Patent GB-1230221-A (GB)
IPC: G01S15/52
Filed: 1968-08-23
Abstract: 1,230,221. Cathode-ray tube displays; echo sounding. FRIED. KRUPP G.m.b.H. 23 Aug., 1968 [26 Aug., 1967], No. 40494/68. Headings H4D and H4T. Identification of the different traces, indicative of functions of a plurality of variables, produced on a cathode-ray display tube, is enhanced by producing the different traces with different brightness levels. As applied to an ultrasonic fish detector in which echo pulses from a receiver 1 (Fig. 1) in the form of an amplitude modulation of a high-frequency carrier wave are supplied via an amplifier 7 to the horizontal deflection plates of the display tube 3 to deflection modulate a time-base trace 6 produced by a sawtooth generator 5 controlled by a pulse generator 4 which drives a transmitter 2 (producing bursts of the high-frequency carrier wave), distinction between the various traces, i.e. the bottom echo a, the bottom rope of the trawl net b and fish inside the net c, is enhanced by producing such traces with different brightness levels. In the present embodiment, because it is necessary to set the gain of amplifier 7 at a high level in order that the low level echoes c from the fish be displayed with sufficient amplitude, the high level echoes a are of much greater amplitude than the echoes b and c. The amplitude of the echoes is more than sufficient to fill the display screen so that it is difficult to distinguish between this echo and echo b due to the trawl rope B which nearly fills the screen and the present embodiment operates to enhance distinction by causing echo a to be reproduced with a lower brightness than echoes b and c. This is achieved by rectifying the echoes from receiver 7 in rectifier 9 and applying a selected amplitude level, determined by potentiometer 11, to trip a Schmitt trigger 14 to the state in which stage 13 is cut-off so that transistor 18 conducts and by virtue of the potentiometer R16, R17 reduces the potential, derived from terminal 21, which is supplied to the brightness control electrodes of the tube. Thus by setting potentiometer 11 so that trigger 14 is tripped by the high amplitudes echo a the latter is reproduced at a much lower brighteness level than the echoes b and c distinction between which is easily made because of the marked difference in amplitude. The arrangement may, however, be extended to allow the latter echoes to be displayed with still different brightness levels. Fig. 2 shows a second embodiment in which echoes received from a target are reproduced with different brightness levels to indicate relative motion and the direction of such motion of the target with respect to the sounding apparatus (e.g. a vessel). In this embodiment a beat frequency of 1KH is produced by mixing in 40 the output of the pulse generator 4 (30 KH) with the output of an oscillator 41 (29 KH) and supplied to a L.P.F. 43 precisely adjusted to the frequency 1 KH. When relative motions occur the latter frequency changes + or - due to the Doppler effect and the phase of, the output of filter 43 changes. This phase change is sensed by a phase discriminator 49 the output of which controls a pair of transistors 34, 35 operating as D.C. differential amplifiers such that, depending on the direction of the Doppler change, either one or the other of the transistors is rendered non-conducting and a reverse bias voltage is therefore applied over conductor 25 or 26 to diodes 23 or 22, respectively. These diodes, when conducting, rectify an A.C. waveform having the same frequency as the received echo signals (produced in transformer 22 under the control of receiver 7) so that, depending on which is conducting, the Schmitt trigger is controlled to produce a brightness change either during the tracing of echoes above the horizontal time base, d, or below such trace, a. Thus the direction of relative motion is indicated by the side of the horizontal time axis on which the brightness change is produced. When there is no relative motion the display is produced with the same brightness, high or low, depending on the adjustment of potentiometer 11, on both sides of the time axis as shown at f. The invention may be employed to indicate the deviation and sign of the deviation of a target from a reference direction by utilizing the phase difference produced by two spaced receivers or groups of receivers and velocities may be measured by varying the frequency of oscillator 41 until uniformity between the received frequency and a comparison frequency is indicated by disappearance of the Doppler indication on the display tube. With this latter method the travel and drift velocities and the lift which a ship experiences through swell may be measured by varying the direction in which the transmitter radiates appropriately. The brightness control, in addition to the form described above, may be effected in a distinctive line pattern or area pattern which may indicate a further variable such as bearing.