A History of Radio Communication
The first modern forms of long-distance communication were telegraph and later telephone>; these used vast networks of wires to send information
Towards the end of the 19th century, much research was being done in to the sending and receiving of signals without wires. This was developed by the likes of Marconi, who were equipping ships with this technology to improve safety. This technology was further developed so that information such as sound (radio) and pictures (television) could be broadcast and received.
Radio Waves and Communication
Remember that radio waves are part of the electromagnetic spectrum.
They are sent from transmitters and can travel in one of 3 ways, depending on their wavelength
A barrier in the transmission of radio waves is diffraction, this is the apparent bending of waves around obstacles.
This diffraction is influenced by the wavelength of the radio waves: a radio wave with a large wavelength is able to diffract around obstacles, whereas the smaller wavelengths will not. Look at the example below of the houses in the hills.
It is not able to receive short wavelength broadcasts, but can pick up the long.
Amplitude Modulation (AM) and Frequency Modulation (FM)
Remember that the amplitude of a wave is its displacement from the normal and frequency is how often the wave occurs. See properties of waves.
AM and FM are two ways that signals are represented in radio waves and you will recognise these terms being used on your radio set. Here is a quick comparison of the two:
Noise affects the amplitude of a wave more readily so signal can be lower quality.
Have a longer distance range.
Higher quality reception since noise doesn't affect frequency.
Has a shorter range.