In this paper it is shown that non-linear equalization by decision feedback offers such a large advantage in signal-to-noise ratio and bandwidth economy that a hybrid binary 140 Mbit/s system is possible with compatibility in repeater spacing in existing European ternary regenerative systems. A large number (60) of analog sections can be connected in tandem. Hardware models of analog and digital sections are described and a detailed analysiS of tolerances is given.

A method for designing conventional filters for decision feedback systems is described. Practical considerations, such as error propagation effect, timing inaccuracy and complexity, are incorporated in the design rules. In particular, non-band-limited noisy transmission channels and channels impaired by bandwidth limitation are investigated. In addition, noise and bandwidth limitations are taken into account simultaneously. The design approach is based upon polynomial descriptions which reveal simple relationships between the forward and feedback path, a stability measure which is representative of the error propagation, and an evaluation in terms of Laguerre polynomials. Results of simulations in hardware are given by way of a practical example and a binary regenerative transmission system for coaxial cables is studied.

The bandwidth penalty of digital systems is very obvious in the case of transmission over coaxial cables because of the exponential increse of cable attenuation with square root of frequency. From capacity point of view, it is only at very high information rates (> 500 Mbit/s typically) that a digital system might be competitive with an analog system, because the disadvantage of noise accumulation in an analog system ultimately cancels the bandwidth penalty of the digital system. In addition, it is, however, difficult to realize common functions, such as amplification, equalization, regeneration, clock extraction, etc. with electronic components having a frequency range comparable to the frequency range of the information signal, which extends from zero frequency to the microwave range. Besides, the complexity of a regenerative repeater should be kept to a minimum for reliability reasons. It is shown in the paper that with present-day technology a 560 Mbit/s repeater can be constructed, operating in sections of 1.5 km coaxial cable (2.6/9.5 mm). Also, we demonstrate that new technologies exist which may lead to repeaters with a high degree of monolithic integration, even at such a speed, which is important from the reliability viewpoint. The constructed and described repeater is characterized by unconventional and economic design of amplifier/equalizer and clock extractor and by monolithically integrated decision circuits.

An analysis is presented of the performance of phaselocked timing extraction circuits for baseband pulse code transmission. The phase error of the extracted timing wave is influenced by the properties of three essential stages in signal processing: prefiltering, nonlinear treatment, and narrow-band filtering. The analysis enables us to calculate quantitatively the quasi-static and the dynamic part of the phase error for arbitrary but specified types of signal processing. This is more than can be done with existing theory in the case of resonant-type timing extraction circuits. Examples are given for practical cases, and conditions for optimum performance are derived. Furthermore, the behavior of such phase-locked circuits in a chain of repeaters is investigated, and in particular, the propagation law for jitter. Byrne's model, as used for resonant-type timing extraction circuits, therefore is generalized. It is shown analytically and experimentally that by proper implementation of the timing extraction circuit, considerable improvement can be obtained as compared with resonant-type circuits.