Patent GB-1189171-A (GB)
Title: Improvements in or relating to Echo Sounding Apparatus
IPC: G01S7/534
Filed: 1967-05-05
Abstract: 1,189,171. Echo sounding; switching circuits. ELECTROACUSTIC G.m.b.H. 5 May, 1967 [5 May, 1966], No. 21133/67. Headings H3T and H4D. [Also in Division G5] A stationary image of echoes from a selected partial range is obtained on the cathode-ray tube (C.R.T.) display of an echo sounder by recording the echoes on two magnetic tracks on a storage drum alternately and displaying echoes reproduced from one track while the other track is being recorded or erased. In the Fig. 4 embodiment oscillator RGN (20 kc./s. or 30kc./s.) is triggered by pulse generator TG to provide pulses for transducer Schw and echo pulses are frequency changed in ring modulator M to 10 kc./s. which is easier to record magnetically. The amplified 10 kc./s. signals pass via an electronic switch U 1 , which changes over every echo sounding cycle, to either of two recording heads K 1 A 1  or K 3 A 2  which scan tracks on a magnetic drum having a rotation time just greater than the duration of the selected partial range (e.g. 20 m.sec.). Erase head K 2 L 1  or K 4 L 2  is energized, via changeover electronic switch U 2 , at the same time as the associated recording head K 1 A 1  or K 3 A 2  respectively. The recorded echoes are thus those occurring in the 20 m.sec. prior to changeover of switches U 1  and U 2 . 16À5 kc./s. tone bursts, recorded at the changeover of switches U 1  and U 2  on tracks Sp<SP>1</SP> 1  and Sp<SP>1</SP> 2  by means of record heads K 2 A<SP>1</SP>1 and K 4 A<SP>1</SP>2 and follow-up erase heads K 1 L<SP>1</SP> 1  and K 3 L<SP>1</SP>2, are reproduced by heads K 5 W<SP>1</SP>1 and K 6 W<SP>1</SP>2 to provide trigger pulses for initiating the sawtooth timebase sweep (Y-deflection) of display CRT, K, and the recorded echoes are fed to the X-plates of the CRT from playback head K 5 W 1  or K 6 W 2  via switch U 3  which changes over in synchronism with switches U 1  and U 2 . To lock the display to the sea-bed echo, switch S 1  is set on contact B so that the rectified sea-bed echo from unit VGR1 trips cascaded bi-stables BM 1  and BM 2  and hence causes switches U 1 , U 2  and U 3  to change over. To lock the display instead to a preset depth, switch S 1  is set on contact F so that BM 1  is tripped by a pulse delayed from the instant of the ultrasonic transmission by delay circuit VF. For either method of locking the display, BM 1  is reset by a pulse from a delay monostable MM 1 . In a second embodiment (Fig. 1, not shown), the magnetic tracks Sp<SP>1</SP>1 and Sp<SP>1</SP>2 are omitted and the CRT timebase sweep is initiated by either the sea-bed echo (the strongest echo) or, when S 1  is set on contact F and no sea-bed echo is recorded, by a trigger pulse provided by a gated oscillator (O 3 ) and mixed in with the echo signal applied to switch U 1 . Circuit details.-The switch U 1  (Fig. 10) comprises two diode pairs Gr1, Gr2 and Gr3, Gr4 which are made conducting respectively by application of 0 or -15V to terminal 22 when bi-stable BM 2  is in its tripped and reset states. The echo signals at terminal 29, after amplification in emitter follower T 1 , are thus passed to either one of the push-pull amplifiers T 2 , T 3  and T 4 , T 5 . The switch U 2  (Figs. 12 and 13, not shown) is similar to U 1 . The switch U 3  (Fig. 15) similarly comprises diode pairs made conducting to pass recorded echo signals from either of two playback amplifiers T 1 , T 2  to further amplifier stages T 3 , T 4 , T 5 .