Radio Components – How Radio Devices Work

Aviation radios are transceivers. They both transmit and receive radio waves. (They send and receive communication)

• Sound Waves are converted to an electric message via a Microphone
• There are different types of microphones, that vary in how they convert sound and the quality that they achieve.

A radio transmitter consists of several elements that work together to generate radio waves.

• Microphone (Transducer): Converts voice (pressure in the form of sound waves) to an electrical information (voltage).
• Oscillator: It creates an alternating current at the frequency on which the transmitter will transmit. The oscillator usually generates a sine wave, which is referred to as a carrier wave.
• Modulator: It adds useful information to the carrier wave. There are two main ways to add this information. The first, called amplitude modulation or AM, make slight increases or decreases to the amplitude of the carrier wave. The second, called frequency modulation or FM, make slight increases or decreases the frequency of the carrier wave.
• Amplifier: It amplifies the modulated carrier wave to increase its power. The more powerful the amplifier, the more powerful the broadcast.
• Antenna: It converts the amplified signal to radio waves.

A radio receiver is the opposite of a radio transmitter. It uses an antenna to capture radio waves, processes those waves to extract only those waves that are vibrating at the desired frequency, extracts the audio signals that were added to those waves, amplifies the signals.

• Antenna: It captures the radio waves. Typically, the antenna is simply a length of wire. When this wire is exposed to radio waves, the waves induce a very small alternating current in the antenna.
• RF amplifier: A sensitive amplifier that amplifies the very weak radio frequency (RF) signal from the antenna so that the signal can be processed by the tuner.
• Oscillator: It creates an alternating current at the frequency on which corresponds with the tuned frequency. This carrier wave will be used as a base for the removal process by the detector.
• IF Amplifiers: A two stage amplifying process.
• Detector: It is responsible for separating the audio information from the carrier wave.
• Audio amplifier: This component’s task is to amplify the weak signal that comes from the detector so that it can be heard. A squelch circuit controls the Audio amplifier, to remove undesired noise.

Different antennas for different functions (eg HF, VHF, VOR, GPS, ELT). The length of the antenna must be ½ the wavelength, often they can use the aircraft itself to supply ¼ of this wavelength.

VHF antennas (1/4 wavelength) are low drag stub units placed on the top (and bottom) of the aircraft fuselage (body). Larger aircraft have more VHF radios (usually 3) and will have at least one antenna on the bottom of the fuselage.

If shielded by buildings or other parts of the aircraft, the reception will be reduced or not received.

For most aircraft, antennas are used for both transmitting and receiving.