Patent GB-785001-A (GB)
Title: Improvements in and relating to echo-ranging and the like
Inventor: HOPKIN PETER ROY
IPC: G01S7/04
Filed: 1955-01-25
Abstract: 785,001. Echo sounding and distance measuring apparatus. KELVIN & HUGHES, Ltd. Jan. 18, 1956 [Jan. 25, 1955], No. 2237/55. Class 118 (2). [Also in Group XL (c)] In a mobile pulse-echo system for displaying or record. ing echoes from a distance zone fixed relative to a reference object producing an echo of large amplitude and located at or beyond the farther limit of the zone, the duration of the display or recording timebase corresponding to said zone, the timebase is triggered by the echo from said object and the echo signals applied to the display or recording device are delayed by a time interval corresponding to the distance between the inner edge of said zone and said reference object so that the positions of displayed images of other objects fixed relative to said reference object does not change when the distance between the transmitter and said reference object changes. The invention is described as applied to a sonic fish locator, the reference object being the bed of the sea, but it is also applicable to flaw detectors (the reference object being the rear surface of the body under test) and to pulse radars (the reference object being a coastline). As shown in Figs. 1 and 2, the pulse output (a), Fig. 2, from a generator 11 triggers a delay circuit 12 giving a pulse output (b) whose trailing edge triggers a pulse generator 13 coupled to a transmitting transducers Tr. Echo signals from the receiving transducer Rx are applied through an amplifier 14 whose gain is varied during the recurrence period by waveform (c) from generator 15 and the large-amplitude echo 18, Fig. 2, (d) produced by the sea bed is selected by an amplitude discriminator 32 whose output (e) is applied to a time gate 33 opened by manually adjusted gating pulses (f) from generator 34 to reject "second time bottom echoes" 19, Fig. 2 (d), caused by multiple reflection between the surface and the bottom of the sea. An output (g) from gate 33 triggers a timebase generator 35 whose output (h) is applied to the X plates of a C.R.T. 81 and the echo signal output from amplifier 14 is also applied to the Y plates through an amplifier 30 and a 10 ms. delay device 22 comprising a rotating magnetic drum 25, recording, pick-up and erasing heads 24, 26, 28 and an erase and bias oscillator 27. In order to compensate for variations in the amplitude of the echoes due to changes in propagation conditions, the gain of amplifier 30 is controlled by a voltage generated in circuit 36 which is proportional to the amplitude of the output (g) from gate 33. In the modification illustrated in Figs. 3, 5 and 7 during each recurrence period the timebase executes a plurality of sweeps to display the same echo signals, suitably delayed, during each of these sweeps. In Fig. 3 (not shown) the output (e) from the discriminator 32 triggers a mono-stable multivibrator 38, Fig. 5, producing negative and positive pulses (k) and (m), Fig. 4, of duration equal to the system recurrence period minus about 25 ms., the negative pulse (k) being applied to cut off the erase and bias oscillator 27 and the positive pulse (m) being applied to gate on a series (h) of timebase sweep waveforms synchronized with the rotation of drum 25. In Fig. 5 the erase and bias oscillator 27 is controlled as in Fig. 3, but the timebase generator 35 is repeatedly triggered by the recorded bottom echo pulse as picked up by an additional head 42 whose spacing from the recording head 24 corresponds to a 2 ms. delay, the spacing between the main pick-up head 26 and the auxiliary head 42 corresponding to a delay of 10 ms. In Fig. 7 (not shown) the components 23-29, 42 and 43 of Fig. 5 are duplicated, the echo signals from the transmitterreceiver equipment 10 are applied continuously to the two recording heads, the output (e) from discriminator 32 is also applied to a time gate 33 which is opened by the positive portion of the waveform (k) from the multivibrator 38 and the output, Fig. 8 (g), from the time gate 33 triggers a bi-stable generator whose output, Fig. 8 (s), renders the two erase and bias oscillators 27 alternately operative and also controls switches which select the signal and trigger outputs from the drum 25 which is not being erased so that signals recorded on one drum during one halfcycle of waveform (s) are repeatedly displayed during the whole of the next half-cycle during which time signals are being recorded on the other drum. If the interval between successive transmitted pulses is varied in an irregular manner, Fig. 9 (not shown), such intervals may be less than the echo times of objects within the selected zone since only echoes within the selected zone will produce a stationary display. The magnetic drum 25 may be replaced by magnetic tape, an acoustic delay device or an electrical delay network, repetition of the display signal being produced by repeated reflection or by feedback.