The purpose of a radio signal is to carry information. In radio communications, two basic elements make the propagation of a radio wave (which carries the signal) happen: a transmitter and a receiver. It is these elements that provide the signal the method to go from one place to another.
Signals are modulated into radio groups so they can be transmitted. The information that needs to be carried (sound for example) is converted in electrical signals and applied to the carrier wave which is produced by the transmitter.
There are two main kind of modulations as all those who own a radio know: AM and FM.
AM stands for Amplitude modulation and refers to a kind of modulation in which it’s the amplitude of the radio signal that is varied in order to carry the needed information – the frequency remains continued. FM stands for Frequency Modulation, and as it’s easy to imagine, acts on the frequency of the radio signal while the amplitude stays unvaried.
For a radio broadcast, the amplitude (AM) and the frequency (FM) radio groups are what carry information
FM groups are “line of sight” groups and consequently they travel in a straight line that can be interrupted by a multitude of obstacles. The FM groups are not refracted by the ionosphere (the upper part of Earth’s air that takes its name from the ion particles that occupy it) and consequently they can propagate past the Earth air and go into space.
AM is the older kind of modulation used – the groups can travel above the ground following the Earth curvature and because they are refracted by the ionosphere they can propagate farther than FM ones which ultimately leave Earth for the space.
An AM signal is unfortunately more inclined to interferences because of its smaller bandwidth and consequently has worst sound quality than the higher-bandwidth FM signal. It is also more prone to noise which affects amplitude, not frequency. However modulation and demodulation of AM signal is less complicate than in FM systems, and consequently AM is nevertheless widely used.
Once the information is applied on the carrier wave, an antenna transforms the electrical signal to an electromagnetic wave which is then propagated. The electromagnetic wave is then inclined to alterations due to reflection (which can happen due to obstacles), refraction (due to hitting the ionosphere or because of weather conditions) or diffraction (when radio groups hit and bend around an object with sharp ends) before it reaches the receiver aerial.
It is thanks to the receiver that this signal is intercepted, picked up, demodulated (re-converted), and the communicated information can be processed, shared, relayed or broadcasted to an audience.
Once the receiving antenna has detected the radio signal, it’s the receiver that filters out unwanted signals and retains only the desired frequencies – it also increases the strength of a signal with an amplifier and finally demodulates the signal.
In summary, radio signals, by the use of a transmitter such as a tower at the radio stop, are converted into electromagnetic groups, to be sent by the air to a receiver which detects the transmitted signal and decodes the information (anything like a an audio signal, a video signal or a digital signal) to a usable form using a demodulator. After being once again transformed back into an electronic signal it typically reaches a device like a speaker and the intended audience.
During radio transmission, it is important to know there may be some loss of the signal as it can be affected by distortion and/or degradation by undesirable physical noise – these are events that can arise and be unplanned and tend to affect the clarity of the intended message.
With radio communication, for the most part, the quality and clarity of reception is largely dependent on the following factors:
- kind of modulation
- Broadcasting strength of radio groups
- Time of day
- Geographic location of transmitting/receiving signals