Patent GB-242013-A (GB)
Title: Improvements relating to electrical signalling systems, particularly to wireless receiving systems
IPC: H04B1/08
Filed: 1924-08-16
Abstract: 242,013. Hale, G. W., and Lyle, R. Aug. 16, 1924. Addition to 223,630. Inductive signalling; receiving systems and apparatus; thermionic amplifiers and detectors; relaying and repeating systems.-Relates to the system described in the parent Specification for distributing telephonic or telegraphic signals received by wireless or cable signalling, in which the signals, after amplification by a multi-stage valve amplifier, are used to create an electrostatic field which influences disconnected telephones; and comprises the following modifications :- (1) The disconnected telephone receiver, Fig. 1, is provided with a condenser 46, which may be housed within one ear-piece 37, or upon the head-band 48, connected in shunt to the series-connected coils 39, 40, 42, 43. The condenser tends to by-pass the higher voice frequencies, thus counteracting the distortion inherent in this system of signal distribution. The ends of the series-connected coils are connected respectively to a metal headband, surrounded by insulation, and to one of the ear-pieces 37, the cap 36 of which makes conductive or capacitative connection with the head of the wearer. The local field set up by the signals creates a difference of potential between the listener's body and the metal head-band, causing signal current to pass through the coils. A shunt resistance may supplement or replace the shunt condenser. A modified form of receiver shown in Fig. 2 comprises a single ear-piece 49 mounted on a handle 50. The electrostatic pickup device comprises the listener's body on the one hand, and on the other hand a fan 51 formed of metal or of metal wires 52 covered with silk &c. The fan may be collapsed within a recess in insulating section 50 of the handle. The ends of the telephone coils are connected respectively to the fan and to the metal end-piece 55 of the handle, or to the ear-piece, 49, either of which makes conductive connection with the listener's body. A condenser 46 mounted on the handle is connected across the telephone coils. (2) When the received signals are of high-frequency and are not rectified before passing to the amplifier and to the distributing network, a crystal detector is mounted in one of the ear-pieces, or on the head-band, and is connected between the earpiece casing and the phone windings. (3) The tendency of the distribution system to emphasize. the higher voice frequencies is neutralized by modifying the amplifier so as to produce distortion in the opposite sense. The coupling between the detector valve and the following amplifying valve may include, a choke coil, shunted by a condenser, which tends to by-pass the higher frequency components, and to reduce their effect on the subsequent valves of the amplifier. (4) When the distributing network is at some distance from the amplifier, transformers may be arranged so that the connecting cable is at low voltage. A step-down transformer is connected in the plate circuit of the last valve, the secondary being connected to the conducting cable. The distributing network is connected through a voltageadjusting switch to the secondary coil of a stepup transformer, the primary of which is connected 'to the conducting cable. One end cf each coil is earthed'. In a modification shown in Fig. 7, a choke coil 27<a> is connected in the plate circuit of the last valve 19, and one wire of the cable 78 is connected through a large condenser 81 to a point on the choke, the other wire of the cable 78 being earthed. The network 30 is connected through a switch 29 to the secondary coil of the step-up transformer 27. The valve 19 should be a low-impedance valve of large capacity, or a group of such valves connected in parallel. The cable 78 may be armoured, and the armouring may form the earth return.