Transistor feedback amplifiers in carrier telephony systems

Because equipment using transistors will be introduced into communication networks in which valve equipment is already in use, questions of compatibility will arise. In some cases the performance of transistor equipment will have to conform closely to that of existing valve equipment, whilst, in others, no such restriction will occur. With present transistors this latter case would lead to the use of low signal levels and low-gain amplifiers. With feedback amplifiers employed in carrier systems the effect is to divide the amplifiers into two classes. The first class must operate with high gains and high output powers, whilst the second class is essentially one of low-power amplifiers. Examples of both classes are described, and various features of their design are discussed. These are a high-power amplifier suitable for use on an open-wire line system, a low-power wide-band amplifier for use on a system for pair cables, and a narrow-band feedback amplifier of the type used in pilot control systems. Future developments are briefly discussed.