Patent GB-541251-A (GB)
Title: Methods of automatically controlling the transmission characteristics in electric wave transmission systems
IPC: G01R13/20
Filed: 1940-06-01
Abstract: 541,251. Automatic control systems. STANDARD TELEPHONES & CABLES, Ltd. June 1, 1940, No. 9626. Convention date. June 3, 1939. [Class 38 (iv)] [Also in Groups XXXIX and XL] An automatic system for equalizing or balancing electric wave transmission systems on the basis of Heaviside's theory of indicial response comprises means for transmitting regularly repeated signals through a network, means for checking the response of the said network to succesive points of the signals, means for generating a current upon departure of said response from a predetermined norm, and means responsive to said current for adjusting the elements of the network to restore the response to the said norm. As shown in Fig. 9 the signal producing and controlling means comprises a terminated network DN provided with successive tappings t 1 , t 2  ... tn connected to a series of amplifiers A 1 , A 2 ...An. Impulses are fed to the network through terminals I 1 , I, and the outputs from the several amplifiers are combined to produce the signal sent out through terminals O, O 2 . The amplification of each amplifier is controlled separately by means of variable resistance F 1 , F, ... Fn in feed back circuits. The means for checking the signal may include a photo-electric conversion of the signal or may compare the signal directly against a master signal point by point by means of rotating commutator switches. In the photo-electric system, the signal is fed to a cathode-ray oscillograph adapted to reproduce on its screen the wave form on the screen, rows C 1 ...and C,<SP>1</SP> of square top wave, Fig. 5. On each side of this wave form on the screen, rows C,...and C,<SP>1</SP> of photo-electric cells are disposed, and each pair of opposed cells is connected to a pair of relays to control a respective amplifier A 1 ...of Fig. 9. If the wave form on the screen is correct, the cells are not affected ; but a deviation on one side or the other at any point of the wave form energizes one of the cells and this causes the automatic adjustment of the resistance of the corresponding amplifier, whereby the signal deviation is corrected. Modifications may be made in this photoelectric system, for example a single pair of cells may be used to check successive points of the wave form, the wave form or the cells being gradually displaced. A suitable relay device is shown in Fig. 2, each pair of relays 6, 6a having an armature 7 situated between them. The armature carries a rotatable resistance 4 fast with a gear wheel 5 between opposite pinions 13, 13d on shafts 2, 2a continuously driven by a motor 3. The wheel 5 is normally out of gear ; but energization of one relay or the other causes it to engage one of the pinions and to be thereby rotated in one direction or the other to adjust the effective resistance in circuit. The gearing shown may be replaced by clutch devices. A scale may be provided to indicate the position of the resistance. In the commutator system of checking the signal, the signal is fed to a checking device L, Fig. 7, connected to an emitter E of standard pulses and to a device G for generating short pulses according to the instantaneous values of the signal, which pulses are delayed by a device DN and fed back to the device L where they are compared with the standard pulses from the emitter E. Any deviation of the signal in one direction or the other causes one of the amplifiers AMP 1, AMP 2 connected to the checking device L to operate to apply corrections to the equalizer C. The devices L, G and amplifiers AMP 1, AMP 2 are connected respectively to the emitter E, the delay network DN and the equalizer C through synchronized commutators CMI, CM2, CM3, CM4. Specification 539,562, [Group XL], is referred to.