Sending Analog Waves

Imagine I wanted to send a signal which consisted of a 200Hz pure note.

I would need this signal to be "carried" by a radio wave with a much higher frequency. There are two ways of doing this.

Amplitude Modulation (A.M.)

Frequency Modulation (F.M.)

An electrical oscillation in a transmitter produces electromagnetic radio waves. These travel through the air. If they pass through an aerial they produce electrical oscillations in it which are converted into a varying p.d. A tuning circuit is set to resonate at the frequency of the carrier wave so these oscillations are amplified and the signal is filtered out from it.

The electromagnetic spectrum is big but each radio station is assigned a very small part of it or else they would all interfere with each other.

In the case of f.m. transmission they will need a chunk starting at the carrier wave frequency and ending at this frequency + the amount of modulation required i.e. the highest frequency in the actual signal. The difference is called the required bandwidth (although we shall see later that this phrase can have several meanings).

Bandwidth = Difference between highest and lowest frequencies in a signal