Modulation is the process of converting an information signal into a radio wave by varying one or more of its characteristics, such as amplitude, frequency, or phase.

AM radio broadcasting uses amplitude modulation, where the amplitude of the carrier wave is varied in accordance with the information signal.

FM is less susceptible to noise than AM because the information is encoded in the frequency of the carrier wave, which is less affected by noise than the amplitude.

Digital radio broadcasting uses quadrature amplitude modulation (QAM), which is a digital modulation technique that uses two carrier waves with different phases to transmit data.

A radio transmitter is used to transmit the radio wave through the air, typically using an antenna.

A radio receiver is used to convert a radio wave into an information signal, typically using an antenna and a demodulator.

The range of frequencies used for radio communications spans from 3 kHz to 30 GHz, covering various applications such as AM and FM broadcasting, mobile communications, satellite communications, and radar.

Using higher frequencies for radio communications allows for increased bandwidth, which enables the transmission of more data or higher-quality signals.

Using higher frequencies for radio communications results in reduced range due to increased attenuation and diffraction, making it less suitable for long-distance communication.

A radio antenna is used to transmit and receive radio waves, acting as an interface between the radio transmitter or receiver and the surrounding space.

Isotropic antennas have a uniform radiation pattern, meaning they transmit and receive signals equally in all directions, while directional antennas have a focused radiation pattern, concentrating signals in a specific direction.

A radio repeater is used to extend the range of the radio signal by receiving the signal, amplifying it, and retransmitting it, allowing for communication over longer distances.

Simplex communication uses a single frequency for both transmission and reception, while duplex communication uses two frequencies, one for transmission and one for reception, allowing for simultaneous communication.

A radio spectrum analyzer is a device used to measure the power, frequency, and modulation type of a radio signal, providing valuable information for analyzing and troubleshooting radio communication systems.