About modulation and carrier

The baseband signal is the original electrical signal, which generally refers to the basic signal waveform. In digital communication modulation technology, it refers to the corresponding electrical pulse. In Wireless telemetry and remote control systems and radio technology, modulation is to use baseband signals to control parameters (amplitude, frequency, and phase) of high-frequency carriers so that these parameters change with the baseband signals. The baseband signal used to control high-frequency carrier parameters is called a modulated signal. Unmodulated high-frequency electrical oscillation is called a carrier (it can be a sine wave or a non-sine wave, such as a square wave or a pulse sequence ).

Dual modulation is often used in radio communication. The first step is to use a digital signal or analog signal to modulated the first carrier (referred to as the sub-carrier ). Or use modulation technology in Multi-Channel Communication to achieve multiplexing (frequent division multiplexing and time division multiplexing ). In step 2, a public carrier (referred to as a carrier) is modulated with the tuned sub-carrier or multiplexing signal for radio transmission. The second step of modulation is called secondary modulation. High-frequency carriers are modulated by baseband signals, which can reduce the antenna size during radio transmission and facilitate long-distance transmission. The Application of modulation technology can also improve the signal anti-interference capability.