Linear and sinusoidal frequency changes of signals in a room

This paper investigates changes (modifications) of instantaneous frequency of signals with linear and sinusoidal frequency sweeps, as they propagate in a room. The modification of the instantaneous frequency of these signals is investigated numerically and experimentally. When interference with only a single reflected wave is considered, signals with a linear frequency sweep exhibit changes of instantaneous frequency proportional to the sweep rate, and to the delay time of the reflected wave. For sinusoidal modulation, changes in the instantaneous frequency depend mainly on the modulation frequency and the frequency deviation. Extreme excursions of the instantaneous frequency coincide in the time domain to minima of the amplitude envelope of the resultant signal. It is additionally shown from measurements in a real room, that increasing the modulation frequency causes a decrease in the frequency deviation of the signal in the room.