sagedusdevatsioon

Sagedusdevatsioon, or frequency deviation, is the difference between the instantaneous frequency of a modulated carrier and its nominal or center frequency. It describes how far the carrier frequency moves from its center value in response to the modulation signal. Deviation can be positive or negative, depending on the direction of the frequency shift, and is typically measured in hertz.

In frequency-modulated (FM) communications, the deviation Δf is a central parameter. It represents the peak difference between the instantaneous carrier frequency and the unmodulated carrier. The allowable deviation is specified by standards and applications; for example, many regions use a maximum of ±75 kHz for FM broadcast, which, along with the highest modulating frequency, determines the channel bandwidth via rules such as Carson’s rule, B ≈ 2(Δf + fm). The modulation index is β = Δf / fm, where fm is the highest modulating frequency.

Measurement and units: Deviation is measured with specialized equipment such as deviation meters or spectrum analyzers and is expressed in hertz. In oscillator design and timing hardware, frequency deviation also describes short-term drift or long-term stability, often expressed in parts per million (ppm) or parts per billion (ppb).

Relevance: Accurate control of frequency deviation is essential for reliable demodulation, avoiding adjacent-channel interference, and meeting regulatory limits. Excessive deviation can cause distortion and spectrum widening, while insufficient deviation can degrade signal quality and intelligibility.