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L.C. Thomas, Bell Telephone Labs., Inc.
This paper is basically concerned with determining readback distortion in magnetic recording. This determination is obtained, not by closed-form analysis, but by simulation of the readback system, consisting of the head and load. The simulation environment allows the author to avoid two limiting assumptions of the past. In this case, he is able to treat a head of finite permeability and a nonzero load. The load considered is a rather standard and adequate parallel RC network. For the finite permeability head, an RL series equivalent circuit is used in which the resistance and inductance are frequency dependent and determined experimentally. The argument is made that the open-circuit readback voltage (zero load) is linear with the input (variation of flux in the storage medium). This fact allows superposition to be applied, and the actual readback voltage computed at the various harmonics of the input. Since R and L vary with frequency, a different equivalent circuit of the head applies for each harmonic. The analysis and superposition of the linear network responses for each network is performed digitally. Finally, some digital filtering is performed in an attempt to offset the effects of distortion, to no avail.
L.C. Thomas, "R68-9 A Computer Simulation of Electrical Loss and Loading Effect in Magnetic Recording," IEEE Transactions on Computers, vol. 17, no. 3, pp. 298-300, March 1968, doi:10.1109/TC.1968.229107
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