Patent GB-787075-A (GB)
Title: Improvements relating to electric pulse generators
IPC: H03K3/53
Filed: 1954-08-19
Abstract: 787,075. Generating high-frequency oscillations. GENERAL ELECTRIC CO. Aug. 19, 1954 [Aug. 24, 1953], No. 24199/54. Class 40 (5). An A.C. pulse of predetermined duration is produced when all the capacitances of a transmission line or network are discharged simultaneously, alternate capacitances being charged with like polarity and the intermediate capacitances with opposite polarity. The network may comprise lumped capacitances and inductances producing a sine wave pulse or a plurality of sections of coaxial cable, the output A.C. pulse being of rectangular waveform. In the latter case, the lengths of the sections may be so proportioned that the half-waves of one polarity correspond to the dots and dashes of a telegraphic code. In one embodiment, Fig. 1, the network comprises a series of filter sections comprising a series inductance and a shunt capacitance, one terminal of which is connected to the mid-point of the inductance so that the end sections of the series-connected inductances have a value L/2 and the intermediate sections a value L. Alternate capacitances C1 are connected through conductor 3 to one terminal of a D.C. source 4 and the intermediate capacitances C2 to the other terminal through conductor 5 and resistor 6. The network is correctly terminated at the ends respectively by a resistor 8 through blocking capacitor 9 and a load resistor 12 through blocking capacitor 13. Capacitances C1 and C2 are therefore charged to opposite polarities, their potentials being equalized by the equal shunt resistors 14, 141. When a key 7 is closed to connect together conductors 3, 5, a wave of alternating potential exists along the network which potentials tend to equalize, setting up oscillations in each section, the frequency of which is determined by the values of L and C1 or C2. The reflectionless terminations ensure that the pulse in the network has a duration corresponding to the electrical length of the network. The resistance 6 is chosen so that no pulse is produced when key 7 is opened. In a modification, the network is terminated at one end only, to double the duration of the pulse, Fig. 2 (not shown). The inductances may have ferrite &c. cores and the network sections may be T-section, #-section, constant-K and M-derived &c. Figs. 4, 6 (not shown). The sections may have inductances increasing in value towards the output end of the network, the capacitances being decreased in proportion to increase the uniformity of the amplitude of the oscillations in the load, Fig. 3 (not shown). In another embodiment, the distributed constants of a uniform coaxial transmission line produce a pulse, the oscillations in which are of square waveform. The conductors 3, 5, Fig. 7, are connected to alternate and intermediate isolated parts 35, 37 respectively of the line, the remainder of the circuit elements being the same as those of Fig. 1. The physical space requirements of such a generator may be reduced by coiling each of the parts 35, 37, the two sets of coils being arranged separately end to end with the shields of the individual coils in direct contact with one another, Fig. 9 (not shown). As the durations of the individual half-waves of the generated oscillation are determined by the lengths of the line sections, a code signal comprising dots and dashes may be generated by suitable selection of these lengths. The reactance of the blocking capacitor 13, Fig. 1, may be tuned out by a series inductance, Figs. 10, 11 (not shown), and the line or network may be terminated at both ends by a common resistance, Fig. 12 (not shown).