A Radio is a device used for communication. It works by receiving the transmission of signals, either by modulation or electromagnetic waves, on frequencies below the visible light spectrum. Radio waves travel by oscillating electromagnetic fields that pass through air and space while carrying information that systematically changes its properties like amplitude, frequency, or phase. When the radio waves pass through an electrical conductor, the oscillating fields cause an alternating electrical current and its detection is what produces sounds. The waves are sent and picked up through antennas, which adjust in size based on the frequency range they are tuned to hear.
The very first radio every functional was produced on August 14, 1894 and was incapable of transmitting sound or speech. It was called the “wireless telegraph” and is more formally known as Morse code. Then on May 7, 1895 the first radio receiver was successfully tested and contained a coherer. In 1896 the first patent was awarded for a radio receiver with electrical impulse signals and in 1897 the first radio broadcast was aired. It wasn’t until the early 1900s that developments were made allowing the AM radio stations to be used for aeronautical navigation. Radio Navigation was the primary means of air travel up until the 1960s when the Very High Frequency Omni-Directional Beacon Radio (VOR) was developed and quickly took the place of AM radio navigation. Today VORs are still in use and are quickly being replaced by Satellite Radio, more commonly known as GPS or ADS-B.
Today radio is used for pretty much all kinds of communication. We still have FM and AM radio broadcast stations, which are what you hear every time you turn on your car radio. More recently, we have developed digital radio which is used in broadcasting videos, phone calls, TVs, and of course Blue Tooth.
More specifically to aviation, radios are used for communications and navigation. In order to receive instructions from air-traffic control, the pilot needs to dial a certain frequency into the radio. This allows the pilot to send and receive transmissions to both people on the ground and planes in the air. Radios are also used by ground-based transmitters and satellite transmitters to aid the pilot in navigation. Things like VORs and DMEs (distance measuring equipment) use timing differences between radio signals sent to transmitters and received from the transmitters to determine position and location to the transmitter. With satellite radio, primarily GPS, signals are sent to a receiver on the airplane from four different satellites. One for longitude and latitude, one for altitude, one for time, and one to verify that the timing is correct. Since the satellite is so far away from the receiver time becomes a factor when determining location. If it takes the signal two seconds to reach the satellite the receiver two seconds to respond to the satellite then the receiver is actually is four seconds ahead of where it started by the time it gets a signal back from the satellite. This is why the fourth satellite is needed to correct the timing. GPS navigation is becoming more popular today but the basic technology used to develop it still originated from early 1900s radio.