CBT - Certified Broadcast Technologist Broadcast Transmission Systems Questions and Answers

Question 1

In a broadcast transmission system, what is the primary function of an isolator?

Accepted Answer

To protect the transmitter's power amplifier from reflected power.

Answer

An RF isolator is a two-port passive device that allows RF signals to pass in one direction with very low loss, while absorbing and dissipating any power flowing in the reverse direction. This protects the transmitter's final power amplifier from damage or performance degradation caused by high levels of reflected power from the antenna or transmission line.

Question 2

A television station needs to transmit both its main VHF channel and a new UHF channel from the same antenna. Which device is required to combine these two signals onto a single transmission line without interference?

Accepted Answer

A diplexer

Answer

A diplexer is a three-port device that combines or separates signals based on their frequency. It uses filters (typically a low-pass and a high-pass) to allow signals from two different frequency bands, such as VHF and UHF, to share a common transmission line or antenna.

Question 3

Which modulation method is the standard for over-the-air terrestrial broadcasting in the ATSC 1.0 digital television system?

Accepted Answer

8-VSB (8-level Vestigial Sideband)

Answer

The ATSC 1.0 standard, used for digital television broadcasting in North America, specifies 8-VSB as the modulation scheme for terrestrial broadcasts. This method uses a single carrier and modulates it to one of eight amplitude levels to encode the digital data.

Question 4

A transmitter has an output power of 1,000 watts. The transmission line has a loss of 3 dB, and the antenna has a gain of 10 dBi. What is the Effective Isotropic Radiated Power (EIRP)?

Accepted Answer

5,000 watts

Answer

To calculate EIRP, first convert the transmitter power to dBW: 10 * log10(1000W / 1W) = 30 dBW. Then, apply the formula: EIRP (dBW) = Transmitter Power (dBW) - Transmission Line Loss (dB) + Antenna Gain (dBi). So, EIRP = 30 dBW - 3 dB + 10 dBi = 37 dBW. Finally, convert 37 dBW back to watts: 10^(37/10) = 5011.87 watts, which is approximately 5,000 watts.

Question 5

Which of the following would result in a Voltage Standing Wave Ratio (VSWR) of 1:1 on a transmission line?

Accepted Answer

The load impedance perfectly matches the characteristic impedance of the line.

Answer

A VSWR of 1:1 represents a perfect impedance match, where the load impedance is equal to the characteristic impedance of the transmission line. In this ideal case, all power is transferred to the load, and there is no reflected power. An open or short circuit would result in an infinite VSWR.

(CBT) Certified Broadcast Technologist Practice Test

(CBT) Certified Broadcast Technologist Practice Test

CBT - Certified Broadcast Technologist Broadcast Transmission Systems Questions and Answers