What does the communications section cover in WJEC A-Level Electronics?

It covers how information is sent over a communication system: the transmitter, channel and receiver, the need for a high-frequency carrier, amplitude and frequency modulation, bandwidth and data rate, and noise and distortion. It also covers transmission methods: radio-wave transmission and the aerial, attenuation of a signal with distance, optical-fibre transmission by total internal reflection, and the difference between multimode and monomode fibre.

Why is a carrier needed in a communication system?

A carrier is a high-frequency signal onto which the information is modulated. It is needed because a low-frequency information signal such as audio cannot be radiated efficiently from a practical aerial; an efficient aerial must be comparable in length to the signal's wavelength, and audio wavelengths are kilometres long. Modulating the audio onto a high-frequency carrier allows transmission from a reasonable aerial, and different carriers let many stations share the channel.

What is the difference between AM and FM?

In amplitude modulation (AM) the amplitude of the carrier is varied in step with the information while its frequency stays constant. In frequency modulation (FM) the frequency of the carrier is varied while its amplitude stays constant. FM is more resistant to noise because the information is in the frequency, not the amplitude, so amplitude noise can be clipped before demodulation; the trade-off is that FM needs a wider bandwidth than AM.

How does an optical fibre carry light, and why is monomode used for long distance?

An optical fibre guides light along a glass core of higher refractive index than the surrounding cladding. Light striking the core-cladding boundary above the critical angle undergoes total internal reflection and stays in the core. Multimode fibre has a wide core allowing many light paths, which spreads pulses (modal dispersion) and limits the data rate over distance. Monomode fibre has a very narrow core with essentially one path, almost eliminating dispersion, so it gives a much higher data rate over long distances.

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WJEC A-Level Electronics Communications Systems: modulation, bandwidth, radio and optical fibre explained

A deep-dive WJEC A-Level Electronics guide to Communications Systems. Covers the structure of a communication system, the need for a carrier, amplitude and frequency modulation, bandwidth and data rate, noise and distortion, radio-wave transmission and the aerial, attenuation, optical-fibre transmission by total internal reflection, and multimode versus monomode fibre.

Generated by Claude Opus 4.813 min readWJECUpdated 2026-06-16

Reviewed by: AI editorial process; not yet individually human-reviewed

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What the communications section demands
Communication principles and modulation
Wireless and optical transmission
How the communications section is examined
The topics, dot point by dot point
For the official specification

What the communications section demands

Communication is how electronics moves information from place to place, and the WJEC specification covers both the principles (modulation, bandwidth, noise) and the physical methods (radio and optical fibre). The topic rewards clear explanations and a few standard calculations on sidebands and bandwidth.

This guide walks through the two topics in specification order, then sets out the exam patterns WJEC repeats. Each topic has a matching dot-point page with worked exam questions; this overview ties them together.

Communication principles and modulation

A communication system has a transmitter (which modulates the information onto a high-frequency carrier), a channel, and a receiver (which demodulates it). A carrier is needed because low-frequency information cannot be radiated efficiently from a practical aerial. In amplitude modulation (AM) the carrier's amplitude is varied; in frequency modulation (FM) its frequency is varied. AM produces sidebands at the carrier plus and minus the modulating frequency, giving a bandwidth of twice the highest modulating frequency. Data rate rises with bandwidth, and noise and distortion degrade the signal. FM resists amplitude noise better but needs more bandwidth.

Wireless and optical transmission

Radio transmission radiates a modulated carrier from an aerial sized to the wavelength; the signal weakens through attenuation and gains noise with distance. Optical-fibre transmission guides light along a glass core of higher refractive index than the cladding by total internal reflection above the critical angle. Multimode fibre has a wide core (many paths, modal dispersion, lower data rate over distance); monomode fibre has a narrow core (one path, much higher data rate over long distances). Fibre offers higher bandwidth, lower attenuation and immunity to interference compared with copper.

How the communications section is examined

Expect AM sideband and bandwidth calculations, the AM-versus-FM noise comparison, the carrier justification, the total-internal-reflection explanation of optical fibre, and the multimode-versus-monomode comparison. These are reliable marks built on a few clear ideas.

The topics, dot point by dot point

Each topic has a dot-point answer page with worked exam questions and cross-links. Browse them from this overview and the subject hub.

For the official specification

WJEC Eduqas publishes the full specification, past papers and mark schemes at eduqas.co.uk. Always revise from the current specification and the board's own past papers, because question style is board-specific.

Sources & how we know this

WJEC Eduqas GCE A-level Electronics specification — WJEC Eduqas (2017)