Recording and Reproduction of NRZI Signals

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Abstract
A systematic theoretical study of a saturation type of recording and reproduction in digital magnetic tape systems was undertaken so that the details of these processes could be more clearly understood. The dependence of tape magnetization and of output signal pulse width and amplitude on the major system parameters has been investigated and determined. These parameters are the magnetic field distribution of the recording head, write current waveform, tape thickness and hysteresis characteristics, head-to-tape spacing, reading gap length, and bit density. A portion of this study is presented here, concerning the extension of the sinusoidal theory to include the reproduction of signals resulting from saturation recording. This is done by a Fourier analysis of the tape magnetization and a term-by-term summation of harmonic responses to obtain the resultant signal. The results show why high writing field gradients, high tape B-H “squareness,” and thin tapes are needed for high-density recording. They indicate possible reasons for emf pulse peak position asymmetries during readback. Two examples of output calculations are included. One shows the signal amplitude and pulse width vs bit density, compared with experimental measurements. The other presents the field distribution above the magnetized tape, indicating the influence of the presence of the read head.

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