Patent GB-520609-A (GB)
Title: Improvements in or relating to directional radio receivers
IPC: H04N11/00
Filed: 1938-11-15
Abstract: 520,609. Directive wireless systems. CARPMAEL, A. (Telefunken Ges. Fur Drahtlose Telegraphie). Nov.15, 1938, No. 33232. [Class 40 (v)] In a homing receiver designed to give both visual and audible indications, the aerial pick-up is periodically reversed and the visual indicator is fed through a second synchronous switch, whilst the headphones are fed through another switch, which is operated in the rhythm of complementary signals. As shown in Fig. 8 the frame and open aerials AR, AH are alternately combined to give a reversed cardioid by the switch Ul and the combined signal is fed to the visual indicator JN through the rectifiers S1, S2 and a. synchronouslyoperated switch U2. Part of the combined signal is also fed to the headphones T through the switch U3 operating in dot-dash rhythm, the dots passing through valve R÷1 and the dashes through valve R÷2. These valves are rendered alternately conductive in synchronism with the switch U2 by means of biasing voltages taken from across the visual indicator so that for any one position of this switch, e.g. contact U2r, only one valve e.g. R÷1, is conductive and only one type of complementary signal, e.g. dot, is heard. When the receiver is " off course " dots and dashes of unequal intensity are heard, but for " on course" positions they are of equal intensity and produce a continuous note of a pitch corresponding to the frequency of operation of the switch U2. The switches shown may be driven from a common shaft, oralternativelv valve switching circuits may be used. In a modification, Fig. 9, the two valves are replaced by a single valve 4 to the grid of which a constant audio frequency f is applied. The voltages obtaining across the equi-signal switch controlled visual indicator 1 are also applied to the grid of valve 4, which is biased to the mid-point of its characteristic, through the switch 5 operating in dot-dash rhythm, the amplification of the valve being then varied with the switching. For " on course" positions signals of equal intensity are heard. Distortion of the note heard caused by the input to valve 4 including a frequency due to the aerial switching may be eliminated by fitting a filter between the indicator 1 and potentiometer 2. In order to eliminate the flicker of the visual indicator, a further transformer 13, Fig. 11, is interposed between the rectifier 11 and equi-signal switch 12 of the indicator 8 to prevent the D.C. component of the signal from affecting the instrument. The transformer 13 produces an A.C. voltage, Fig. 13a, from the rectified signal, Fig. 12 a, alternate half cycles of which are reversed by the switch 12 giving a fluctuating D.C. voltage, Fig. 14 a, the polarity of which depends upon the sense of the deviation from the course. Figs. 2 and 3 (not shown) illustrate a known form of visual indicating homing receiver operated by equi-signal switching and Figs. 5-7 (not shown) illustrate a known form of homing receiver giving visual and aural indications in which the aerials are switched in dot-dash rhythm the receiver output being applied in parallel to an audio indicator and to a rectifier, the output from which is passed through a transformer to give pairs of'adjacent impulses of opposite polarity which operate a ballistic visual indicator.