fluktfreqens

Fluktfreqens is a concept used in Dutch-language signal processing and metrology to describe the time-dependent fluctuations of a signal’s frequency around a nominal carrier. In practice it refers to the instantaneous frequency deviations δf(t) = f_i(t) − f0, where f_i(t) is the instantaneous frequency derived from the signal phase. The term covers short-term jitter, drift, and noise-induced variations in frequency, arising from source oscillators, transmission media, or modulation schemes.

Mathematically, if a carrier is expressed as s(t) = A(t) cos(2π f0 t + φ(t)), the instantaneous frequency is f_i(t) = f0 + (1/2π) dφ(t)/dt, and fluktfreqens describes the stochastic process δf(t). It is commonly analyzed via the power spectral density S_f(f) of δf(t) or via the fractional frequency fluctuations y(t) = δf(t)/f0, with its own spectral density S_y(f).

Measurement and analysis draw on phase-noise and frequency-stability methods: analytic signals, Hilbert transform, frequency counters, and demodulation; or metrological tools such as Allan deviation and related metrics.

Causes include oscillator phase noise, environmental perturbations (temperature, supply voltage), and modulation schemes, as well as Doppler or multipath effects in communication links. Fluktfreqens is closely related to, and overlaps with, phase noise and frequency noise concepts; it is used to assess oscillator quality, link performance, and timing precision.

See also: Phase noise, Frequency stability, Allan variance, Instantaneous frequency, Jitter, Modulation.