GB592789A - Improvements in or relating to arrangements for selecting electric pulses according to duration - Google Patents

Abstract

592,789. Pulse modulation. STANDARD TELEPHONES &. CABLES, Ltd. June 26, 1945, No. 16326. Convention date, May 15, 1943. [Class 40 (v)] A circuit for selecting pulses of a specified duration from a train of pulses, comprises a tuned circuit, the period of which is twice the specified duration, which is shock excited by the edges of each pulse and produces an undulation of maximum amplitude following the trailing edge of a desired pulse which is discriminated by a clipping circuit. The pulses 20 ... 23, Fig. 2 (a), are applied to a limiter valve 12, Fig. 1, the anode circuit of which comprises a load resistance R and tuned circuit 25. Connected across the latter is a valve 30 the control grid of which is connected to the anode of valve 12. The voltage wave at the junction of resistance R and circuit 25 is fed to a clipper stage 40 through lead 36. The edges of the amplitude limited pulses b, Fig. 2, in the anode circuit of valve 12, shock excite the tuned circuit 25. The leading and trailing edges 51, 55 respectively of the pulse corresponding to a desired pulse 20, produce negative and positive undulations 52, 56, curve c, respectively at the end 26 of circuit 25. The undulation 56 adds to the damped positive undulation 53, which normally follows undulation 52, to produce the resultant 60. The valve 30 is blocked by the input pulse during the negative undulation 52 and is non-conductive for positive voltage excursions such as 60. For the following damped negative undulations 54, 57, however, the valve 30 becomes conducting and suppresses any further shock-excited damped oscillations. Pulses of duration other than the desired value produce resultant positive undulations 61, 62, 63, of smaller amplitude than that of undulation 60 as shown in curve c, Fig. 2. The output of the tuned circuit 25 is clipped at level 80 by valve 40 so that the final output at point 41 comprises pulses 60a, Fig. 2 (d), corresponding to input pulses 20 only, which may be subsequently shaped for utilization. Specification 581,068 is referred to.