Applications of Electromagnetic Waves: Digital and Analogue Communication

Many modern communications send information using electromagnetic (EM) waves. Different parts of the spectrum are chosen for different jobs because they travel and carry data in useful ways.

Analogue vs Digital signals

• Analogue: a smooth, continuous signal that can take any value. A microphone makes an analogue electrical copy of your voice.
• Digital: a signal that has only two levels, usually written as $0$ and $1$. Sound can be sampled and stored as a series of bits.

Benefits of digital: high data rates, easy error checking, and long range because receivers can regenerate the clean $0/1$ shape even when noise has added small distortions.

Which EM waves are used?

• Radio waves: broadcast radio and TV, walkie‑talkies, RFID. Bluetooth uses very low‑energy radio/microwaves that can pass through walls but the signal becomes weaker.
• Microwaves: mobile phones, Wi‑Fi, and satellites. Microwaves pass through clouds and some walls and work with small aerials. Satellites mostly use microwaves:
  • Geostationary satellites (used for direct broadcast TV and some satellite phones) stay above one point on Earth.
  • Low‑orbit satellites (used by some satellite phones) give shorter delay because they are closer.
• Infrared/Visible in optical fibres: cable TV and high‑speed broadband. Glass is transparent to these wavelengths, so light is guided along fibres with low loss and can carry very high data rates.

How information is carried

• Analogue modulation: change the carrier’s amplitude (AM) or frequency (FM) to match the sound wave.
• Digital signalling: send pulses for $0$ and $1$. Even if noise blurs a pulse, the receiver decides which level it was and restores it. Repeaters boost and reshape the signal, increasing range.

Common misconceptions

• Digital is not a different kind of wave; it is a different way of encoding information on an EM wave.
• Microwaves used for communication are low power and very different from microwave ovens in energy delivered to the body.
• Walls can weaken signals; they do not block all radio or microwaves.