Angle modulation indices measurement in the presence of amplitude modulation

This paper presents an automated measurement of the phase/frequency indices of angle modulation in the frequency domain on condition that a signal source is simultaneously angle and amplitude modulated by the same phase shifted harmonic signals. In the first part of this paper, we propose mathematical model of such modulated signals. Then we investigate the spectrum of signal and discuss some basic properties of such modulated signals, where we restrict ourselves only to a weak amplitude modulation with modulation depth smaller than 100 %. The final section is devoted to the signal parameters derivation techniques based on the power spectrum measurement and non-linear least squares iteration method. The effect of power spectrum measurement errors is also pointed out and a comparison between Bessel null method and proposed technique is presented.