Patent GB-1124989-A (GB)
Title: A radar installation comprising a digital evaluating circuit
IPC: H02H1/00
Filed: 1965-11-24
Abstract: 1,124,989. Pulse radar. TELEFUNKEN PATENTVERWERTUNGS G.m.b.H. 24 Nov., 1965 [24 Nov., 1964], No. 49894/65. Heading H4D. The invention relates to the checking of a pulse radar system of the type wherein echo pulses are only accepted when above a certain amplitude and produce a pulse for display and/ or processing when the same accepted echo pulse occurs a certain minimum number of times in a certain number of consecutive pulse cycles. The above echo pulse checking in amplitude and consistency is performed in circuit A. A pulse train t is commenced by each transmitted pulse R (or by a pulse delayed therefrom), and defines range increments. The pulse train is fed to a binary counter EZ which then reads the range being instantaneously swept. Two incidence gates K1 and K2 are connected to counter EZ and give outputs when the counter reads the maximum range and three, respectively. A binary counter PZ is fed with the transmitted radar pulses and so reads the number of the pulse being transmitted starting from 1, going up to 32, and then back to 1 &c. Circuit A is designed to pass a pulse to output AK only if echos at the same range of sufficient amplitude are received from five or more consecutive repetition periods. A gate Kn is thus applied to the output of counter PZ and controls a bi-stable circuit IF, such that for periods 32, 1, 2, 3, 4, the output of circuit IF is 1-for periods 5 to 21, the output of circuit IF is 0-for periods 22, 23, 24, 25, the output of circuit IF is 1, and from periods 26 to 31, the output of circuit IF is 0. The output of gate K1 and of circuit IF are connected to AND gate K3, such that gate K3 gives an output at the maximum range on repetition periods 32, 1, 2, 3, 4 and on repetition periods 22, 23, 24, 25. Circuit A, under test, should give an output at AK for the first group of outputs, but should give no output for the second group of outputs. The output of circult A occurs on the fifteenth repetition period after that producing the last of the five input pulses thereto, and at a range greater by three increments than that of the input pulses. Thus the circuit, if working correctly should, in response to the pulses on repetition periods 32, 1, 2, 3, 4 at a maximum range, produce an output pulse on repetition period 19 at the third range innercurrent (count of three in EZ). A gate Km connected to counter PZ causes a bi-stable circuit RF to change from its normal 0 state to a 1 state during the 19th repetition period. This 1 pulse is fed to one input of AND gate K4, and, as an inhibiting pulse, to one input of AND gate K5. The output of circuit A is fed as an inhibiting signal to the second input of gate K4 and the output of gate K2 is fed to the third input. Thus, if the circuit A operates correctly, gate K 4  is inhibited. If it does not however, the gate produces an output which is fed via OR gate D to an alarm counting circuit AF connected to a warning light AL. Similarly gate K5 will produce an output if an erroneous echo appears at the third range increment, on any repetition period other than the 19th. If the conditions for output of circuit A are changed, the ouput conditions of gates Kn and Km are also changed.