Accurate AM Depth Measurement in the Presence of Angle Modulation

This paper will attempt at giving an insight into accurate amplitude modulation depth measurement on condition that the signal source is simultaneously amplitude and angle modulated by a harmonic signal. The first major part of this paper is on the theoretical power spectrum and the amplitude modulation depth analysis of such modulated signals, where we restrict ourselves to a weak angle modulation. Then a technique for proper AM depth calculation is discussed in respect of random properties of measured signal. Finally, the modified way of amplitude modulation depth measurement in the frequency domain is briefly introduced and a special attention is given to variety of amplitude modulation depth calculation methods. The reviews of results based on "classic " AM depth measurement and on proposed method and calculations are also presented and, in particular, some pitfalls to avoid during measurement and calculation are covered.