Patent GB-197077-A (GB)
Title: Improvements relating to apparatus for the reception of signals in wireless and other forms of tuned telegraphy and telephony
IPC: H04B1/12
Filed: 1922-02-20
Abstract: 197,077. Bolitho, J. B. Feb. 20, 1922. Atmospherics and undesired signals, eliminating or limiting; thermionic amplifiers. - Means for reducing or eliminating interference from statics or other disturbing impulses' in wireless or like tuned signalling systems, comprises two receiving circuits or two branches of a single circuit, one circuit being arranged to receive and pass both desired signals and disturbances, the other circuit to eliminate the desired signals and to pass only the disturbing impulses, the output of the two circuits being so combined that the disturbances are eliminated. Fig. 1 shows one form of the circuits, the receiving-aerial 1 being earthed through resistances 33, 34, loading-coil 2, and a series combination of inductance 3 and capacity 4 tuned to the signal frequency. The receiving-circuit proper S is connected between earth and the upper end of the loading-coil 2, and comprises a number of high-frequency amplifiers 7, 9, 10 with their circuits tuned to the signal frequency, and a detector valve 11. The balancing circuit B is connected across the elements 3, 4 and therefore receives a minimum of energy of the signal frequency. It comprises a number of valves with aperiodic circuits interconnected by resistance-capacity couplings. An intermediate valve 20 has a capacity 27 and inductance 26 in series in its grid circuit, tuned to signal frequency, and consequently further reducing the transfer of energy of this frequency. Leak resistances 5, 28 shunt the tuned circuits 3, 4 and 26, 27 in order to allow the grids to discharge. The last valve 23 has its grid circuit tuned to signal frequency and its grid is given a suitable negative, potential by a potentionmeter 29. to enable this valve to act as a rectifier. The plate circuit of the valve 23 comprises a high-tension battery 30 and an impedance 13 forming part of the grid circuit of the last valve 11 of the receiving-circuit S. By suitable adjustment of the magnification of the two circuits S. B, the static component of the currents in the circuits of the valve 11 marybe neutralized. The impedance 13 may be variable and may be in parallel with a condenser. or may include a tuned circuit. The aerial coil 2 may be of high resist. ance, but the part 3, 4 should be of smafff resistatice. The system shown in Fig. 2 is modified for reducing the effect of interfering signals. The signal-receiving circuit S is similar to that described above, except that it is loosely-coupled to the aerial inductance 2. The balancing circuit B is shown in two sections, the lower section being a continuation of the right-hand end of the upper section. It is connected across the coil 2 and resistances 33, 34, these elements being included in the grid circuit of the first valve 37. The plate circuit of this valve includes resistance 38 and inductance 39, and the plate circuit includes inductance 45 and capacity 46 in parallel, with resistance in both branches. The plate is connected through a condenser 50 to the grid of the next valve 49, which has & high resistance in its plate circuit. The first three valves produce amplification with very flat tuning. The grid circuit of the next valve 53, however, comprises an inductance 54 and a series condenser 55 tuned to the signal frequency 1 and consequently a minimum of energy of that frequency passes to this valve. The tuned circuit 54, 55 is bridged by a leak resistance 56 to provide a conductive grid circuit. The valve 58 produces non-selective amplification, and its plate circuit is coupled inductively to an adjustably-damped circuit 63, 64 tuned broadly to an interfering frequency. This tuned circuit is connected in the grid circuit of the next valve 61, thereby emphasizing to an adjustable degree the interfering oscillations. The next valve 68 has in its grid circuit an inductance and capacity in series, shunted by a resistance and tuned to the frequency of a second interferring signal, the effect of which is thereby reduced. The plate circuit of the valve 68 includes an adjustable resistance 74 shunted by a condenser, and a coil 73 coupled to a coil 79 is in series with a resistance 78 and both are shunted by a condenser 77. This arrangement emphasizes low frequencies relative to high frequencies. An opposite effect is produced by the next valve 80 the grid circuit of which has a shunt comprising a condenser 82 and resistance 81. The plate circuit of the valve 80 has a resistance-capacity coupling to the grid circuit of the valve 85, which has an inductance 87 and series condenser 88 tuned to the signal frequency and therefore tending further to reduce energy of this frequency. A leak resistance 89 shunts the tuned branch 87, 88, and an adjustable, series resistance 90 is provided to enablle the right proportion of the interfering signals and statics to be passed on. The following valve 91 has in its grid circuit two seriee-tuned branches 93, 95 serving respectively to reduce currents of the signal freuency, and of the frequency of an interfering station which may have become unduly prominent. The next valve 103 has its grid circuit tuned so as to reduce further the signal, and the tuned branch is shunted by a low resistance of the order of tens of ohms, so as to emphasize lower frequencies. The last valve 104 of the balancing circuit B is tuned to the signal frequency, and its grid is given a negative potential to enable the various frequencies to be rectified. The plate circuit of this valve includes an impedance 13 connected in the grid circuit of a trigger valvd 35 coupled to the output end of the receiving circuit S and operating as described in Specification 156,330. The intervalve connections of the receiving-circuit S may comprise capacity couplings between plate and grid, and tuned shunts may be provided to by-pass one or more interfering frequencies. The grid circuit may comprise an inductance which with the coupling condenser forms a series tuned circuit for the signal frequency. High potentials across the inductance will be caused by currents of signal forequency, and these potentials affect the grids and cause this frequency to be selectively amplified. In a modified arrangement a frame aerial is employed, and the receiving-circuit S and balancing circuit B are similar to those of Fig. 1, except that reaction is employed between the plate circuit of the valve 20 and the grid circuit of the valve. 18. The reaction circuit includes several amplifying valves, one or more of which is ar ranged to by-pass the signal frequency, and the plate circuit of the last valve includes a phasechanging device comprising two coils set-up at right angles and carrying currents in quadrature. The grid coil of the valve 18, on which the. reaction is effected, is adjustably mounted within the perpendicular coils. The valves in the reaction circuit may be provided with other selective devices. The reactive connection may be replaced or supplemented by a connection from an intermediate valve in the balancing-circuit to an intermediate valve in the signal circuit. In the modification shown in Fig. 5, the balancing-circuit is merged into the reaction circuit of the signal receiver. The aerial 1 has distributed resistance 33, 34 and a tunirg-coil 2 and is directcoupled to a series of aperiodic amplifying valves 122 - - 126, and thence to two valves 129, 130 with grid circuits tuned to the signal frequency. The last valve 130 has sufficient negative potential applied to its grid by a potentiometer 132 to enable it to rectify the signals and render them audible in a telephone 14. Reaction is provided between the output of the valve 125 and the imput of the valve 123. The reaction circuit includes a number of valves 109 - - 111, and is similar to that described above, with the result that the energy returned into the grid circuit of the valve 123' by the coupling 128, 124 is substantially free from the signal frequency. A phase-adjusting device may be used, and the reaction is so arranged as to have a neutralizing instead of an amplifying effect. As the reaction circuit transmits only disturbing impulses, such impulses are. substantially neutralized and the signals are not affected. The currents in the balancing-circuits B of Figs. 1 and 2 need not be rectified before cornbinaton with the currents in the receiving-circuit S, or both methods of counterbalancing may be employed simultaneously. Also there may be one or more stages of amplification, before the balancing circuit divides from the receiving circuit.