Communications are changing. Mobile phone signals, radio and television have, or will soon be switching over from analogue to digital technology.
Analogue signals vary continuously. They are very prone to interference, because it is hard to separate the original signal from spurious signals.
Digital signals consist of a stream of zeros and ones - basically off and on. The signal to be transmitted is changed into a stream of zeros and ones by sampling the signal many times per second. The signal sent does not include only the information that is transmitted, but also extra information (also in the form of zeros and ones) which enables any error in the signal (which shows up as a zero being sent being received as a one) that means this error can be easily detected and corrected. This means no loss in the quality of the signal between being transmitted and received, because although errors may creep in very easily - because as the signal travels along, it gets weaker, so noise becomes relatively more important – digital signals are much easier to process and the errors are easier to detect than with analogue signals.
Radio, television and mobile phone calls all used to be transmitted as analogue signals. This restricted the amount of information that could be transmitted, made them prone to interference, and also meant in the case of mobile phones, that signals were difficult to make secure and easy to eavesdrop. Digital signals are easy to encrypt, so can be made very secure. At the receiving end, the sigmals can be unencrypted as required, and decoded – turned back into analogue signals.