By Harry J. Reichert, Jr,. General Instrument Jerrold Division
The usefulness of a viable return signal path associated with an existing forward system signal distribution system is of greater value now than ever before. With this objective in mind it seems worthwhile to review some of the established methods which have been designed to make this objective a technical reality as well as to offer a recently developed technique which will prove to be a valuable addition to any two way system maintenance program.
This new technique was developed to combat COMMON PATH DISTORTION which is a relatively recent addition to the list of distortions which occur in bidirectional cable systems. When the conditions exist in a system that cause this distortion, interference is generated by the forward system signals which impacts the return system frequency spectrum. This potentially interfering energy is often misidentified as ingress when the return system is viewed on a spectrum analyzer. The mechanism which causes this distortion and a method to isolate this system problem will be described in detail.