Patent GB-1084034-A (GB)
IPC: G01S13/22
Abstract: 1,084,034. Radio-ranging; cathode-ray tube displays. COMPAGNIE FRANCAISE THOMSON HOUSTON - HOTCHKISS BRANDT. Nov. 25, 1964 [Nov. 26, 1963], No. 48000/64. Headings H4D and H4T. In a cathode-ray oscilloscope display system for a dual-rate pulse radar system, the echo signals comprise first and second pulse trains having first and second pulse repetition frequencies (P.R.F's) F1, F2 respectively, the pulse trains alternating for equal periods of time at a third frequency F0 which is the highest common factor of F1 and F2, and the deflection voltages applied to the oscilloscope cathode-ray tube (C.R.T.) are such that the electron beam sweeps out a cyclic scanning curve having a line repetition frequency F1 and a frame scan repetition frequency F0, whereby the locus of displayed echoes from a single target due to pulses transmitted during one frame scan period intersects the locus of the displayed echoes from the same target due to pulses transmitted during an adjacent scan period to give a non-ambiguous indication of target range. The display system may also be used for monitoring a chain of separate radar stations transmitting at different frequencies. Production of signals.-In one embodiment, pulse trains having P.R.F's F1(= 576 c/s.) and F2(= 512 c/s.) are produced by generators (GE1, GE2) (Fig. 5) respectively and their coincidence at a frequency F0(= 64 c/s.) is detected by an AND-gate (9) (Fig. 1) in a logic circuit (LN). Coincidence pulses from AND- gate (9) trigger a bi-stable circuit (12) which opens gates (13 1 ) and (13 2 ) alternately so that a radar transmitter (RT) is triggered for equal times by the (GE1) and (GE2) pulses alternately. The transmitted signal thus comprises alternate trains of F1/F0 (= 9) pulses at a P.R.F. of F1 and F2/F0 (= 8) pulses at a P.R.F. of F2. C.R.T. timebase.-To provide the deflection voltages (Fig. 3) for spiral scanning of the electron beam, sine and cosine waveforms of frequency F1 are derived from signal generator (GE1) and are amplitude-modulated by a sawtooth waveform of frequency F0 from a generator (SG) (Fig. 1). C.R.T. trace.-Echoes of the transmitted signals are detected by a radar receiver (RR) and applied to a control electrode (CE) of the C.R.T. tube to intensity modulate the trace. For a stationary reflecting target, echoes from the nine pulses transmitted at a P.R.F. of F1 (equal to the line repetition frequency of the spiral scan, S, in Fig. 4) will occur as marks a, a<SP>1</SP> . . . along a radius OR. In the adjacent scan period, echoes from the eight pulses transmitted at a P.R.F. of F2 will appear as marks b, b<SP>1</SP> . . . along an expanded spiral #. The two loci OR, #, intersect at a point A whose radial and angular positions give a non-ambiguous indication of target range. Target marker.-Pulses having a P.R.F. of F0 are derived from a logic circuit (L<SP>1</SP>) (Fig. 5) (described in Specification 994,657) and are stretched and split to provide a bright-up marker M1 which can be moved along the spiral S, by manually adjusting a variable phase delay network (#) so that it straddles the intersection of the loci OR, #. Automatic tracking is selected by operating a change-over switch (44). As disclosed in Specification 994,657, a comparator (C) detects any phase-difference between target echo pulses and the pulses from logic circuit (L<SP>1</SP>) and causes a servo-motor (M) to adjust the network (#) so as to zero the phase-difference. Marker M1 then follows the target. At the same time, the switching between the transmitter triggering frequencies F1, F2 is made automatically dependent on target range as described in Specification 994,657, i.e. the transmitter is triggered at a P.R.F. of F1 unless the target range becomes an integral multiple of the critical distance at which an echo pulse would coincide with a transmitted pulse. Timebase modifications.-To indicate clearly the echo occurring at the intersection of the loci OR, #, the bi-stable (12) may energize a ringing oscillator (RO) (Fig. 1) to apply a small additional " wobble "-voltage to the deflection electrodes of the C.R.T. during the # scan. The intersection echo then appears as a circle with a dot in the centre. Alternative twodimensional scanning rasters having orthogonal line and frame scan components may be used, the frame component comprising a sawtooth scan and the line component comprising a sinusoidal scan (Fig. 6, not shown), a sawtooth scan (Fig. 8, not shown), or other cyclic function, and the target echo is indicated unambiguously in each case by the intersection of the linear locus with a locus which is an expanded form of the cyclic function. The C.R.T. deflection waveforms may be derived from generator (GE2) instead of (GE1).