Patent GB-1259639-A (GB)
IPC: G01S3/808
Filed: 1969-12-05
Abstract: 1,259,639. Sonar; phase comparators; transistor pulse and gating circuits; gain control; cathode ray tube circuits. BENDIX CORP. 5 Dec., 1969, No. 59554/69. Headings H3A, H3T, H4D, H4R and H4T. A sonar receiving system comprises circumferentially arranged receiving transducer elements providing pairs of adjacent directional receiving beams, each pair of beams giving target bearing information over a respective angular sector, a cathode-ray tube (CRT) range/bearing display covering a 360 degrees reception field and having a spiral raster, a respective pair of narrow band receivers for each sector and whose signals are phase compared, and a scanning device for successively connecting the sector signals to the CRT. In the Fig. 1 embodiment the 360 degree field is covered by eight 45 degree sectors whose signals are processed by identical channels 14, 18, 20, 22, 24, 26, 28, 30. Channel 14 is fed from two transducer staves 10, 12 whose signals are converted at 78, 116, 150 to an I.F. frequency then squared by limiters 174 for application to phase comparator which gives an output voltage proportional to the phase difference (i.e. representing target bearing within the associated sector 1). The outputs of I.F. amplifiers 150 are summed on resistors 176, 178 to provide an A.G.C. control voltage and detected video signal in stage 118. Similarly, phase comparator voltages and video signals are derived from other transducer staves, in the other channels. 8 KHz master oscillator 48 synchronizes the CRT angular sweep with the sequential connection of the video signals from the different sectors to the CRT brightness control as follows. 8-Count ring counter 50 provides 125 Ásec. gating pulses for the video signals of the sector channels in turn and its one and five outputs trigger bi-stable 52 to produce a 1 kHz square wave. This square wave chops a ramp voltage initiated on transmission of an acoustic pulse and the resulting modulated ramp is filtered at 60 to give a swept amplitude sinewave which is resolved at 62 into X and Y deflection voltages, mutually phase-shifted by 90 degrees, for CRT 16. Synchro resolvers 64, 66 allow compensation respectively for magnetic variation and swinging of the transducer so that the display will be geographically oriented.  Gain control (Figs. 2 and 6).-Variable attenuation of a video pulse fed from input 80 (Fig. 2) to a frequency-changing mixer stage 96 via Darlington emitter-follower 82, 90 is provided by the shunt slope resistance of diode stacks 124, 126. An approximately linear relation between the attenuation and a gain control voltage (applied to the base of transistor 120 to vary the slope resistance) is obtained by the inclusion of biased diodes 136, 140 in shunt paths across emitter resistor 122. The gain control voltage is derived (Fig. 6) by rectifying the I.F. signal in voltage multiplier 256 and storing it on capacitor 262 (provided with Zener diode protection from over-voltage), the timeconstant for a decrease in the capacitor voltage being made smaller than the time-constant for a voltage increase by the inclusion of network 264, 266, 268. Phase comparison (Fig. 4).-The two I.F. signals of a Fig. 1 sector are squared in two similar limiter stages 186 then further shaped and differentiated in trigger stages 194, 196 to give voltage spikes, the positive-going spike from one I.F. signal being fed via diode 202 to trigger bi-stable 208 and the negative-going spike from the other I.F. signal being fed via diode 210 to reset the bi-stable. A voltage dependent on the mark/space ratio of the bistable output, and hence on the phase difference of the two I.F. signals, is obtained on capacitor 214. Gating circuits (Fig. 5).-Application of a gating pulse from the ring counter to the base of transistor 218 switches the transistor off; capacitor 233 then charges from a constant current source provided by transistor 222 and generates a ramp voltage which is compared in long-tail pair 236, 238 with a voltage proportional to the phase difference of the two I.F. signals of a Fig. 1 sector. On coincidence of the two voltages, current switches from the lower to the upper half of transformer 240 primary winding, generating a pulse (of width dependent on transformer construction) for switching the channel video pulse through transistor 244 to the CRT.  Cathode ray tube circuits (Fig. 8, not shown).- The chopped ramp voltage, from which the amplitude-swept sinewave is derived for conversion to X and Y spiral deflection voltages, is obtained by applying the voltages at the collectors of two transistors (324, 326) forming the bistable 52 of Fig. 1 as switching signals to the bases of two transistors (328, 330) for connecting an output stage (334) respectively to the ramp voltage and earth potential alternately.