Patent GB-1143485-A (GB)
Title: Improvements in or relating to the presentation of images
IPC: G01S7/00
Filed: 1966-04-19
Abstract: 1,143,485. Cathode-ray tube displays; P.P.I, displays. TELEFONAKTIEBOLAGET LM ERICSSON. 19 April, 1966 [20 April, 1965], No. 17187/66. Headings H4D and H4T. A P.P.I. display is controlled in accordance with signals indicative of range and of bearing by utilizing the range signals to produce deflection signals which, if the beam were present, would cause it to describe a circular path of radius dependent on the range and by pulsing the beam " on " by a pulse produced on coincidence of the bearing signals with an indexing signal corresponding to the instantaneous angular position determined by the deflection signals. The invention is concerned with producing a P.P.I. d splay at a location, remote from the radar set, to which range and bearing information is conveyed in binary code form over, e.g. ordinary telephone channels. Such information is fed to respective registers 11 range and 21 bearing (Fig. 1) either directly, if available in parallel form, or via a shift register 2 and gate 4 if in series form. The output of register-11 is converted to analog form in converter 8 in which it is employed to amplitude modulate a sinusoidal wave of frequency 250 c.p.s. derived via a band-pass filter 7 from the output of a ten stage binary counter 6 acting as a frequency divider for a 256 kc./s. pulse generator 5. The output of 8 comprising the sinosoidal wave amplitude modulated in accordance with range is then fed to the beam deflecting plates directly and via a 90 degrees phase shifter 9 to produce a circular deflecting field. A measure of the instantaneous angular position which the beam if present would occupy is given by the count in 6 and this is fed to a coincidence circuit 10 together with the bearing information output of register 21 and on agreement of the two inputs an output pulse on conductor 14 is utilized as a " bright-up " pulse for the tube beam, a pulse stretcher being included if required, e.g. when the number of targets per second which are to be presented increases and the frequency of 5, which must be increased, is so high that the coincidence time and therefore the duration of the " bright-up " pulse is reduced with a consequential reduction in brightness. However if the " bright-up " pulse is too long the target is presented in the form of a stroke, i.e. a part of a circle, and to avoid this the modification of Fig. 2 may be employed. In this arrangement the coincidence pulse from 10, Fig. 1, is utilized to amplitude sample the two sinusoidal waves in samplers 15, 16, the samples then being stretched in 17, 18 and supplied to the beam deflecting members whilst the coincidence pulse after delay in 22 and stretching in 23 is utilized as the " brightup " pulse. Instead of producing the 90 degrees phase shift on the modulated sinusoidal wave two digital-to-analogue convertors connected in parallel to register 11 and one of which is fed via the 90 degrees phase shifter 9 may be employed, Fig. 3, not shown. This is stated to have the advantage that the two deflection voltages occur simultaneously on the deflection plates instead of one, the cosine wave, occurring a quarter of a period later and thus incorrect presentation of the image is prevented should a different range value signal (due to another target or a different part of the first target) occur during this quarter period and result in the production of another sine wave with a different amplitude. In a further embodiment a rotating coil deflecting system supplied directly with the analog output of 8 is employed together with a code-disc rotating with the coil to supply the instantaneous angle information to the coincidence circuit (Fig. 4, not shown).