Transmission media (A-level only) Flashcards – AQA A-level Physics (7408)

What is a ground wave?

A radio wave that travels near the Earth's surface.

How can a long-wavelength ground wave reach beyond the direct line of sight?

It diffracts around the Earth's curved surface.

Why is the useful range of a ground wave limited?

The signal weakens as it travels, including through interaction with the ground.

What is a sky wave?

A radio wave directed upwards that can return to Earth after interacting with the ionosphere.

What is the ionosphere?

A region of the upper atmosphere containing charged particles.

How can the ionosphere return a suitable radio wave to Earth?

Changes in its properties with height progressively refract the wave towards the surface. This return is often described as reflection.

Under what condition can a wave be reflected at a change in medium?

When the change in the medium is sufficiently abrupt.

What reception advantage can sky-wave propagation provide?

Reception beyond the direct line of sight.

What two factors determine whether a sky wave returns to Earth?

Its frequency and the state of the ionosphere.

What are the directions of the uplink and downlink in a satellite communication link?

The uplink carries a signal from Earth to the satellite; the downlink carries it from the satellite towards Earth.

What type of electromagnetic wave is commonly used for satellite links, and what is its typical frequency range?

Microwaves, typically at frequencies in the gigahertz range.

Why do satellite uplinks and downlinks use different frequencies?

Frequency separation allows the unwanted transmission to be filtered, reducing the risk that a strong transmitted signal will overwhelm a nearby receiver.

What is receiver desensitisation?

A reduction in a receiver’s ability to detect a weak wanted signal in the presence of a strong unwanted signal.