The design of band-spread tuned circuits for broadcast receivers

The paper deals with the various factors in broadcast receiver design which are of particular importance when band-spread tuning is employed, stress being laid throughout on the practical aspects. The first two Sections deal briefly with the way in which this method was developed to meet the need for easier tuning on short-wave bands, and with the various methods employed to achieve it. The general design of the pre-selector and oscillator circuits is then discussed in some detail. The basic circuit for band-spread tuning by variable capacitance is analysed, and formulae are developed for calculating the elements of the capacitance network. From these, graphical methods of solution are developed and illustrated. The use of temperature-compensating condensers, and various methods of circuit trimming, are also discussed. In conclusion, it is shown that there scope for considerable divergence in design to suit the various price ranges of receivers, and that, although the best methods, as usual, cost more, the simpler methods can, by careful design, be made reasonably good. There is, however, the risk that poor design and excessive cheapening might cause the system to fall into disrepute.