CBT RF Transmission & Antenna Systems 3

Question 1

What is beam tilt in a broadcast antenna, and why is it used?

Accepted Answer

Directing the main lobe of the antenna pattern slightly below horizontal to improve ground-level coverage

Answer

Tilting the antenna mast to improve structural stability

Answer

Rotating the antenna beam azimuthally to cover a wider service area

Answer

Increasing the vertical beamwidth to improve high-angle coverage for aircraft

Question 2

What is the purpose of null fill in a broadcast antenna system?

Accepted Answer

To reduce the sharp signal nulls in the vertical radiation pattern that cause coverage gaps

Answer

To eliminate all sidelobes from the vertical radiation pattern

Answer

To increase the antenna's forward gain in the horizontal plane

Answer

To prevent energy from radiating upward past 90 degrees elevation

Question 3

When two FM stations on the same frequency are co-located, what minimum carrier-to-interference ratio is generally required to protect the desired signal?

Accepted Answer

30 dB

Answer

6 dB

Answer

20 dB

Answer

50 dB

Question 4

What is a transmission line's velocity factor (VF), and how does it affect electrical length calculations?

Accepted Answer

VF is the ratio of signal speed in the line to the speed of light; electrical length = physical length divided by VF

Answer

VF is the ratio of signal amplitude to noise; higher VF means lower noise

Answer

VF is the line's impedance divided by free-space impedance; used to calculate reflection loss

Answer

VF is the percentage of RF power lost per meter of line at the operating frequency

Question 5

What is the function of a hybrid combiner in a broadcast RF system?

Accepted Answer

To combine two transmitter outputs onto one antenna while isolating the transmitters from each other

Answer

To convert a balanced transmission line to an unbalanced coaxial system

Answer

To split one transmitter's output equally to feed two separate antennas

Answer

To filter spurious emissions below the FCC mask requirement

Question 6

What is the significance of the FCC's 60 dBu and 54 dBu contours for Class C FM stations?

Accepted Answer

They define the protected service contour and the interference contour respectively

Answer

They define the maximum power levels allowed at the transmitter output

Answer

They specify the minimum antenna gain required for full-power operation

Answer

They represent the upper and lower limits of the FM stereo pilot subcarrier

Question 7

Which measurement technique is used to determine the antenna VSWR of an in-service broadcast antenna without taking the transmitter offline?

Accepted Answer

A directional wattmeter measuring forward and reflected power in the transmission line

Answer

Time Domain Reflectometry (TDR) with a live carrier

Answer

A spectrum analyzer sweep of the antenna input port

Answer

A Q-meter measurement at the antenna feed point