Measurement of Transfer Characteristics Using FM Signals in a Magnetic Image Recording System

Abstract

A new measurement scheme for transfer characteristics using FM signals is proposed for the magnetic recording system of a VCR. The modulating signal of the FM signal is sinusoidal. The transfer characteristics are calculated from the complex frequency spectra of the FM signals before recording and after playback. A few cycles of an unmodulated FM carrier signal are added before the modulated FM signal as a phase reference signal. Several methods are introduced to reduce the influences of the phase reference point, jitter, and skew, and the transfer characteristics of an S-VHS VCR are measured. The experimental results show that the phase characteristic is approximately linear, and varies very little with the recording level. The amplitude characteristic is very nearly an odd function of the frequency centered at the carrier frequency, and it varies with the recording level, especially in the uppersideband.