Telecommunications

Four students (A, B, C, D) completed a table regarding the orbit of a GPS satellite.

Which student is correct?

• A

• B

• C

• D

What feature of fibre optic cables has made them a suitable replacement for traditional copper-based cables?

• Lower bandwidth

• Higher attenuation

• Do not need repeaters over long distances

• Not susceptible to electromagnetic interference

Answer explanation

Attenuation: the reduction of the amplitude of a signal, electric current, or other oscillation

Which of the following is used to transmit data in a fibre optic cable?

• Air pressure

• Infrared light

• Plasma radiation

• Electrical voltage

Which statement best describes modulation?

• The addition of information to a carrier wave

• The attenuation of information in a carrier wave

• The removal of quantised information from a carrier wave

• The filtering of unnecessary information from a carrier wave

Which of the following electronic circuits functions as a NAND gate?

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A data signal wave has been modulated onto a carrier wave to produce a signal wave.

What type of modulation is shown?

• Demodulation

• Phase modulation

• Frequency modulation

• Amplitude modulation

A frequency shift key (FSK) is a frequency modulation scheme used to modulate a carrier with digital information. For the message signal shown, which sketch best shows the output of a frequency shift key (FSK) modulator.

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Television programs that show high levels of activity often have lower picture quality.

This is because television signals are transmitted using:

• Digital modulation at low compression levels

• Digital modulation at high compression levels

• Analogue modulation at low compression levels

• Analogue modulation at high compression levels

Which of the following can be safely transmitted by fibre optic cables?

• Microwaves

• Radio waves

• Gamma rays

• Infrared waves

Which of the following best describes the function of a zener diode in a telecommunication circuit?

• Voltage regulator

• Focused light beam

• Wide light beam

• Voltage director

Answer explanation

Zener diode - a voltage regulator which allows current to flow above a designated voltage. They provide a stable reference voltage across a wide range of current values.

Laser diodes emit a focused light beam when current flows through the circuit and are used to transmit pulses of light down an optical fibre to allow digital data transmission.

Light emitting diodes emit a WIDE beam of light when current flows through the circuit. They are commonly used to indicate if power is on

P-N Junction - n an electrical circuit allows current to flow more easily in one direction than another. Forward biasing means putting a voltage across a diode that allows current to flow easily, while reverse biasing means putting a voltage across a diode in the opposite direction.