Wireless and Radio Defined
Communicating wirelessly does not require radio. Everyone's noticed how appliances like power saws cause havoc to A.M. radio reception. By turning a saw on and off you can communicate wirelessly over short distances using Morse code, with the radio as a receiver. But causing electrical interference does not constitute a radio transmission. Inductive and conductive schemes, which we will look at shortly, also communicate wirelessly but are limited in range, often difficult to implement, and do not fufill the need to reliably and predictably communicate over long distances. So let's see what radio is and then go over what it is not.
Weik defines radio as:
"1. A method of communicating over a distance by modulating electromagnetic waves by means of an intelligence bearing-signal and radiating these modulated waves by means of transmitter and a receiver. 2. A device or pertaining to a device, that transmits or receives electromagnetic waves in the frequency bands that are between 10kHz and 3000 GHz."
Interestingly, the United States Federal Communications Commission does not define radio but the U.S. General Services Administration defined the term simply:
1. Telecommunication by modulation and radiation of electromagnetic waves. 2. A transmitter, receiver, or transceiver used for communication via electromagnetic waves. 3. A general term applied to the use of radio waves.
Radio thus requires a modulated signal within the radio spectrum, using a transmitter and a receiver. Modulation is a two part process, a current called the carrier, and a signal which bears information. We generate a continuous, high frequency carrier wave, and then we modulate or vary that current with the signal we wish to send. Notice how a voice signal varies the carrier wave below:
This technique to modulate the carrier is called amplitude modulation. Amplitude means strength. A.M. means a carrier wave is modulated in proportion to the strength of a signal. The carrier rises and falls instantaneously with each high and low of the conversation.The voice current, in other words, produces an immediate and equivalent change in the carrier.