neliömodulaation

Neliömodulaatio, also known as square wave modulation, is a type of amplitude modulation where the modulating signal is a square wave. Instead of a smooth sinusoidal variation in amplitude, the carrier signal is switched abruptly between two distinct levels, typically representing the "on" and "off" states, or two different amplitudes. This switching is dictated by the modulating square wave.

The process involves multiplying the carrier signal by a square wave. If the square wave has an amplitude of +1 and -1, the carrier signal will be either unchanged or inverted. If the square wave is unipolar, for example with values of 0 and 1, the carrier signal will be either present or suppressed. The resulting modulated signal's spectrum will contain the carrier frequency and sidebands, but the nature of the sidebands will differ from that of sinusoidal amplitude modulation due to the harmonic content of the square wave.

Neliömodulaatio is simpler to implement electronically compared to traditional amplitude modulation, often requiring less complex circuitry. It finds applications in certain digital communication systems, control systems, and in some older forms of radio transmission where simplicity and robustness were prioritized. However, the presence of harmonics in the square wave can lead to a wider bandwidth requirement and potential interference issues.