Quadrature amplitude modulation (QAM) was found to suitable for the bandpass type frequency characteristic of magnetic recording/reproducing channels. A method of 20 Mbps signal recording using 32 QAM coded modulation is described.

Recording and reproducing of quadrature amplitude-modulated (QAM) signals on magnetic recording channel of VCR is studied. While the frequency characteristics of QAM signal is nearly matched to that of the magnetic recording channel, the linearization of magnetic transmission channel associated with odd-order nonlinear transfer function is considered to be essential to record QAM signals, and the employment of bias recording method is experimented for this purpose. Simple 16 QAM and coded 32 QAM signals are recorded on an experimental VCR. It is found that the SNR required by coded 32 QAM signal is lower than that by 16 QAM signal for the channel SNR higher than 14 dB. Coded 32 QAM signals of 20 Mbps data rate are recorded and reproduced at a scanning speed of 3.5 m/s using a head of 50 µm track width, and the word error rate less than 10-5 is successfully accomplished.

To study lower sideband enhancement, three kinds of modulation methods are applied to recording. Compared with results of experiments using a VCR and simulations, it is concluded that the order of magnitude of lower sideband enhancement is AM, Dual-frequency, FM with lower modulation index.