Patent GB-197296-A (GB)
Title: Improvements in or relating to electric signalling systems
IPC: H03H9/48
Filed: 1923-02-27
Abstract: 197,296. McCaa, D. G. May 2. 1922, [Convention date]. Tone frequency tuning-arrangements; thermionic heterodyne receivers.-Low-frequency currents of definite frequency, particularly those arising from heterodyne or other wireless receiving- systems, are selectively transmitted to a telephone or other indicator through tuned vibratory members such as stretched bands, tuning forks, &c., which are set in vibration by the received currents, and themselves set up vibratory currents in a secondary circuit, the vibrations being damped by the resistance of the tuned circuits. The vibratory members may be in two sections loosely coupled. A cascade of such arrangements may be employed, and auxiliary means may be provided for mechanically damping the vibrations. Fig. 2 shows one arrangement of the apparatus for wireless reception. Beat currents in the transformer secondary s are passed through coils d around the poles of a magnet h. The magnet has a centrally-pivoted armature controlled by a spring m and connected by a link o to a stretched band or string F, which is thus set in vibration. A second band G preferably forming a continuation of the band F is connected by a link o to the armature of a magnet h, the vibration of the armature inducing currents in the coils d which pass through a transformer x and if desired through amplifiers H to the telephone T. Further pairs of bands such as F, G may be employed, and means such as the condensers C<3>, C' may be provided for electrical tuning. The degree of coupling between the bands F, G may be reduced, thereby giving finer tuning, by broadening the support w dividing the bands, or by providing a plurality of spaced supports between the input section F and the output section G. The bands F, G, in addition to being damped by the resistance of the tuned circuits, may be damped by forming the bands of magnetic material passing through the air gap of an electromagnet. The separate or coupled band sections F, G may be replaced by a single section connected to the input and output armatures j. The output band G, instead cf vibrating an armature, may be arranged to vary the resistance or impedance of a circuit including a source of current, thereby causing variations of current strength in that circuit. The stretched bands may be replaced by tuning forks or reeds. As shown in Fig. 9, the input armature j vibrates a diaphragm K at one end of a telescopic tube I, J forming a tuned air column. A diaphragm L at the other end is connected to the armature j of the current-inducing magnet. The beat currents in the coil s, Fig. 2, are caused by the combined action of the incoming signals, (which are applied in phase agreement to the grids g of a double detector valve V<1>) and of currents from the local oscillator V<2> which are applied to the same grids in phase opposition. In another system described the incoming signals are first heterodyned so as to produce supersonic beat currents which are then combined with currents from the local source V<2> to produce audible beats. The audio-frequency currents may be produced by simple rectification when receiving spark or tonic train signals, or by a ticker or tone wheel if receiving continuous wave signals. The Specification as open to inspection under Sect. 91 (3) (a), refers to the use of damping pads adjustably pressed on the bands F. G. This subject-matter does not appear in the Specification as accepted.