accumulates further. What is the most likely reason for this initial improvement?

Accepted Answer

The antenna was originally tuned for a frequency slightly higher than the operating frequency, and the initial ice accumulation effectively 'lengthens' the elements, bringing them closer to resonance.

Answer

The ice acts as a lens, focusing the RF energy more efficiently.

Answer

The ice changes the antenna's polarization to circular, which is more robust.

Answer

The ice insulates the antenna, preventing power loss due to thermal radiation.