Some recent developments in communication receiver design

Improvements in the achievement of frequency stability of local oscillators are described, particular reference being made to methods of compensating fot the effects of temperature and humidity changes, and of changes in valve characteristics. Receiver circuits employing crystal-controlled first oscillators are described. The advantages and disadvantages of electromechanical ifiters in increasing selectivity are considered, but it is concluded that these are not at present practicable because of their sensitivity to shock and the difficulties of production. Methods of improving frequency presentation are discussed, and optical and film scales are described which enable high resolution of frequency setting; band-switching arrangements are also described. Brief mention is made of the possible future use of transistors in communication receivers.