Patent GB-877436-A (GB)
Title: Improvements in or relating to electron beam-scanning systems
IPC: H04N3/34
Filed: 1958-08-18
Abstract: 877,436. Radar; cathode ray tube displays; valve pulse circuits; pulsing carrier frequencies. RAYTHEON CO. Aug. 18, 1958 [Aug. 26, 1957], No. 26483/58. Classes 40(5), 40(6) and 40(7) Apparatus for producing an interlaced spiral scan of an electron beam, comprises a scanning system which is triggered by a recurrent series of pulses, there being means for producing a series of spiral deflections, and means for delaying the initiation of each of the spiral deflections by differing delay times to produce said interlaced scan. In a radar system in which a storage device is between the main display and a remote radar indicator the information is written into, and read out of, the device between radar trigger pulses. Spiral scan is used during readout. According to the invention the scanning system uses two quadrature beam devices, there being means for producing a recurring series of equally spaced trigger pulses, each trigger pulse initiating a sine wave oscillation burst of predetermined duration, a generator for producing a recurring sequence of sawtooth waves, the initiation of each of the saw-tooth waves being delayed by differing amounts, means for modulating each of the sine wave oscillation bursts with the corresponding saw-tooth, and means for splitting the modulated wave into quadrature components which energize the deflection devices. A staircase generator 10 which generates eight steps comprises three bistable multi-vibrators which develop currents in resistors 25, 36, 41 such that the staircase voltage, Fig. 4g, appears at 26. The recurring series of trigger pulses, Fig. 4a, are fed to multi-vibrator 21. Each of the following multivibrators is triggered by the differentiated output of the preceding unit, Figs. 4c-4# By placing the staircase waveform and the trigger pulses on the anode of a phantastron valve 41, at the screen grid are obtained a recurring series of pulses, each pulse being of a duration proportional to the corresponding value of the staircase voltage, Fig. 4i. The recovery time of the phantastron is decreased by use of a cathode follower 42. A second phantastron 61 is fed with the differentiated pulses, Fig. 4j from the screen of valve 44. At the screen of this valve, therefore, there appears a recurrent series of pulses, of width controlled by potentiometer 54, the initiation of each pulse corresponding to the trailing edge of the pulses, Fig. 4i, from the first phantastron. These pulses trigger a bootstrap saw-tooth generator 14 via a cathode follower 13 In this circuit, a constant current passes in resistor 66 to charge capacitor 64. A sawtooth appears at the cathode of valve 68, Fig. 4l, and feeds to a paraphase amplifier 78. The saw-tooth waves, Fig. 4l, 4m, are used to modulate a sine wave oscillation burst. To obtain this burst the series of trigger pulses, Fig. 4a, triggers a phantastron 85. The square wave output obtained at the cathode gates an oscillator 16. The leading edge of this square wave initiates the oscillations in the tuned circuit 90 which feeds to the right hand section of valve 88. This section acts as a cathode follower, the cathode being returned to a tap on coil 91 to compensate for damping of the oscillations. The sine wave bursts pass via cathode follower 17 to be modulated in unit 18 by the saw-tooth waves. In any one series the sawtooth waves start at differing times after the start of the sine wave oscillation in order to produce interlace of the scan. The diode modulator unit 18 is of known form and feeds a tuned and paraphase amplifier to compensate for the clipping action of diodes 104, 105, and quadrature outputs which pass to deflection amplifiers appear at terminals 130, 131 of two RC phase-shifting networks.