Commercial radio receivers

The paper describes three new radio receivers. They are designed to handle telegraphy, and continuous wave, as well as modulated continuous wave and telephony. The short-wave (13.5-250 m.) and medium-wave (250-500 m.) sets are built on the superheterodyne principle. The circuits are specially adapted to be equally efficient for telegraphy as for telephony reception. Thus, the automatic gain control has two alternative time-constants, the longer one being used when receiving high-speed telegraphy to avoid false operation by telegraph impulses, or noise. For reception of C.W. and searching for non-modulated carries the gain control valve is used as an oscillator (for audio-beat note). The receivers are equipped with click suppressors and, for telegraph reception, with band-pass filters, to increase the signal-noise ratio. The long-wave set (1500-22,000 m.) has a straight tuned circuit. When required a beat note can be obtained by bringing into use an auxiliary h.f. oscillator. Band-pass filters and noise suppressors are incorporated as in the other two sets. All three sets are provided with a wave switch which alters the selectivity characteristic of the receiver from flat (for tuning) to sharp (for reception). The sets can be battery or mains supplied. Sensitivity makes possible reception on a half-wave dipole with a field-strength of one microvolt per metre, atmospherics permitting.