Patent GB-644579-A (GB)
Title: Improvements in or relating to electrical timing systems
IPC: G01S1/02
Filed: 1946-12-09
Abstract: 644,579. Pulse frequency dividing circuits; radio navigation. SPERRY GYROSCOPE CO., Inc. Dec. 9, 1946, No. 36320. Convention date, Dec. 7, 1945. [Classes 40 (vi) and 40 (vii)] A circuit produces pairs of pulses at an adjustable repetition rate with an adjustable and accurately known spacing, particularly for use in a receiver for a hyperbolic navigation system such as " Loran." Adjusting pulse spacing, Fig. 6. The output of a 100 kc/s. crystal oscillator 201 is divided down and converted to a square waveform having a repetition frequency in the order of 25 c.p.s. in the stages 202 ... 207 and 211. This is fed through differentiating and fixed delay devices 212 and 214 (see below) to an output terminal 215 to form the reference pulse of the pair. The other pulse of the pair appears at terminal 231 and is generated with a desired delay by causing an edge of the square wave from device 211 to tip a flip-flop 213, having one stable state, into its unstable state, until a pulse derived from an intermediate stage in the frequencydivider via devices 218, 222 and 227 causes it to revert to its stable state, producing an output pulse in so doing. The period between pulses from devices 211 and 227 determines the first digit of the delay and is varied by converting the pulse waveform from the divider to a sine wave in device 218, varying its phase in device 222 and converting it back to a pulse waveform in device 227. The second digit of the delay is similarly selected by devices 217, 221 and 226, while the difference between the thus-selected delay and the desired delay is similarly introduced by means of devices 216, 219 and 225. A single delay selecting control 223 drives the phase-shifting devices 219, 221 and 222 through suitable gearing, a counter 224 gives a reading of the delay. Devices 212 and 214 give the reference pulse a fixed delay in the same way as devices 213, 228 and 229 delay the delayed pulse, so that the final reference pulse always coincides with a half-cycle of the waveform from the crystal oscillator 201. Adjusting pulse repetition frequency, Fig. 6. Coarse adjustment is effected by varying the division ratio of divider stage 206. Fine adjustment is effected by feeding back pulses from the final divider stage 206 to the input circuits of divider stages 203 and 204, so that the effective division ratio of each of these stages is reduced. Since this feed-back causes a transient shift in some of the intermediate divider frequencies, a delay circuit 207 is interposed between the output of divider stage 206 and square-wave generator 211 so that the latter is not triggered until disturbances have subsided. This delay device consists of a flip-flop having one stable state which is tripped into its unstable state by a pulse from 206, and back into its stable state by a pulse from divider stage 204, this latter change giving rise to an output pulse. Flip-flop circuits. Fig. 2 shows a cathodecoupled pair used for the devices 212, 214, Fig. 6, in which valve 71 is non-conducting until a pulse from device 211, say, unblocks it until capacitor 84 has charged sufficiently to allow valve 72 to conduct again, or, as is the case in use, until a pulse from frequency-divider stage 204, Fig. 6, brings about the reversion to the stable state by unbolcking valve 72. A similar circuit, Fig. 3 (not shown), is used for the devices 213, 228, 229. In the case of device 213, the grid potential of valve 71 is varied in accordance with the setting of the phase-shifter 222 so that the free unstable period is varied in accordance with the delay required, though it does not determine it. The Specification as open to inspection under Sect. 91 describes a frequency dividing circuit, Fig. 5 (Cancelled). In this circuit, a capacitor 129 is charged in steps through either of diodes 135 and 136 until the voltage across it is sufficient to overcome the standing bias on valve 121 whose anode circuit rises initially and then falls abruptly owing to the regenerative transformer coupling between grid and anode circuits, the abrupt fall in anode current giving rise to the output pulse. This subjectmatter does not appear in the Specification as accepted.