Experimental determination of the loss and phase transfer functions of a magnetic recording channel

The loss transfer function of a magnetic recording channel can be readily measured, but delay between writing and reading prevents simple measurement of the phase function. A method is described for experimental determination of these functions for a binary digital magnetic recording channel under conditions similar to normal use, so that the effects of channel parameter variations can be determined. The method involves writing a binary data sequence, reading the resulting output, digitizing and calculating the desired functions by use of the Fast Fourier Transform. A measurement system for achieving adequate accuracy in scanning, sampling and synchronization is described. Examples illustrate the results obtainable, and compare AC biased with unbiased recording, and with theoretical model calculations.