Patent GB-594566-A (GB)
Title: An improved method and arrangement for modulating impulses
IPC: H03K7/08
Filed: 1945-03-16
Abstract: 594,566. Pulse modulation. PATELHOLD PATENTVERWERTUNGS- & ELEKTROHOLDING AKT.-GES. March 16, 1945, No. 6710. Convention date, March 16, 1944. [Class 40 (v)] In a pulse modulator, the position of at least one edge of each pulse relative to equidistant points is determined by values obtained at equidistant times from the modulating voltage curve. The modulator may produce duration modulated pulses with one fixed edge or two variable edges, or pulses of constant duration and variable timing. In the basic circuit, Fig. 4, amplitude modulated pulses of fixed duration and frequency, derived by interruption from the modulating voltage U1, unblock valve VL to allow condenser C to charge negatively, period t1, t2, Fig. 6. The charging current depends upon the pulse amplitude. After a fixed delay time t1, t3, valve VE is unblocked to discharge condenser C during period t3, t4, at constant current. The condenser cannot go positive, as the parallel rectifier G1 then becomes a short-circuit thereacross, the current in valve VE continuing to flow through the rectifier until the valve is cut off at time t5 at the end of the amplitude modulated pulse recurrence period T. Thus, a voltage pulse is produced across condenser C whose leading edge commences at the invariable time t1 and whose trailing edge ends at the modulated time t4, the times t2, t3 also being fixed. The discharging current is arranged to be always greater than the charging current. In one practical embodiment, the charging time t1, t2 is made equal to half the period T and the storage time t2, t3 is zero. Two charging valves VL, Fig. 7, are fed with out-of-phase amplitude modulated pulses and the associated discharge valves VE are controlled by the potentials developed at the anodes of valves VL. The two halves of the circuit have condensers Calpha, C#respectively and shunt rectifiers G1alpha, G1# respectively, G1alphahaving a series resistance Ralpha, and C# having a series resistance R# The voltages Ecalpha and Ec# developed across the condensers and the voltages Ealpha and E# developed across the resistances Ralpha, R# are shown in Fig. 8, the variable edges of the resultant pulses being designated V. By feeding voltages Ealpha and E# to a class-C amplifier, a rectangular pulse modulated on both edges is obtained. The condenser charging current can be reduced to a very small value, without reduction of the anode current of VL to zero, by producing a compensating current by the provision of a resistance between the screen grid and cathode of VE, Fig. 14 (not shown). In another embodiment, the con. denser C, Fig. 15, is charged through valve VL, and discharged through a grid-controlled gas discharge tube VGE at a time depending on the potential applied to its anode from the condenser, the triggering voltage U2 being of saw-tooth waveform and applied to its grid. In another embodiment, the modulation signal S4 is recorded on a film in the form of translucent strips St<1>, Fig. 17. The film is moved beneath a further translucent strip St<11> illuminated from above so that the time during which light passes through both strips simultaneously is determined by the height, of the strips St<1> and may be used to produce pulses in a photoelectric cell.