Some types of low noise amplifier

The need for amplifiers with optimum noise performance is discussed, with particular reference to the requirements of space communication. The paper then deals with the application of vacuum tubes, transistors, masers, parametric amplifiers and tunnel diodes to the problem of obtaining a low-noise receiver in the frequency range 100¿1000 Mc/s. The advantages and disadvantages of these devices are discussed. Experimental results, with a brief outline of the underlying theory, are given for a varactor amplifier used as a preamplifier to a u.h.f. receiver. Results are also given for a transistor used as a self-oscillating mixer showing conversion gain and a low noise figure. Consideration is then given to the application of these devices to the various frequency ranges and means of optimizing parametric amplifier noise figures.