In an era of ever more promising electronic developments, digital techniques are offering exciting challenges to the designers of communications equipment. With digital systems, great stores of information can be transmitted speedily and accurately. The human voice can be converted for communication not only with humans but with machines. With more refinements in digital techniques, machines will communicate with one another.
Most engineers agree that the advantages of digital communications techniques in-clude: the ability to eliminate noise and distortion at each repeater; greater accuracy than analog systems; and the ability to use error-detection and correction codes.
Disadvantages are: complex equipment; limited transmission speed; the need for increased bandwidth; the need to quantize analog signals; and the possibility of quantizing noise.
Solid-state devices permit the design of smaller, more efficient equipment and open the way to operation at higher frequencies with less costly equipment.
Many digital systems are in use today. Pulse duration modulation (PDM) or pulse-width modulation (PWM) are commonly used; pulse amplitude modulation (PAM), delta modulation and pulse code modulation (PCM) also are being developed. Most experts feel that PCM offers the greatest possibilities for future exploitation. (Electronic Design, June 8, 1960, p. 52)
These are the lead paragraphs to a report on digital communications, published at a time when there was still a debate over the best modulation techniques. The photo shows a demonstration PCM-tv repeater link from Bell Labs.