The Solid-State Receiver in the TL Radio System

When the junction transistor was first announced, it was apparent to many that it would eventually replace the electron tube as an active element in many communications systems. Its small size, low power drain, ruggedness, reliability, and potentially low cost all contribute to its widespread usefulness in the development of new electronic circuits and in the redesign of existing apparatus. The growth in diversity of applications is directly related to the properties of the devices which become available or can be made available in production quantities. This article reports on another step in this expansion -- solid-state circuits for a wideband microwave communications system. The development of this new system became both technically feasible and economically practical when diffused-base transistors with excellent high-frequency performance and reliability became available in large quantities at low cost. 1831 18.36 THE BELL SYSTEM TECHNICAL J O U R N A L , NOVEMBER 1962 Although improvements in device capabilities were very important, the success of the development described herein is due also to the application of new circuit design concepts which differ considerably from conventional electron tube circuit design practice. These innovations and their supporting philosophy will be discussed. The TL radio relay system as a whole will be described in another article. 1 That article should be consulted for an over-all system description and for the results of early field applications.