GB666896A - Improvements in and relating to electric oscillation generators - Google Patents

Abstract

666,896. Testing telegraph signals. BRITISH TELECOMMUNICATIONS RESEARCH, Ltd., and BEAUFOY, R. March 22, 1950, [April 5, 1949], No. 9279/49. Class 40 (iii). [Also in Group XL (c)] In an oscillation generator of the regenerative resistance-capacity type, oscillations are set up by a start signal rendering the feed-back operative, and are terminated by a stop signal removing the feed-back; and means are provided for producing a datum D.C. potential at the oscillator output when in the stop condition. The generator may be used in measuring the duration of signal elements in typeprinting telegraphy. In Fig. 1, the oscillator comprises two valves 10, 11 with their cathodes earthed through a common resistor 12, and with the anode of the valve 11 backcoupled to the grid of the valve 10 through a resistance-capacity network 13 ... 16. Frequency control is effected by varying the capacities or the resistors of the network either continuously or in steps. Quadrature phases are taken off from the output terminals 21 ... 23, and positive bias is applied to the grid of the valve 10 by a source GB+ and an adjustable potential-divider 17, 18. Start-stop control is applied across the terminals 19, 20 of the network resistor 13, an open circuit allowing oscillation and a short-circuit causing immediate cessation. In the latter condition, a D.C. voltage applied across the terminals 19, 20 provides datum potentials across the terminals 21, 22, 23. Alternatively, start-stop signals could operate a switch between the anode of valve 11 and the condenser 15. In a modified oscillator, Fig. 2, the valves 10, 11 have their anodes connected respectively to the grids of cathode-follower valves 26, 27 which have their cathodes connected through condensers 151, 15111 to opposite sides of a phase-shift network 13 ... 16 similar to that of Figure 1. Opposite terminals 23, 22 of the network condenser 16 are connected to the grids of the valves 10, 11 and output is taken from the anodes to terminals 221, 231. The quadrature phase taken across the terminals 22, 21 of the network resistor 14 is applied to the grids of a valve pair 31, 32, the anodes of which feed the output terminals 21<SP>1</SP>, 22<SP>11</SP>. Start-stop control is effected at the terminals 19, 20 of the network, as in Fig. 1. Each valve pair 10, 11 and 31, 32 have their cathodes earthed through resistors, and inter-connected by adjustable resistors 33, 36. Fig. 3 shows the start-stop control. Two triodes 40, 41 with reciprocal back-coupling each include a resistor 42, 43 in the cathode lead. A positive start signal applied at 44, 45 to the grid of the valve 40 opens that valve and so causes the valve 41 to be blocked, giving zero voltage at the cathode of valve 41 and positive voltage at the cathode of valve 42. The rectifiers 38, 39 connected to the respective cathodes thus present an open-circuit at the network terminals 19, 20. A negative stop signal applied to the grid of the valve 40 blocks that valve and opens the valve 41, causing the cathode of valve 40 to assume earth potential, and the cathode of valve 41 to become positive. A short-circuit is thus provided at the network terminals 19, 20 and oscillation ceases. In this latter condition a D.C. voltage across the terminals 19, 20 provides a datum potential across the condenser 16 and zero potential across the resistor 14 of the phasing network of Fig. 1. These potentials are amplified and appear at the output terminals 211, 22<SP>1</SP>, 22<SP>11</SP>, 231 of Fig. 2. The datum potential may be made equal to the oscillation amplitude across the condenser 16, so that the oscillation starts at maximum amplitude in one phase and zero amplitude in the other. In modified forms of Fig. 3, a further rectifier is connected between either of the cathodes and the network terminal 22, Figs. 4 and 5 (not shown). The short-circuit across the terminals 19, 20, Fig. 1, may be provided by a battery switched in and out by the start-stop signal, Fig. 6 (not shown). For measuring distortion in teleprinter signals, the apparatus may function by causing a time base to start at the commencement of a signal and to stop at the end of the signal, so that the duration of each signal can be measured and distortion therein readily ascertained.