GB583262A - Improvements in the production, selection and demodulation of electrical pulse trains - Google Patents

Abstract

583,262. Pulse selecting systems; frequency dividers. STANDARD TELEPHONES & CABLES, Ltd., and EARP, C. W. Nov. 26, 1943, No. 19828. [Class 40 (v)] Regularly repeated pulse signals are selected by a gate circuit under the control of pulses derived from a stabilised multi-vibrator which is under the control of the pulses. The gating valve is normally blocked, but is opened by pulses from the multi-vibrator. The arrangement may be used for selecting to avoid interference or as a frequency divider. Fig. 1 shows a multi-vibrator V1, V2 to which the impulses are applied directly while the impulses are applied through a delay network DN, and pulse inverting device ID to the control grid of the gating valve V3. Gating pulses are derived from the cathode resistance R3 in the multi-vibrator circuit and applied to the suppressor grid of the gating valve. When short gating pulses are required, a differentiating circuit may be included between the cathode resistance R3 and the suppressor grid of the gating valve. The pulses obtained across R3 may be used as the output instead of the anode of the gating valve V3. The gating valve may be used as a demodulator using triangular pulses in the case of time phase modulation. The Specification shows that when short gating pulses are required, a high degree of stability is necessary in the multi-vibrator. Such stability may be obtained by including a resonant circuit of small damping in the circuit to produce ringing and thus superpose a sine wave on the saw-toothed wave generated. Such a circuit may be included between the terminals 5, 6, but to ensure adequate stability, two such circuits may be used and connected in series and be tuned one to a multiple, say 10, of the multi-vibrator frequency, and the second to a multiple, say 3, of the frequency of the first. Further circuits tuned to other multiple frequencies may be used and the circuits may alternatively be connected in series, or some may be in series in the anode circuit of one valve and some in the anode circuit of the other valve. The elements R2, C2 determine the duration and the elements R1, C1 the length of the pulses. The synchronizing pulses may be applied in negative sense in which case the leading edge of the pulse is effective, or in positive sense in which case the trailing edge of the pulse effects synchronization. In the latter case, the resultant lag in the gating pulses enables the delay circuit to be dispensed with, and at the same time the pulse inverting device is rendered unnecessary, but the multi-vibrator is adjusted to operate at a frequency a little higher than that of the incoming pulse frequency instead of a little lower. In a modification, Fig. 6 (not shown), in which the input is applied only to the gating valve, the multi-vibrator is synchronized by being fed in series with a resistance shunted by a large condenser arranged in the anode circuit of the gating valve. In this way the anode potential of the multi-vibrator is controlled by the gating valve and produces the required variation in frequency of the multi-vibrator as determined by the long term variation caused by lack of coincidence between the multivibrator and the incoming pulses. Specification 583,117 is referred to.