High density digital recording using videocassette recorders

A high density 12 Mbit/s digital recorder using a commercial videocassette recorder (VCR) has been developed for use in very long baseline interferometry (VLBI) systems. The recorder design emphasizes low cost, simplicity, and reliability. Partial response (1 - D²) signaling is used to obtain the most efficient use of the available bandwidth. In order to ensure consistent optimum performance of the system without requiring operator intervention, equalization, threshold detection, and gain control are all placed directly under microprocessor control. A clock recovery circuit using a digital phase lock loop designed to track the point of minimum intersymbol interference was developed. The performance of the system as a whole is discussed from the point of view of uncorrected bit error rates (BER´s) and the stability of the processor-directed control algorithms.