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The authors analyse the performance of a mixed analogue-digital modulation technique called signal code modulation (SCM). The technique is based on the idea of representing the analogue signal by a digital (i.e. quantised) component, and an analogue component consisting of the quantisation error. The combination of these digital and analogue components provides an exact representation of the original signal. Both components are transmitted by the communication system and used to reconstruct an estimate of the signal at the receiver. The presence of the analogue residual allows system performance to improve when excess channel SNR is available. The digital component provides an SNR gain and makes it possible to employ coding to achieve near-error-free transmission. The performance of the SCM method is analysed in some detail.