Patent GB-1159440-A (GB)
Title: Improvements in Radioelectric Systems for Measuring Distance
IPC: G01S13/76
Filed: 1966-11-03
Abstract: 1,159,440. Radar; automatic phase control. COMPAGNIE FRANCAISE THOMSON HOUSTON HOTCHKISS BRANDT. 3 Nov., 1966 [5 Nov., 1965], No. 49406/66. Headings H3A and H4D. In a ground station-space craft system, wherein the ground station T transmits a telecontrol signal S 1  to the space craft V 1  which craft then replies with a telemetry signal S 2 , a low frequency reference signal IR is included in said telecontrol signal and the telemetry signal contains a cadence at said reference frequency phase locked to said reference signal as received at the space craft, whereby the distance to the space craft can be determined at the ground station by phase comparison of the reference signal and the received telemetry cadence. In the embodiment described a telemetry subcarrier of 384 c/s and a telemetry bit rate of 12 pps are used. In the space craft, Fig. 2, a clock 1 produces pulses at 6144 pps. These are passed via OR gate 2 and normally open AND gate 3, to a divider 4, whence the output 6 of an intermediate stage produces a signal defining said sub-carrier frequency and the last bi-stable stage 5 produces two square wave forms in antiphase, at 12 pps. The outputs 6 and 7 are fed to the telemetry transmitter and modulator. The reference signal at 12 c/s is extracted from the telecontrol signal by a transition detector 8, and 12 pps pulses appear on lines 801 and 802, respectively defining the beginning and the middle of the reference periods. The pulse signals on lines 801 and 802 are combined in OR gate 87 and are fed to a circuit comprising bistable circuit 89 and delay 80, which produces a control signal on line 803 on verification that the frequency of the combined pulses is 24 pps. These 12 pps pulses are fed, together with the control signal and the antiphase square waves at 12 pps, to a phase shift discriminator 9. Said discriminator comprises a bi-stable circuit 90 normally kept in a reset state by the pulses from the clock 1. When however the output of the divider 4 is in advance of the reference signal AND gates 97 and 98 are enabled by the square waves during the occurrence of respective pulses on lines 801 and 802, and pass said pulses a set input of the bi-stable 90. The next pulse from the clock 1 switches the bi-stable 90 back to a reset state and the resulting pulse output of the bi-stable is fed via delay 92 and OR gate 2 to the divider 4 to incrementally increase the divider output frequency. When the output of the divider 4 is delayed from the reference signal, AND gates 99 and 100 now pass the respective pulses of lines 801 and 802 to set a bi-stable 91 which is also reset by the next pulse from the clock 1. The resetting of the bi-stable causes the removal of the enabling signal from AND gate 3, whereby one pulse is subtracted from the input of the divider 4 and the output frequency thereof incrementally decreases. A circuit assembly 93/96 assures that the enabling signal is replaced. At the ground station Fig. 3, the 384 c/s subcarrier and the 12 c/s bit cadence are extracted from the telemetry signal and applied to respective inputs 21 and 22 of an AND gate 24. If a lower frequency signal, e.g. a word cadence, is present in the telemetry signal, this is applied to an input 23. The output of the AND gate is a signal at 12 c/s having the phase accuracy of the highest frequency input i.e. 384 c/s but the phase ambiguity of the lowest frequency input i.e. 12 c/s. The 12 c/s reference signal is fed via calibrating phase shifter 32 to the set input of bi-stable 28. The set state of 28 enables an AND gate 30 to pass clock pulses to a counter 29, each clock pulse so counted representing an incremental range. The set state also enables an AND gate 25 whereby the 12 c/s signals from gate 24 are fed to a cycle counter 27. This counter counts to N and then gives an output, where N is the known number of times the range represented by the period of the 12 c/s signal goes into the ground/space station distance. Said output enables an AND gate 26 whereby the N + 1th cycle is gated to reset bistable 28 and the gate 30 is thus closed. The count 29 thus represents said ground/space station distance.