Patent GB-646700-A (GB)
Title: Radio range-finding and locating systems
IPC: G01S7/282
Filed: 1944-10-17
Abstract: 646,700. Radiolocation. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. Oct. 17, 1944, No. 20102. Convention date, June 17, 1942. [Class 40 (vii)] In a pulse-echo distance measuring apparatus in which reference pulses generated in synchronism but delayed in phase with respect to the radiated pulses are brought into step with the pulses received from the remote reflecting object and the time interval between corresponding radiated and reflected pulses is determined by observing the difference in phase between corresponding radiated and reference pulses, a high-frequency oscillator feeds one frequency-dividing system to produce transmitter keying pulses at relatively low pulse recurrence frequency and, through a phase-shifting device, another frequency-dividing system to produce reference pulses at the same recurrence frequency, the pulses from the reflecting object and the reference pulses passing through a circuit which controls the phase-shifting device to maintain coincidence between the reference and received pulses. Referring to Fig. 1, a crystal oscillator 10 generates a frequency of 819.4 kc/s. which is divided by 200 in a three-stage frequencydivider system 11 to provide transmitter keying pulses of a recurrence frequency of 4.1 kc/s. Reflected pulses 17 from an object 14 are received by a receiver 16 and pass to a gate valve 21. Part of the 819.4 kc/s. output of the crystal oscillator 10 is passed through a phase shifter 31 to a second frequency dividing system 32 identical with 11 and the 4.1 kc/s. output of the system 32 is split between wave shapers 86 and 30. The wave shaper 86 forms suitable pulses to gate the valve 21. The phase of the echo pulses 17 with respect to the reference pulses 33 is determined in the manner disclosed in Specification 646,355 by means of a peak amplitude comparison system 34, 28, 29, 38, 39, 51, of which 38, 39, 51 consist of a balanced amplifier giving an output controlling a motor 54 which in turn controls the phaseshifter 31. The frequency dividing systems 11, 32, Fig. 3, comprise a chain of multivibrators 71, 72, 73 and 71A, 72A, 73A of conventional type. In order that the multivibrators 71 and 71A may lock in on the same cycle of the output of the oscillator 10 when the phase-shifter 31 is at zero phase shift, the grid of one of the valves of the pair comprising one multivibrator, namely, the grid of the valve 77, is connected to the grid of the corresponding valve, namely 77A, in the other multivibrator through a switch S1. Similar interconnections are provided between the other multivibrators of the two systems, the interconnections including the switches S2 and S3. The three switches S1, S2 and S3 are ganged as at 83. The phase shifter 31 is set for zero phase shift and the switches S1, S2, S3 closed for calibration at the start of the operation. To improve the stability of lock-in a tuned circuit 78 tuned to the frequency of the desired output may be included either in the plate circuit of the valve 77 as shown or in one of the grid circuits of the valves. The gate valve 21 is normally biassed and cut off by a battery 22. A switch 25 is provided in the gating pulse circuit which is normally in the full line position (Fig. 1). When moved into the broken line position, the switch breaks the gating pulse circuit and also removes the bias rendering the apparatus responsive to any received pulse, e.g. during searching.