Patent GB-601792-A (GB)
Title: Improvements in or relating to arrangements for shaping and selecting electric pulses
IPC: H04J3/00
Filed: 1945-11-09
Abstract: 601,792. Pulse modulation. STANDARD TELEPHONES & CABLES, Ltd. Nov. 9, 1945, No. 30042. Convention date, Aug. 19, 1944. [Class 40 (v)] A pulse shaping snd selecting arrangement comprises a resonant circuit having a period equal to twice the width specified for the shaped or selected pulses and control means to apply pulses either to be shaped or to be selected. In one embodiment, Fig. 1, a radio transmitter 110 and receiver 113 are _associated with a common aerial 111 through a T-R switch 40, which also connects a common pulse width shaper and selector 41 and clipper and amplifier 78, 79, either between the pulse generator and modulator 15 and transmitter 110 or between receiver 113 and demodulator 157. When switch 40 is in the transmit position, the pulses c, Fig. 3, from pulse modulator 15 are applied to the grid of limiter valve 45 in whose anode circuit is a resonant circuit 42 in series with a resistance 49. The resonant circuit period is equal to twice the desired pulse duration and it is shunted by a valve 65. The output pulses d, Fig. 3, from valve 45 shock-excite the circuit 42 to produce negative undulations 73, curve f, Fig. 3, the other following undulations being damped out by the shunt valve 65. The clipper valve 78 is biassed to cut-off at level 89 so that pulses from the resonant circuit applied to its grid appear at its anode as positive rectangular pulses 107, curve g, Fig. 3. The clipper valve 96 cuts off the pulses at a level 106 dependent upon that of the pulses of maximum amplitude and its output, curve h, is fed to the transmitter 110 to produce the R.F. pulses, curve i. When the switch 40 is in the receive position, the receiver 113 applies negative pulses, which may be of various durations and amplitudes, to the grid of valve 45, which acts as a limiter, so that positive pulses of constant amplitude appear at its anode. The negative undulations across the tuned circuit are greatest in amplitude when produced by pulses whose duration is half the period of the tuned circuit, Fig. 4 (not shown). These negative undulations of maximum amplitude are selected by the clippers 78 and 96 and passed to the demodulator 157. The variable clipper 96 may be replaced by a circuit 156 clipping at a fixed level. In a second embodiment, no T-R switch is employed, the pulse modulator and receiver outputs being mixed before application to the width shaper and selector and the output of the latter is fed to the pulse demodulator and transmitter. A blocking voltage, derived from the pulse modulator, disables the receiver for the duration of each transmitted pulse, Fig. 2 (not shown). In a further embodiment using amplitude modulated pulses, the transmitted pulses are generated by a multivibrator 252, Fig. 7, passed through the common width shaper and selector 41, pulse amplitude modulator 253 and transmitter 254 to the common aerial 111. The pulses aa, Fig. 8, from the output of receiver 113 are fed to the circuit 41 which produces pulses dd which correspond to pulses of the desired width only, are of constant amplitude and,occur after a delay T1 corresponding to the duration of the desired pulses. The pulses aa are also fed to a width selector 266 which includes no limiting or clipping circuits and produces the undulatory output ee which is added to the pulses dd in the mixer 264 and produces output ff. Circuit 264 is arranged to clip at the level 267, curve ff, and produce the desired amplitude modulated pulse output gg which is fed through an integrating device 271 to the reproducer 177.