Patent GB-594880-A (GB)
Title: Oscillograph apparatus for observing recurring electric pulses
IPC: G01S1/02
Filed: 1944-05-24
Abstract: 594,880. Radiolocation. STANDARD TELEPHONES & CABLES, Ltd. May 24, 1944, No. 10104. Convention date, Sept. 18, 1942. [Class 40 (v)] LAlso in Group XXXVI] Recurring pulses are expanded as viewed upon the screen of an oscillograph by producing a wave having recurring inclined portions and using these portions as sweep potential for the oscillograph, the inclinations of the inclined portions determining the degree of expansion of the pulse formed on the screen. The inclination may be changed by varying the amplitude or multiplying the frequency of the wave. A time modulator 12, Fig. 1, includes a full-wave rectifier, double differentiating circuits with limiters for generation of regular recurring pulses and time modulating circuits to modulate the pulses in pairs in respect of time in accordance with voice or other modulating signals. The time modulator 12 is provided with a voice modulator 14 and an antenna 16 for transmission purposes. A source 20 of sinuosidal energy 21 for the time modulator 12 and the pulses 22, 23 are generated therefrom in the time modulator. The modulation may comprise movement of one pulse relative to the other of a pair, or the pulses of a pair may move away from each other from their equally spaced positions. A cathode-ray oscillograph 25 enables the shape of the pairs of pulses to be examined or monitored and the percentage modulation determined. The sweep potential is provided by the sinuosidal wave 21 which is passed through a phasing device 26 and switches 27, 28 for passage through a gain control 30 by which the wave 21 may be amplified as desired. The output wave 31 is passed through a constant magnitude gate or double clipper 32, whereby a narrow strip is clipped from the centre portion of the wave form between the lines 33, 34. This results in a trapezoidal wave form which is amplified and applied to the plates 37, 38 of the oscillograph so that the inclined portions 35, 36 provide the sweep potentials. By keeping the gate amplitude constant and increasing the amplitude of the wave the sweep timing is decreased, thereby increasing the degree of pulse expansion. If the pulse pairs are centrally disposed in relation to the inclined portions 35, 36 the pulse shape 22 appears on the screen as shown in Fig. 3, the wave front 41 being first formed by the sweep line 35 and then the trailing portion 42. When the potential descends along the line 36 the return sweep traces the shape of the pulse 23, the pulse shape facing in the opposite direction to the pulse shape 22. Corresponding parts of the two pulses can be compared and monitored. When the pulses are time modulated towards one another the pulse shapes move together to the positions 22a, 23a. The percentage modulation may be determined by measuring the distance between the wave front traces of one of the pulses. For individual examination of the pulse shapes the phase of the wave 31 is changed by adjusting the phase shifter 26, the electron beam then tracing in a different time relation with respect to the pulses 22, 23, the pulse shapes of which are thereby separated as shown at 22b, 23b. The pulse shapes may be further checked by doubling the-frequency of the sweep potential wave by means of a frequency doubler 47 which may be introduced into the circuit by means of the switches 27, 28. The double-frequency wave has steeper-inclined portions thereby causing a greater expansion of the pulses. The pulse shapes may be further expanded by increasing the amplitude of the wave passing through the gain control 30. Different frequencies may be used for skipping alternate pulses when it is desired to examine individual pulses the frequency and plate adjustment being such as to have the return sweep occur between pulses. The effective sweeps may be so correlated as to provide mirror reflection of every fifth or seventh pulse &c. of a train of pulses, a frequency divider being employed instead of a frequency multiplier. For calibrating the screen of the oscillograph a scale calibrating circuit 60 receives and applies to the plates 61, 62 a sine wave 63 excited by the pulses 22, 23 but whose period is determined solely by the constants of the calibrating circuit 60. The number of screen squares 25a corresponding to a cycle of the wave 63 may thus be determined. Pulses generated in the time modulator 12 prior to voice modulation thereof may be used as the exciting pulse energy for the scale calibrating circuit by closing the switch 64. During calibration the time modulator may be disconnected from the plate 61 by opening a switch 67. A switch 68 enables the scale calibrating circuit to be temporarily connected. One of the pulse shapes of a pair may be removed in order to facilitate examination of the other by closing a switch 69 to connect in circuit a differentiating circuit 70. The sweep potential is differentiated and the resulting potential applied to the grid 72 of the oscillograph 25, thereby extinguisihing one of the sweeps, so that one only of the pulses 22, 23 appears on the screen. To trace the other pulse a switch 75 is operated to connect a phase inverter 74 in circuit. By providing the circuit 70 with a full-wave rectifier the pulses may be superposed similarly, thus brightening the outline. Fig. 7, shows a modification for the examination of any source of regularly recurring pulses. Pulse energy from the source 80 is applied to the plates 81, 82 of the oscillograph 85. The pulse energy is simultaneously applied from the source 80 to a translator circuit 83, which may comprise a shock excitable tuned circuit or a saw-tooth generator. In the latter case the pulses determine the initiation and termination of each saw-tooth. The output of the translator 83 is applied to a phase shifter 84, an amplitude gain control 86, and a doubleclipping device 87, the resulting wave being applied to the oscillograph plates 88, 89. Fig. 9 shows an obstacle detection apparatus comprising a transmitter 100, receiver 101, and a blocking device 102 for blocking the receiver during the transmission of impulses. Echo pulses are detected on a cathode-ray oscillograph 110, the sweep potential for which is provided by a saw-tooth generator 103 controlled by the transmission of impulses. When an echo pulse 106 appears on the screen of the oscillograph 110 the shape structure may be examined by using a saw-tooth wave produced by a generator 105 adjusted in delay by a delay unit 107 and passed through an amplitude gain control 108 and a double clipper 109 for use as sweep potential for a vernier oscillograph 115. The delay network 107 is adjusted to bring the inclined portion of the sweep potential wave into timed relation with the echo pulse 106, causing an expanded wave shape 106a with a base m, r to appear on the oscillograph 115. To expand the echo pulse further the gain control 108 is adjusted to increase the inclination of the saw-tooth wave. The resulting pulse shape 106b has a base o, p. The irregularity of the echo pulse shape depends upon the reflecting surfaces of the obstacle or obstacles and gives an indication of the nature of the obstacle, e.g. a squadron of air-planes would give a group of pulses as seen in the pulse shape 106b. Specifications 509,820, 511,222, 521,139, 523,575, 590,480 and 594,888 are referred to.