Patent GB-640504-A (GB)
Title: Improvements relating to radar receiving apparatus
IPC: G01S1/02
Filed: 1946-07-09
Abstract: 640,504. Radiolocation; pulse and sawtooth generating circuits. SHAND, G., and METROPOLITAN - VICKERS ELECTRICAL CO., Ltd. July 9, 1946, No. 20511. [Classes 40 (vi) and 40 (vii)] Relates to pulse radar equipment in which a normally blocked receiver is rendered operative by a gating pulse to operate warning apparatus when echoes are received from objects within predetermined range limits defined by the timing and duration of the gating pulse. According to the invention the gating pulse is generated by a flip-flop circuit triggered by the trailing edge of the output from a further flipflop circuit which is triggered by the transmitter pulsing circuit. The invention is described as applied to a marine navigational radar with a P.P.I display in which an aural or visual warning is produced when the reflecting objects are within range limits of 1¢ to 3 miles and means are also described for producing a positive indication that the set is functioning properly in the absence of echoes from such objects. As shown in the Figure, positive synchronizing pulses from the transmitter are inverted at V1 and applied to trigger a cathode-coupled flip-flop V2 which produces across the cathode load a positive delay pulse, the trailing edge of which triggers a second cathode-coupled flip-flop V3 which produces a negative gating pulse across the anode load R8 of V3B, the operation of the two flip-flops being as described in Specification 617,788. The gating pulses are applied to a gate valve V4 of the type disclosed in Specification 614,221 together with suitably amplified and limited positive echo pulses from valves V10-V13 and the positive gated echo pulses appearing across the anode load of V4A trigger a cathode-coupled flip-flop V5 to produce negative pulses of increased duration across the cathode load which are applied to V8. The cathode of V8 is directly coupled to the cathode of V7 which is in series with a blocking oscillator V6. V8 is normally conductive so that V6 is cut off but on receipt of a negative pulse from V5 the cathode potential of V8 is reduced and V6 becomes operative rapidly charging condenser C8 which then discharges slowly _(discharge time “ second) through the pentode V7 which has its Miller capacity increased by C9. The sawtooth output from the anode of V7 is applied to V9 whose cathode bias is such that the valve is rendered conductive during the first half of the applied sawtooth to operate a relay B which energizes an audio-frequency oscillator, Fig. 3 (not shown), whose output is applied to a loudspeaker. Thus when an echo is received within the duration of the gate pulse, an audiofrequency note of # second is produced which repeats every “ second. In order to indicate that the set is functioning in the absence of gated echoes, a further relay A is provided, Fig. 2 (not shown), which is periodically operated by the rotating aerial to close contact Al and thus reduce the duration of the delay pulse generated by V2 so that short-range sea echoes are received within the gate period to produce a " warning note " of diminished intensity. In a modification, Fig. 4 (not shown), the valves V6-V9 are replaced by a flip-flop which operates the relay B and in Fig. 5 (not shown) the flip-flop V5 is replaced by an inverter valve. A visual warning indicator, e.g. a lamp, may be employed in addition to or in place of the aural warning. Specification 617,177 also is referred to.