GB596654A - Improvements in or relating to pulse modulation communication systems - Google Patents

Abstract

596,654. Pulse-generating circuits. STANDARD TELEPHONES & CABLES, Ltd., CHATTERJEA, P. K., and BENEY, J. K. Dec. 20, 1944, No. 25593. [Class 40 (v)] A multi-vibrator circuit for producing pulses of variable duration is controlled by a saw-tooth wave-form which initiates regenerative action during the fly-back period to,form the leading edge of the pulse, while variable biassing means determine the instant at which regenerative action occurs in the reverse sense to form the trailing edge of the pulse. Fig. 1 shows a double-triode valve arranged as a multivibrator with a saw-tooth waveform applied at terminal 25. At the termination of the flyback, potentiometers 18, 19 hold their associated grids near cut-off and saturation respectively, and as the saw-tooth wave form increases from zero, the fall in voltage at anode 5 is kept small by the action of common cathode resistor 8 until the potential at grid 4 is lowered by reaction through capacitor 24 to the point where conduction becomes sensitive to grid voltage changes. Regenerative action then sets in to drive the 2nd section of the valve rapidly beyond cut-off and this condition persists until the fly-back stroke on grid 3 initiates regenerative action in the reverse direction to form the leading edge of the next pulse. Negative pulses appear at terminal 29 and positive pulses of an inferior form may be taken from anode 5. Biassing potentials at grids 3, 4 determine the pulse width which may be pre-set by potentiometers 18, 19 or time modulated by applying oscillatory signals to terminals 32 or 35. A differentiating network 30, 31 may also be included to give pairs of short-marking pulses with modulated separation. Specification 596,638 is referred to.