Patent GB-731265-A (GB)
Title: Improvements in or relating to electrical impulse generators
IPC: H03B29/00
Filed: 1952-04-16
Abstract: 731,265. Electromagnetic interrupters. PURDUE RESEARCH FOUNDATION. April 16, 1952 [April 17, 1951], No. 9586/52. Class 38 (5). [Also in Group XL (c)] An impulse noise generator intermittently producing the equivalent of a flat continuous radio-frequency spectrum comprises an openended pulse generating line d (Fig. 8) which discharges through a series resistance Rs equal to about three-quarters of the characteristic impedance of the line when finely adjustable contacts between Vs and Rs, driven by a pulsed magnetic driver, close to complete a discharge path of steep voltage wavefront through the contacts and resistance Rs from a previously charged portion of the line, the pulse output being taken across the resistance. The series discharge resistance Rs may be the impedance of an output transmission line or wave-guide. The contact driver may comprise a speaker-type balanced armature or other magnetic driver N-S energized at a rate, e.g. 6000 cycles per second, by pulses from a multi-vibrator, and driving a diaphragm 38 (Fig. 14) bearing a movable contact 61 coacting with a fixed contact 61<SP>1</SP> connected to the central conductor 30 of a coaxial cable output line 30, 31. The periphery of the diaphragm 38 is connected to an insulated metallic ring 36 mounted within an annular folded-back portion of U - crosssection of the outer conductor 31 and the energy capacitively stored in this ring 36, the latter corresponding to line d in Fig. 8 is delivered to the fixed contact 61<SP>1</SP>. The movable contact is connected to the H.T. source through a decoupling and charging resistor 60 limiting the D.C. current which may be broken without arcing when the contacts separate. The output line conductors are separated by spacers 32 but connected at the charging end by a disc-type discharge resistor 33 (Fig. 14) corresponding to Rs (Fig. 8). The discharge line is externally threaded at 71 and the assembly is longitudinally adjustable between and detachable from end mounting plates 26b, 41 spaced by sleeves 43 by a differential screw mounting arrangement adjusted by a calibrated knob 74. End play is taken up by springs 98 bearing on a cross-bar 91 threaded on the assembly. The charging H.T. and driving pulses are supplied by conductors passing through the sleeves 43 from the front of the instrument, detachable cable connectors there connecting the conductors with the power and driving supply. The multivibrator pulses are fed through cathode followers to the cable feeding the magnetic driver. A further multi-vibrator may operate through a relay to reverse at intervals the polarity of the charge to minimize metal transfer at the contacts. The contact spacing is also finely adjustable by varying the D.C. bias current through the magnetic driver from the cathode followers. In a modification (Figs. 17-19A, not shown) the cross-bar 91 is forked at both ends and engages the sleeves 43 and the latter carry the spring taking up end-play, and the knob 74 carries a pin driving a concentric disc for clamping by a locking screw, and is prevented from making more than one revolution by the pin engaging an abutment. In a further modification (Fig. 21), fine adjustment of the fixed contact assembly is effected by a differential screw operated by a knob 74 and coarse adjustment by loosening the screws on a spring loaded clamping bar 141<SP>1</SP> so that the outer conductor alone can be rotated. A nut 248 with set-screw binds the outer conductor to the liner and central conductor.