Page 7 - Topic 3

Horizontally polarised

RADIO AND TELEVISION SIGNALS
Information that we receive on our devices, such as radios and televisions, is sent through the air using antennae.
The antennae transmit and receive radio or television waves.

They are usually made up of aluminium rods and convert electric current into electromagnetic radiation
(transmitters) and vice versa (receivers).

They are designed to receive these signals within a certain frequency range and as such their physical size usually
correlates to the amplitude of the wave.

The polarisation of the waves are also important. If the receiver is not in the same polarisation as the transmitter,
then the receiver cannot pick up the wave.

TRANSMITTING A SIGNAL
To transmit a signal, an alternating potential difference (often referred to as the radio frequency RF) is applied to the
transmitter. This causes the electrons in the metal to oscillate along the aluminium which causes an electric wave to
be produced. This then induces the creation of electromagnetic radiation like we mentioned previously.

RECEIVING A SIGNAL
When the electromagnetic radiation reaches the receiving antennae, if they are plane polarised, the wave causes the
electrons in the material to move with the same frequency as the transmitting signal. This then causes the receiving
system to have an alternating potential difference (RF). This is then interpreted by the receiving device as a picture
or sound.

QUESTIONS
Workbook. Questions 88-89 page 314 onwards.