US3013263A - System for generating discrete side-byside displays on a cathode ray tube - Google Patents

Description

Dec. 12, 1961 w. ca. ALEXANDER EI'AL 3,

SYSTEM FOR GENERATING DISCRETE SIDE-BY-SIDE DISPLAYS ON A CATHODE RAY TUBE Original Filed June 26, 1950 6 Sheets-Sheet 1 INVENTORS WILLIAM G. ALEXANDER CHARLES M=L HARDEN ATTORNEYS w. G. ALEXANDER ET AL 3,013,263 SYSTEM FOR GENERATING DISCRETE SIDE-BY-SIDE Dec. 12, 1961 DISPLAYS ON A 'CATHODE RAY TUBE Original Filed June 26, 1950 6 Sheets-Sheet 2 522 6 i ov a:

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ATTORNEYS Dec. 12, 1961 w. G. ALEXANDER ETAL 3,013,263

SYSTEM FOR GENERATING DISCRETE SIDE-BY-SIDE DISPLAYS ON A CATHODE RAY TUBE Original Filed June 26, 1950 6 Sheets-Sheet 4 O A P On SPF-QM COPOUJMm nZZOKhONJN W INVENTORS WILLIAM G.ALEXANDER CHARLES M=L. HARDEN ATTORNEY Dec. 12, 1961 we. ALEXANDER EIAL 3,013,263

SYSTEM FOR GENERATING DISCRETE SIDE-BY-SIDE DISPLAYS ON A CATHODE RAY TUBE Original Filed June 26, 1950 6 Sheets-Sheet 5 WILLIAM G. ALEXANDER CHARLES M L. HARDEN Dec. 12, 1961 w. G. ALEXANDER ETAL SYSTEM FOR GENERATING DISCRETE SIDE-BY- ON A CATHODE RAY TUBE 3,013,263 SIDE DISPLAYS Original Filed June 26, 1950 6 Sheets-Sheet 6 h ad;

ATTORNE 5 Patented Dec. 12, 1961 3,613,263 SYSTEM FOR GENERATING DISCRETE SmEdBY- SIDE DISPLAYS ON A CATHODE RAY TUBE William G. Alexander, El Cajon, Calif., and Charles McL.

Harden, Natick, Mass, assignors to The Bendix Corporation, a corporation of Delaware (Iontinuation of application Ser. No. 170,326, June 26, 1950, now Patent No. 2,855,551, dated Gctoher 7, 1953. This application Dec. 5, 1957, Ser. No. 700,876

8 Claims. (Cl. 343-11) This invention is a continuation of application Serial No. 170,326, filed June 26, 1950, now US. Patent No. 2,855,591.

This invention relates to indicator systems and more particularly to a system for providing, on the face of a single cathode ray tube, a pair of simultaneous radar presentations each depicting the position of a common target with respect to reference indicia, when scanned in a respective plane.

The invention has particular reference to Ground Controlled Approach or GCA systems in which an aircraft is guided to a landing under conditions of poor visibility. In such systems as conventionally used, one or a pair of radio pulse echo systems (radars) scan a region of space including the desired glide path. Two antennas are used, one scanning through a horizontal plane and the other scanning through a vertical plane. The antennas are oriented to pick up the target aircraft and the pilot is directed by radio communication to correct his flight path to bring it into coincidence with the desired glide path.

It has been customary, in the past, to present the indication from each scan on a separate QR. tube, calling one the elevation presentation and the other the azimuth presentation. The fact that each presentation was on a separate tube made it necessary that a separate observer be supplied for each presentation. This added to the expense of operating the system.

The presentations, as normally used, are sectors of a plan position indication which have been distorted for more advantageous use. In their usual form they could not be combined on a single cathode ray tube face without overlapping unless they were reduced in size to an undesirable extent.

It is an object of this invention to provide a system by which a pair of radar presentations can be simultaneously shown on the screen of a single cathode ray tube.

It is another object of the invention to provide a system by which a pair of radar presentations of a combined size greater than that of the cathode my screen can simultaneously be shown on the said screen without a substantial reduction of size.

It is a further object of the invention to provide a system by which a pair of radar presentations may be combined on a single cathode ray screen in such positions that they would normally overlap, by eliminating the overlapping portions of the presentations.

It is a still further object of the invention to simultaneously display, on a single cathode ray tube screen, a pair of sectorial plan position indications of such size that they would normally overlap and to inhibit the generation of those portions which would normally overlap.

A further object of this invention is to provide a combined azimuth and elevation GCA system operating in pulse to pulse alternation between the azimuth and elevation radiations and a corresponding range sweep alternation of the data utilization device.

The objects and advantages of the invention are realized by a system in which each plan position indication is developed in alternation with the other. The alternation occurs at the end of each line of the scan. Portions of the two indications which would overlap are electronically inhibited by the use of gates which are varied in duration as the scan develops.

Referring now to the drawings:

FIG. 1 is a plan view of the screen of a cathode ray tube bearing a GCA elevation presentation;

FIG. 2 is a similar view of a screen carrying a GCA azimuth presentation;

FIG. 3 is a similar view of a screen carrying both the presentations of FIGS. .1 and 2, with portions in a region of overlap curtailed;

FIG. 4 is a schematic block diagram of a circuit embodying the invention;

FIG. 5 is a schematic block diagram of a portion of the circuit of FIG. 4;

FIG. 6 is a group of time related wave forms occurring in the circuit of FIG. 5;

FIG. 7 is a schematic diagram of the circuit of FIG. 5;

FIG. 8 is a schematic circuit diagram of an angle data selector circuit forming part of the circuit of FIG. 4; and,

FIG. 9 is a schematic circuit diagram of a circuit for clipping the azimuth and elevation presentations to prevent overlap, this circuit likewise being a part of the circuit of FIG. 4. i

Referring now more particularly to the drawing, FIG. 1 illustrates the circular screen 10 of a cathode ray tube on which is displayed a distorted sector of a plan position indication generated by the elevation scanning antenna of a GCA installation. Displayed on the surface of the screen, by some means other than the cathode ray'beam of the tube, is the outline of the pattern to which the indication generated by the tube is made to conform. This pattern may be permanently marked on the screen or may be projected on the screen from a source of visibleor invisible light or may be developed in any of a number of known ways. It consists of a generally triangular outline 11 conforming to the shape of a distorted sector of a plan position indication, having its point of origin 12 at the left hand side of the screen. A horizontal line 13 is also formed on the screen to represent the ground level to whichthe glide path is referred. The desired glide path is indicated by a'line 14 which joins the ground line 13. near the point or origin 12, the point of juncture representing the point of desired touch down of an aircraft on the runway. Formed parallel to the glide path line 14 are a pair of dotted lines 15 which represent reference distances from the glide path by which the error in elevation of a plane being guided can be visually determined. Such lines could, for example, indicate distances of 50 feet above and below the glide path. Shown also in this figure are spaced vertical lincs16 which are range marks having a spacing, for example, of One mile by which the distances of the plane from the point of touch down can be seen at a glance. These range marks may be marked on the screen or may be generated electronically by the cathode ray tube.

There is shown in FIG. 2 an indication 17 of the screen of a second cathode ray tube bearing an indication of a second distorted sector of a plan position indication representative of the scan of the azimuth scanning antenna of the GCA system. The sector has its origin at the point 18 located at the top of the screen and has a triangular outline-19, having a horizontal base at the bottom of this screen. Erected on the base is a vertical line 20 representative of a plan view of the desired glide path as seen by a pilot of an approaching aircraft. A small rectangular representation 21 of the runway is formed at the top of the line 20. A pair of dotted lines 22 equally spaced on opposite sides of the line 29 provide reference indications of azimuthal discrepancies between the position of the planeand the glide path. These lines can, for example, indicate distances of 50 feet on either side of the glide path.

Horizontally extending range marks 23 are also formed on this indication, either electronically by means of the cathode ray means or by the same means as the remainder of the indication.

On each of the displays of FIGS. 1 and 2 the location of the aircraft is indicated by a luminous dot generated electronically by the cathode ray beam of the tube in response to the video signal of the radar set or sets used in the system.

GCA systems as known to the art may employ either one or two radar sets in connection with the scanning antennas. If one radar set is used, the set is connected alternatively to each of the two antennas. The alternation may occur at the end of each scan or at the end f each line of the scan. If two radar sets are employed each set may be continuously connected to a respective one of the two antennas. In order to eliminate cross talk when the latter type of system is used, the antennas may be pulsed in alternation only one radar set being activated at a time.

The present invention is concerned with a means by which the two displays of FIGS. 1 and 2 may be combined on a single tube for observation by a single observer Without overlapping of the displays and without reduction of their size to a point at which their legibility is impaired. The invention is useable for GCA systems employing either one or two radar sets and in which the antennas are activated sequentially at the termination at the end of each line. A combined display in accordance with the invention is illustrated in FIG. 3. The screen of the tube is indicated at 26. The elevation display similar to that of FIG. 1 appears in the upper half of the screen, while the azimuth display similar to that of FIG. 2, but reoriented so that the glide path now lies in a horizontal direction, is formed on the lower half of the tube. The outlines 11 and 19 may be patterns formed by means other than the cathode ray beam of the tube to which the indications generated by the cathode ray tube are caused to conform just as in the displays of FIGS. 1 and 2. It will be noted that the lower portion of the elevation display beneath the horizontal ground line 13 has been removed except for a small portion 11 at the left hand edge of the display. It will also be noted that the upper portion of the azimuth display has been removed, the display now terminating in its upper portion in a horizontal line 27 which runs parallel to the ground line 13 of the elevation display.

With respect to all three figures, it will be understood that the indication generated by the cathode ray beam of the tube is that of the usual sectorial plan position indication distorted in a manner known to the art to provide a more realistic indication to the observer. Thus, in each indication the cathode ray beam at the beginning of each scan line starts at the point of origin of the display such as point 12 in FIG. 1 and point 18 in FIG. 2 and proceeds radially from that point for a predetermined length of time and then flies back to that point and begins the generation of a second radially line displaced from the first by a small angular amount. This action continues until the entire triangular indication has been generated whereupon the generation of the indication is repeated. If during the generation of the indication an aircraft is encountered by the radiated beam, the cathode ray beam of the tube is intensified to produce a spot of light on the indication representative of the position of the aircraft at that instant.

The same manner of generation is followed in FIG. 3, the two indications being generated by alternate excursions of the cathode ray beam. This alternation occurs at the end of each line of each scan. The alternation occurs so frequently that by' reason of the presistence of vision of the human eye, the two scans do not appear in alternation, but rather appear as a constant unflickering presentation as though both were simulaneously and continuously present on the tube screen.

There is shown in FIG. 4 a block diagram of an entire GCA system embodying the invention. The system includes an azimuth scanning antenna 3%, the radiated beam of which has a cross sectional configuration as shown at 31 and scans in a horizontal path indicated by the line 32. Connected to this antenna, in the usual manner, for transmission and reception, is a radar transmitter and receiver 33 having a video output terminal indicated at Z.

An elevation antenna is indicated at 34, the radiated beam of which has a cross sectional configuration as indicated at 35 and scans in a vertical path indicated by the line 36. To this antenna is connected, in the usual manner for transmission and reception, a radio transmitter and receiver 37. The receiver of this set is provided with a video output terminal indicated at Y.

Both the scan paths 32. and 36 include the glide path down which incoming aircraft are to be guided to a landmg.

A cathode ray tube 38 having a screen 26 is provided upon which the display of FIG. 3 is to be presented. The cathode ray tube is provided with horizontal deflection coils 39, 40 and vertical deflection coils 41, 42 which operate in the usual manner. The tube is also provided with a cathode 43 and a pair of control grids 44 and 45. A horizontal driver circuit 45 is provided which generates a current output having a saw-tooth waveform for deflecting the beam of the tube across the screen in a horizontal direction in a known manner. A clamp circuit 24 insures that the hon'zontal deflection voltage return to the same starting value after each sweep. The vertical driver circuit 47 performs the same function as circuit 46 with respect to vertical deflections of the cathode ray V. A clamp and cathode follower circuit 62 performs functions similar to circuit 24, as well as other functions which will be described later. An intensifier circuit 49 is provided which intensifies the cathode ray tube beam during each radial sweep to the point of producing a visible trace on the screen.

An azimuth video amplifier circuit 50 receives the video output of the radar set 33 by way of terminal Z and applies it to a video mixer 51. Here it is mixed with range marks generated in a manner to be later described and the output of the mixer is amplified in the video output circuit 52 and applied to the control grid 44 of the cathode ray tube.

An elevation video amplifier 53 receives the video output of radar set 37 by way of terminal Y and after amplification applies it to the video mixer 51. The outputs of the amplifiers 50 and 53 are applied to the video mixer at diiferent times as will be explained hereafter.

A range mark generating system is also supplied. This includes a range mark delay circuit 51 triggered by pulses from gate generator 60 by means of which the point of origin, from which the range marks are generated, can be adjusted manually as desired. This circuit provides a variable delay means which operates in a known manner to perform this function. The output of the circuit controls the phase of range mark oscillations produced in a range mark oscillator and shaper circuit 52. This circuit contains an oscillator producing an output having a frequency selected to result in the generation of range marks separated by desired intervals, the usual interval being a mile. The output of this oscillator is clipped into a square wave form and utilized to synchronize a range mark blocking oscillator 53. A range mark starting circuit 54 is provided which initiates the action of the blocking oscillator 53. The output of the range mark blocking oscillator 53 is applied to the video mixer 51 with the result that the output of this mixer consists of video signals received from the radar set 33 or 37 combined with range marks.

The portion of the circuit of FIG. 4 which has been described above is of a conventional nature. The remainder of the circuit of this figure has been added in accordance with the invention in order to provide for the simultaneous display of azimuth and elevation information on the screen 26. In order to accomplish this result, it is necessary that the azimuth and elevation displays be generated in alternation. In order to generate such displays in alternation, switching arrangements must be provided so that, for example, when the elevation display is being applied to the screen, each line of the scan will start from the point of origin which has been selected for that display and which is different from the point of origin selected for the azimuth display. There likewise must be utilized video information coming from the radar set 37 and angle data voltage related to the position of the elevation antenna 34.

There are two possible methods of generating side-byside displays, in the first of which the displays are generated in alternation after each scan line, thus one line of the scan of the elevation antenna will be generated and then a line of the scan of the azimuth indication will be generated. The other alternative is to generate the entire elevation scan and then generate the entire azimuth scan. The present invention is directed to systems in which the alternation occurs after each line of the scan.

Thus, following the generation of one line of the elevation scan utilizing the elevation video information and angle data voltage, it is necessary that the system now be switched to receive only data from the radar set 33 and the azimuth antenna 3th. This switching between azimuth and elevation data must occur at the pulse repetition frequency utilized by the radar sets. For purposes of illustration, we may assume that this frequency is 2400 cycles per second.

The system as shown in FIG. 4 includes an electronic selector switch 55 which performs several of the switching functions referred to above. This switch is triggered by a system trigger generated elsewhere in the system and recurring 2400 times per second. The switch generates triggers which are applied by conductors 56 and 57 to the transmitter of the azimuth radar set 33 and the transmitter of the elevation radar set 37 respectively. These triggers are separated by time intervals of approximately 215 micro-seconds. These triggers are also supplied by conductors 58 and 59 to a gate generator of which generates a series of square gating pulses that are applied to various parts of the circuit in a manner to be described later.

The selector switch 55 also performs the function of alternately switching the video input to the cathode ray tube from that supplied by radar set 33 to that supplied by radar set 37 and back again. In order to perform this function the selector switch generates gates which occur in alternation and each of which is supplied to a respective one of the video amplifiers 50 and 53 so that these amplifiers are gated into a conductive state in alternation.

In connection with the azimuth and elevation scanning antennas there are produced a pair of voltages which vary as a function of the instantaneous scanning position of the respective energy beams emitted from these antennas. These antennas may each comprise a linear array of dipoles mounted on a variable width wave guide as described in volume 26, entitled Radar Scanners and Radomes of the Radiation Laboratory Series, published 1948 by McGraw-Hill Book Company, Inc., New York City. The description will be found on pages 185-193 inclusive. The width of these antennas is cyclically and synchronously varied to produce the scanning of their beams. This width varying means may, by a simple mechanical linkage, be caused to vary the setting of a pair of potentiometers to produce the pair of voltages referred to. These voltages are used to modify the vertical deflection current applied to the coils 41 and 42 in order that distortion of the display may be secured in order to produce the presentations in the manner illustrated. These voltages are also employed to clip the presentations through the use of gating voltages in order that the two displays may be applied to the same cathode ray screen in the manner illustrated in FIG. 3. In order to carry out these functions the electronic selector switch 55 produces a pair of gating voltages which are applied to an angle data selector 61, the output of which is applied to the clamp and cathode follower circuit 62. The angle data selector receives input voltage from the antennas 3t and 34 by way of conductors 63 and 64. The gates developed by the switch 55 determine which of these input voltages is to be utilized at a given time since they also are employed in alternation. A map clipper 65 is employed to generate the necessary gating voltages for clipping the azimuth and elevation displays as illustrated in FIG. 3. This circuit receivers an input from the angle data selector 61 of the angle data passed by that circuit and also receives gating voltages from selector switch 55.

In order to establish the respective points of origin of the azimuth and elevation displays, a pair of centering circuits are employed, each establishing one component of the points of origin of these displays. The centering circuit related to the horizontal deflection system comprises a triode 66, the anode of which is connected by way of a resistor 67 to the coil 39 of the horizontal deflection system. The control electrode of this tube receives gating voltage from the selector switch 55 by way of a conductor 63. The centering system relating to the vertical deflection system comprises a triode 70, the anode of which is connected by way of a resistor 71 to the coil 41 of the veitical deflection system. The control electrode of this tube receives gating voltage from the selector switch 55 by way of a conductor 72.

The make-up and functioning of the electronic selector switch 55 is more fully set forth in FIGS. 5, 6 and 7. FIG. 5 is a block diagram of the switch, while FIG. 6 illustrates the waveforms at different points of the circuit of FIG. 5. The waveforms are identified by block letters in FIG. 6 and the points where they are found in FIG. 5 are likewise indicated by the use of the same letters. The basic element of the switch is a multivibrator circuit 73, having a 50% duty-cycle, the complete cycle occupying a time of approximately 430 microseconds. The system trigger is applied to the input of this circuit from the terminal X. This trigger has a waveform such as shown at A in FIG. 6. It can be seen that this waveform comprises a series of positive impulses separated by time intervals of 430 micro-seconds. The output of the multivibrator 73 is taken at two points, differentiated and applied as the waveforms B and C to the inputs of two isolation amplifiers 74 and 75. Wave forms B and C are seen to be the clifierentiated products of the output of a multivibrator having a 50% duty-cycle. Each waveform consists of a series of impulses of alternate polarity, impulses of positive polarity being produced at the leading edge of the positive portion of the multivibrator waveform and impulses of negative polarity being produced at the leading edges of the negative portions of the multivibrator waveform. The impulses of the two waveforms are reversed in polarity. The isolation amplifiers 74 and 75 eliminate the negative-going impulses and amplify the positive-going impulses of these waveforms to produce output waveforms D and E. These two waveforms are applied as triggering voltages to the transmitters of radar sets 33 and 37 and to the gate generator 6t) as described above in connection with FIG. 4. These waveforms are also utilized as triggering voltages in two micro-second multivibrators 76 and '77. The outputs of these multivibrators are the waveforms F and G which are seen tov be square pulses of 80 microseconds duration, separated by time intervals of 430 micro-seconds. The pulses of each of these waveforms occur midway of the pulse intervals of the other.

One of the two multivibrators 76 and 77 may be identically duplicated in the gate generator 6%, since the output of that generator is a waveform identical with the sum of F and G. If desired, the multivibrators 76 and 77 may be utilized as the gate generator 60 with appropriate output leads to the various elements of FIG. 4 which are shown as receiving the 80 micro-second pulse output of generator 60. For clarity, however, a separate gate generator 60 has been illustrated in FIG. 4. The outputs of the multivibrators 76 and 77 are applied to respective isolation amplifiers 78 and 79. The output of these amplifiers is applied to the map clipper :ircuit 65 which will be later described.

The output waveform F from multivibrator 76 is also differentiated to produce the waveform H which is applied to the input of a 215 micro-second multivibrator 86 From this circuit two waveforms J and K are recovered, these being taken from points of opposing polarity in the output circuit of the multivibrator. As will be seen, these waveforms consist of square waves having alternating, positive and negative-going portions of 215 micro-seconds duration. The positive portions of these waveforms are utilized as gates for various parts of the circuit of FIG. 4. It will be noted that these positive portions occur in the two waveforms in alternation. They are amplified in gate amplifiers 81 and 82 before use. The waveforms J and K are applied to the angle data selector 61 in which circuit they are utilized in a manner to be later described. The waveform I is also applied to the control electrodes of centering tubes 66 and 76 which have been previously described. The application of this waveform to these tubes causes the conduction thereof to be shifted between two different levels, one level occurring during the application of data relating to the elevation presentation to the cathode ray tube and the other level occurring during the presentation of data relating to the azimuth presentation.

Turning now to FIG. 7, we find that the multivibrator 73 comprises the two tubes 85 and 86 and their associated circuit elements. The waveform A is applied from terminal X to the control electrode of tube 85 which is normally in a non-conducting state. The positive impulses of this waveform trigger the multivibrator by causing the tube 85 to conduct. Once this action has been started, the waveform A synchronizes the action of the multivibrator to its recurrence. The waveform B consists of the impulses of waveform A, plus negative-going impulses derived from the control grid of tube 85. When this tube ceases to conduct at the change-over point of the multivibrator action, the negative-going impulses are derived by differentiation of the control electrode voltage in the network composed of condenser 87 and resistor 88. This waveform is applied to the control electrode of a tube 89 which is a part of isolation amplifier 74. The waveform C is derived from the anode of tube 85 by differentiation of the leading edges of the excursions of the multivibrator output. This differentiation occurs through a network composed of condenser 90 and resistor 91 and the resulting waveform is applied to the control electrode of a tube 92 which, with its circuit elements, comprises isolation amplifier 75.

The waveforms D and E are derived from the cathodes of tubes 89 and 92 respectively, from whence they are applied to the transmitters of radar sets 33 and 37 and to the input circuits of multivibrators 76 and 77. Multivibrator 76 is composed of tubes 93 and 94 and their associated circuit elements and multivibrator 77 is composed of tubes 95 and 96 and their associated elements. The waveform D is applied to the control electrode of tube 93 and the Waveform E is applied to the control electrode of tube 95.

The waveform F is derived from the anode circuit of tube 94 of multivibrator 76 and the waveform G is derived from the anode circuit of the tube 95 of the multivibrator 77. The waveform F is applied to the control electrode of tube 97 which, with its circuit elements, constitutes the isolation amplifier 78 and the waveform G is applied to the control electrode of the tube 98 which is a part of the isolation amplifier 79. Outputs from the cathodes of these tubes are available as gating voltages and are utilized for this purpose in the map clipper circuit 65.

The waveform H is derived from a variable tapping point on a resistor 99 in the anode circuit of tube 93. The voltage from this point is differentiated through a network consisting of condenser 16% and resistor 101, and is applied to the control electrode of a tube 102 which, with a tube 183 and their associated circuit elements, comprises multivibrator 81 From the anode circuit of tube 102 is derived the waveform K, while the waveform J is taken from the anode circuit of tube 103. These Waveforms are applied to the respective control electrodes of two tubes 184- and 105 which respectively, with their associated circuit elements, constitute gate amplifiers 81 and 82. From the cathode circuits of these tubes the Waveforms J md K are available and are supplied to the necessary elements of the circuit of FIG. 4.

The schematic circuit diagram of the angle data selector 61 is illustrated in FIG. 8. In that figure we find a pair of terminals M6 and 107 across which azimuth angle voltage from the azimuth scanning antenna 39 is applied to the anodes of a pair of clamping tubes 108 and 109 through a pair of resistor 110 and 111. Voltage of the waveform K is applied from terminal 112 to the control electrodes of these tubes. Across a second pair of terminals 113 and 114 elevation angle voltage from elevation scanning antenna '34 is applied through resistors 115 and 116 respectively, to the anodes of two clamp tubes 117 and 118. Voltage of the waveform J is applied to the control eelctrodes of these tubes from terminal 119. The control grids of tubes 117 and 118 are connected through a resistance network to a source of negative voltage represented by terminal 120. This source establishes a bias on these grids, of sulficient magnitude to render the tubes non-conductive in the absence of a positive voltage applied to the control grids. On the other hand, the tubes 108 and 169 are conducting in the absence of a negative voltage applied to their control grids.

A pair of tubes 121 and 122 have their cathodes directly connected and connected through a resistance network to the terminal 121}. The control electrode of tube 121 is connected to the anode of tube 108 across resistor 110 and the control electrode of tube 122 is connected in the same manner to the anode of tube 117 across resistor 116. An output terminal 123 is dierctly connected to the cathodes of these tubes.

A pair of tubes 124 and 125 have their cathodes directly connected and connected through a resistive network to the terminal 128. The control electrode of tube 124 is connected to the junction between the anode of tube 109 and resistor 111 and the control electrode of tube 125 is connected to the junction of the anode of tube 118 and resistor 115. A terminal 126 is directly connected to the cathodes of these tubes.

In the operation of this circuit the tube 108 is normally heavily conducting. The application of the negativegoing excursion of the waveform K to its control grid is suflicient, however, to cut-oif conduction therein. So long as tubes 1118 and 1119 are conducting, their anode voltage, applied to the control grids of tubes 121 and 124, is suificient to render these tubes non-conducting so that the application of azimuth angle voltage to the terminals 166 and 197 is ineffective to produce an output at the terminals 123 and 126. Due to the reversed polarity of the waveforms I and K at the times when tubes 108 and 109 are conducting and no azimuth angle voltage may, therefore, be derived from terminals 123 and 126, a negative-going excursion of the waveform I is being applied to the control electrodes of tubes 117 and 118. This, in conjunction with the application of biasing voltage from the terminal 120, maintains these tubes in a non-conductive state so that elevation angle voltage be ing applied across terminals 113 and 114 is effectively 9 applied to the control electrodes of tubes 122 and 125 causing those tubes to conduct. Since the terminals 123 and 126 are directly connected to the cathodes of tubes 122 and 125 elevation angle voltage is available across terminals 123 and 126.

Now as soon as a negative-going excursion of the'waveform K is applied to the control grids of tubes 16S and M9, conduction in these tubes is caused to cease, with the result that the tubes 121 and 124 are now rendered conductive and azimuth angle voltage is therefore applied across the terminals 123 and 126. At the same time a positive-going excursion of the waveform J is being applied to the control electrodes of tubes 117 and 118, with the result that these tubes are now rendered conductive and by their conduction render tubes 122 and 125 non-conductive. During this period of time, therefore, no elevation angle voltage is applied across terminals 123 and 126.

it can thus be seen that elevation angle voltage and azimuth angle voltage are alternately available from the output of this circuit during successive periods of 215 micro-seconds each.

FIG. 9 shows a schematic diagram of the map clipper 65 and of the clamp and cathode follower circuit 62 and the vertical driver circuit 47. The clamp and cathode follower circuit comprises a cathode follower circuit utilizing a tube 127, the output of which is taken from its cathode and supplied through a potentiometer 123 tothe control electrode of tube 131), forming a part of the vertical driver circuit. Angle data voltage from the angle data selector 61 is supplied to the control electrode of tube 127 by way of a terminal 129. A clamp tube 155 has its anode connected to the control grid of the tube 136' and receives pulses from the gate generator oil by way of terminal 156.

The tube 13a is connected for operation as a relaxation oscillator with an output which has a saw-tooth waveform. To this end the anode is connected to B+ through an inductance 157 and a feedback path from the anode to the control grid is provided by way of a resistor 158 and condenser 159. The output voltage of this circuit is the vertical deflection voltage applied to the vertical deflection coils 41 and 42 of the cathode ray tube. It is also utilized in the map clipping circuit in a Way to be described.

The tube 130 can only be rendered conductive during the receipt of a gating impulse from the gate generator 60 by way of clamp tube 155 and the time constants of the circuit 47 are such that each saw-tooth of its output occupies the whole duration of the gating impulse, the control grid of the tube 130 being returned by the clamp tube 155 to a fixed reference voltage at the end of. each gating impulse. The angle data voltage applied by the cathode follower 127 governs the amplitude of the output saw-tooth of circuit 47.

The output of the circuit 47 is shown as a negativegoing saw-tooth excursion 131 which is applied by way of a condenser 132 to a resistor 133. This resistor is connected as a potentiometer to the control grid of amplifier tube 134. The waveform of the voltage applied to this grid by way of the potentiometer is indicated at 135. The cathode of this tube is connected by way of a potentiometer 136 to a source of negative voltageindicated by the terminal 137. This tube will conduct during the: initial portion of the Waveform 135 depending upon the setting of the potentiometer 133. The final portion of the waveform 13$ will, however, cause thetube to be cut-off with the result that an output waveform, as indicated at 138, will be produced. This output will have the form of a substantially square topped, positive-going pulse. The duration of this pulse is seen to be dependent upon the amplitude of the negative-going saw-tooth 131 which is governed by the angle data voltage. The terminal edge of the pulse 138 is fixed, so that an increase ins the amplitude of the waveform 131 will result in'the lead The pulse is differentiated in the network comprising a condenser 139 and a resistor 141 to produce a resulting waveform of the type shown at 141 which is applied to the control grid of a pentode coincidence tube 14-2. This tube is normally in a non-conducting state due to the application of a negative voltage from a source indicated by a terminal 143 through the resistor w the control grid. The suppressor grid of tube 142 is connected by a resistor 144 to ground. Negative voltage is supplied by way of a terminal 145 through a resistor 146 to the junction of resistor 144 and th e suppressor grid. Likewise applied at this point is the waveform G which is applied from the selector switch 55 by way of a terminal 147 through a resistor 148. The tube 142 is normally biased so heavily that it requires the coincidental application of the positive-going spike of the waveform 141, and a positive-going excursion of the waveform G to render it momentarily conducting. When this occurs a negativegoing spike, as indicated at 149, will be applied to the input circuit of a one shot multivibrator 150. This multivibrator comprises a pair of tubes 151 and 152. The control grid of tube 151 is connected to B+ through a resistor 153 of such value that this tube is normally conducting and tube 152 is normally non-conducting. The application of the negative-going spike 149 to the control grid of tube 151 triggers the multivibrator through one cycle of its operation, whereupon it returns to its initial condition and remains in that state until the receipt of another negative triggering spike. Output from the multivibrator 151) is taken from the anode of tube 152 at terminal 154 and is applied by way of conductor 48 to the electrode 45 of the cathode ray tube 38, as shown in FIG. 4. It can be seen that this voltage, in the normal state of the multivibrator 150, will be a positive voltage. Upon the application of the negative trigger 149, the multivibrator will generate a negative-going voltage ex cursion which will have a duration dependent upon the time constants of the multivibrator circuit.

The portion of the map clipping circuit which has been described is that which performs the function of clipping the azimuth presentation which is the lower presentation of FIG. 3. It can be seen from that figure that it is necessary to clip the upper portion of the presentation along a horizontal line. This is accomplished through the effect of the angle data voltage, the gate impulses from gate generator 60, and the waveform G upon the circuit described above. The application of waveform G to the suppressor grid of tube 142 insures that that tube can conduct only during those times when angle data voltage from the azimuth antenna is available from the angle data selector 61. The angle data voltage applied by way of terminal 129 and tube 127 regulates the amplitude of the saw-tooth waveform 131 in the manner described, so that the amplitude of that waveform is a function of the instantaneous scanning position of the energy beam from the aximuth an-. tenna, with the amplitude of the waveform increasing as the antenna scans from left to right as Viewed by an incoming pilot. Until the scan position has moved to a point several degrees to the right of the horizontal base line of the azimuth scan, the amplitude of the waveform 131 is too small to cause the production of a pulse 138 in the output of the tube 134 and thus, the multivibrator is not triggered and no clipping occurs. As the scan position reaches this point, however, the amplitude of the waveform- 131 has increased to an amount suflicient to begin with a production of pulses 138 in the output of tube 134. Thus the circuit begins to clip the upper portion of the presentation near the right hand edge of the cathode ray screen. As the beam swings further to the right, the amplitude of the waveform 131 increases and the leading edge of the pulse 138 occurs progressively earlier in time with the result that clipping now occurs sooner in the duration of each radial trace of the beam of the cathode ray tube. With the proper control of the variation of the amplitude of the waveform 131, as the antenna beam swings to the right, the line 27 marking the upper boundary of the azimuth scan may be made to be horizontal.

We come now to the portion of the map clipper which eiiects the clipping of the elevation presentation or the upper presentation of FIG. 3. This portion of the circuit includes a multivibrator 160 of the one shot type which, on being triggered, generates a positive pulse 161 of approximately micro-seconds duration and then reverts to its quiescent state until it is again triggered. This multivibrator comprises a pair of tubes 162 and 163. System triggering voltage of negative polarity resembling the waveform A is applied to the control grid of tube 162 by way of terminal 164. Elevation gating voltage of the waveform F is applied to the anodes of the multivibrator tubes through resistors 165 and 166 respectively, by way of terminal 167. An amplifier 168 is provided having its anode connected to the anode of tube 162 and its cathode connected to ground by way of a variable tap on a resistor 169. Positive voltage from a source 3-! is applied to the cathode by way of terminal 170 and resistor 171. Elevation angle data voltage is applied to the control grid of tube 168 by way of the terminal 172. The anode of tube 162 is connected to a source of negative voltage through a condenser 173 and a resistor 174 by way ofa terminal 175. r

The multivibrator 160 is not operative in the absence of a positive gating voltage of waveform F. When this voltage is applied to the anodes of the multivibrator tubes, the multivibrator is in its quiescent state. The application of the negative system trigger voltage to the control grid of tube 162 would result in the triggering of the multivibrator if it were not for the presence of the tube 163. When the elevation antenna beam is in the above ground portion of its scan the elevation angle data voltage applied to the grid of tube 168 causes that tube to conduct sufficiently to maintain the anode voltage of tube 162 at a value such that the negative system trigger applied to its control grid cannot be amplified and the multivibrator fails to respond to that stimulus. When, however, the elevation antenna scan moves to a position below the ground level the elevation angle data voltage is reduced until the tube 168 nears the point of out-01f. 'In this condition the anode voltage on the tube 162 is high enough in the presence of the waveform F to respond to the system trigger and to generate its output pulse 161. This is applied through a variable tap on resistor 165 and by way of a condenser 176 to the control grid of tube 151 of multivibrator 156. The trailing edge of this pulse triggers the multivibrator 150 into its unbalanced state. It can thus be seen that during the duration of the positive-going excursions of the waveform F, the multivibrator 160 is activated but unable to respond to the system trigger until the scan position of the elevation antenna moves below ground. At this time the multivibrator responds to the system trigger to generate the pulse 161. This pulse is of sufiicient duration to allow the generation of the portion 11 of the elevation presentation shown in the upper part of FIG. 3. The trailing edge of this pulse initiates the output pulse of the multivibrator 150 which blanks the cathode ray tube for the duration of the sweep of each sweep of the cathode ray beam following the termination of the pulse 161,

To summarize the operation of the entire system depicted in FIG. 4, we have a pair of antennas scanning a common region containing a glide path down which aircraft are to be guided to a landing. The azimuth antenna 36 base directive beam 31 scanning along the 12 horizontal path 32. The elevation scanning 34 has a directive beam 35 scanning vertically along a path 36. The azimuth and elevation antennas are connected respectively, to two radar sets 33 and 37.

An electronic selector switch 55 is provided which responds to a system trigger, consisting of an impulse generated at regular intervals of 430 micro-seconds, to generate various output impulses. It generates two triggering voltages of the waveforms D and E corresponding in form to the Waveform of the system trigger A, but with the impulses of one waveform occurring midway of the intervals between the impulses of the other. These impulses are utilized to trigger the two radar sets alternately into activity, a single radar pulse being transmitted upon the receipt of each trigger. The same triggering voltages are also applied to a gate generator 60 which generates an micro-second positive-going impulse upon the receipt of each trigger. These 80 micro-second impulses are utilized in several portions of the circuit. They activate a range mark generating circuit. They also activate horizontal and vertical drivers which generate deflection voltages for the deflection circuits of a cathode ray tube 38. They are also applied to an intensifier circuit which causes the generation in the cathode ray tube of a beam of sufficient intensity to produce a visible trace on the tube screen for the duration of the impulse.

The video output of the radar receivers of sets 33 and 37 are applied respectively to azimuth and elevation video amplifiers 5t) and 53. These amplifiers are also activated in alternation by 215 micro-second impulses generated by the selector switch 55. This alternate activation renders each amplifier active at a time when its respective radar set is transmitting a pulse and receiving video information from any targets which may be present. The output of these amplifiers is mixed with the range marks generated by the range mark generating circiut and applied to the cathode ray tube. The waveform J is also applied to the control grids of two centering tubes 66 and 70 which operate on the two deflection circuits and, by virtue of the alternating levels of the waveform 1, cause the two displays on the tube screen to be generated at different locations on the screen.

Angle data voltage is also generated by each of the antennas 3t) and 34 and used to control the clipping of the two presentations in order that they may be displayed on the screen in as large a size as possible without overlapping at their adjacent edges. To perform this function an angle data selector 61 and a map clipper circuit 65 are provided. The angle data selector is controlled by the two waveforms J and K and thereby caused to alternately present in its output angle data voltage from each of the two antennas. This alternation is in synchronisrn with the activation of the two video amplifiers and the two centering tubes 66 and 70, in order that everything pertaining to each respective presentation be segregated into respective alternating time intervals. The map clipper 65 receives voltages of the two waveforms F and G and the elevation trigger voltage of waveform D from the selector switch 55. It also receives angle data voltage from the angle data selector 61 and has applied to it the output of the vertical driver 47. From these inputs it generates gating voltages appropriate to each presentation during the time intervals when that presentation is being generated and clips each respective presentation along the portion of its boundary which is adjacent to the other presentation and would otherwise overlap.

It should be understood that the values of voltages and times that have been given herein are for the purpose of illustration only and are not to be considered as restrictive of the invention.

What is claimed is:

1. A radio pulse echo system comprising radio transmitting and receiving means, a pair of directive antennas, each scanning a respective sector of space, a cathode ray tube, means generating a pair of voltages each varying in accordance with the scan of a respective one of said antennas, means impressing on each antenna in alternation a pulse of radio frequency energy, and means generating on said cathode ray tube a discrete plan position indication of the output of said system as derived from each of said antennas, said indication generating means comprising means repetitively generating a saw-tooth output voltage in synchronism with the emission of said pulses, means responsive to said output voltage for repetitively deflecting the ray of said cathode ray tube in synchronism therewith, switching means applying said pair of voltages to said saw-tooth voltage generator in alternation in synchronism with said pulses to vary the amplitude of said output voltage in accordance therewith, means generating a biasing voltage alternating between two values in synchronism with said pulses .and means applying said biasing voltage to said deflecting means to alternate the starting point of said deflections of said cathode ray beam between two locations.

2. A radio pulse echo system comprising radio transmitting and receiving means, a pair of directive antennas, each scanning a respective sector of space, a cathode ray tube, means generating a pair of voltages each varying in accordance with the scan of a respective one of said antennas, means impressing on each antenna in alternation a pulse of radio frequency energy, and means'generating on said cathode ray tube a discrete plan position indication of the output of said system as derived from each of said antennas, said indication generating means comprising means repetitively generating a saw-tooth output voltage in synchronism with the emission of said pulses, means responsive to said output voltage for repetitively deflecting the ray of said cathode ray tube in synchronism therewith, switching means applying said pair of voltages to said saw-tooth voltage generator in alternation in synchronism with said pulses to vary the amplitude of said output voltage in accordance therewith, means generating a biasing voltage alternating between two values in synchronism with said pulses and means applying said biasing voltage to said deflecting means to alternate the starting point of said deflections of said cathode ray beam between two locations, said switching means comprising: a first pair of electron discharge tubes each having an anode, a cathode and a control electrode, said tubes having their cathodes directly connected and connected to one side of said translation channel, a second pair of electron discharge tubes each having an anode, a cathode and a control electrode, said tubes having their cathodes directly connected together and to the remaining side of said translation channel, a first pair of clamping devices, each having an input and an output circuit, means can necting the output circuit of each of said clamping devices to the control electrode of a tube of a respective one of said pairs of tubes, a second pair of clamping devices, each having an input and an output circuit, means connecting the output circuit of each of said clamping devices to the control electrode of the remaining tube of a respective one of said pairs of tubes, means rendering said pairs of clamping devices conductive and non-conductive in alternating periods of equal duration synchronized with said pulses, the devices of each pair being conductive when those of the other pairs are non-conductive and means coupling a respective voltage of said pair of voltages across the output circuits of each pair of said clamping devices. a

3. A radio pulse echo system comprising radio transmitting and receiving means, a pair of directive antennas, each scanning a respective sector of space, a cathode ray tube, means generating a pair of voltages each varying in accordance with the scan of a respective one of said antennas, means impressing on each antenna in alternation a pulse of radio frequency energy, and means generating on said cathode ray tube a discrete plan position indication of the output of said system as derived from each 14 of said antennas, said indication generatingmeans comprising means repetitively generating a saw-tooth output voltage in synchronism with the emission of said pulses, means responsive to said output voltage for repetitively deflecting the ray of said cathode ray tube in synchronism therewith, switching means applying said pair of voltages to said saw-tooth voltage generator in alternation in synchronism with said pulses to vary the amplitude of said output voltage in accordance therewith, means generating a biasing voltage alternating between two values in synchronism with said pulses and means applying said biasing voltage to said deflecting means to alternate the starting point of said deflections of said cathode ray beam between two locations, said switching means comprising: means generating a pair of squarewave voltage outputs with the positive-going excursions of each of said outputs coinciding in time with the negative-going excursions of the other, a first pair of electron discharge tubes each having an anode, a cathode and a control grid, the cathodes of said tubes being directly connected, means connee ting said cathodes to one side of saidtranslation channel, a second pair of electron discharge tubes each having an anode, a cathode,'and a control electrode, the cathodes of said tubes being directly connected, means connecting said cathodes to the other side of said translation channel, a first pair of clamping devices each having an input and an output circuit and being so connected as to be normally conductive, means impressing on said input circuits one of said squarewaves outputs, means connecting the output circuit of each of said devicesto the control electrode of'a tube of a respective one of said pairs of tubes, means coupling one of said pair of varying voltages across the output circuits of said first pair of clamping devices, a second pair of clamping devices each having an input and an output circuit and being so connected as to be normally non-conductive, means impressing on the input circuits of the last named devices the other of said squarewave outputs, means connecting the output circuit of each of the last named devices to the control electrode of the remaining tube of a respective one of said pairs of tubes, and means coupling the remaining one of said pair of varying voltages across the output circuits of said second pair of clamping devices.

4. A system for producing a multiple display on a cathode ray tube of the outputs of a pair of radio pulse echo systems scanning through individual sectors of space, comprising, means triggering said radio echo systems to produce pulses of energy in sequential alternation, means deriving from each of said systems an angle voltage the instantaneous magnitude of which is representative of the position of the beam of the system in its scanning pattern, a pair of quadraturely acting cathode beam deflecting means for said cathode ray tube, means operating on said deflecting means to shift the cathode beam of said cathode ray'tube between two starting positions on the screen thereof in synchronism with the alternation of said pulses of energy, means generating and applyingsweep voltages to both of said deflecting means in synchronism with said pulses of energy, and means varying the magnitude of the sweep voltage applied to one of said deflecting means in sequential altemation, between values which are functions of the respective angle voltages of said radio echo systems, said sequential alternation being in synchronism with the sequential alternation of the triggering of said radio echo systems.

5. In a ground controlled approach system of the character described, an azimuth antenna, an elevation antenna, means exciting said antennas in alternation to transmit a pulse of energy, whereby there are produced azimuth and elevation energy beams in alternation, means scanning each of said antenna beams in space, means deriving a corresponding azimuth angle voltage and an elevation angle voltage the instantaneous magnitude of each of which is representative of the position of the respective beams, a cathode ray tube having a pair of quadraturely screen of said cathode ray tube in synchronism with the iransmission of successive ones of said pulses of energy, a. pair of sweep generating means operated synchronously with said transmitting means, each of said sweep generating means energizing a respective one of said deflecting means, a pair of sweep voltage generating channels in one of said sweep generating means, means energizing one of said channels to produce a sweep voltage in syn- :hronism with the transmission of said energy pulses forming said azimuth beam, means energizing the other of said channels to produce a sweep voltage in synchronism with the transmission of said energy pulses forming said elevation beam, means applying said azimuth angle voltage to said one channel to control the magnitude of the sweep voltage produced thereby, means applying said elevation angle voltage to the said other of said channels to control the magnitude of the sweep voltage produced thereby, and means combining outputs of said channels of said second sweep generating means to produce a sweep voltage with sequentially alternating amplitudes varying in accordance with the position of said antenna beams in space.

6. A system for producing a multiple display on a cathode ray tube of the outputs of a pair of radio pulse echo systems scanning through individual sectors of space, comprising: means triggering said radio echo systems to produce pulses of energy in sequential alternation, means deriving from each of said systems an angle voltage the instantaneous magnitude of which is representative of the position of the beam of the system in its scanning pattern, a pair of quadraturely acting cathode beam deflecting means for said cathode ray tube, means operaton said deflecting means to shift the cathode beam of said cathode ray tube between two starting positions on the screen thereof in synchronism with the alternation of said pulses of energy, one of said cathode beam deflecting means being operable to deflect said cathode beam along a time base coordinate and the other being operable to deflect said cathode beam along an expansion coordinate, means generating and applying sweep voltages to both of said deflecting means in synchronism with said pulses of energy, and means varying the magnitude of the sweep voltage applied to said expansion coordinate deflecting means in sequential alternation, the variation of said magnitude alternating as a function of the respective angle voltages of said radio echo systems, said sequential alternation being in synchronism with the sequential alternation of the triggering of said radio echo systems.

7. In a ground controlled approach system of the character described, an azimuth antenna, an elevation antenna, means exciting said antennas in alternation to transmit a pulse of energy, whereby there are produced azimuth and elevation energy beams in alternation, means scanning each of said antenna beams in space, means deriving a corresponding azimuth angle voltage and an elevation angle voltage the instantaneous magnitude of each of which is representative of the position of the respective beams, a cathode ray tube having a pair of quadraturely acting cathode beam deflecting means, means operable upon said beam deflecting means to position said cathode beam in one starting position on the screen of said cathode ray tube coincident with the transmission of each of said pulses of energy from said 16 azimuth beam transmitting means and to position said cathode beam in another starting position on said screen of said cathode ray tube coincident with the transmission of each of said pulses of energy from said elevation beam transmitting means, one of said cathode beam deflecting means being operable to deflect said cathode beam along a time base coordinate and the other being operable to deflect saidtcathode beam along an expansion coordinate, a first sweep generating means operable to energize said time base cathode beam deflecting means, a second sweep generating means operable to energize said expansion cathode beam deflecting means, means energizing said first sweep generating means to produce a sweep voltage in synchronism with the transmission of each of said pulses of energy, a pair of sweep voltage generating channels in said second sweep generating means, means energizing one of said channels to produce a sweep voltage in synchronism with the transmission of energy pulses forming said azimuth beam, means energizing the other of said channels to produce a sweep voltage in synchronism with the transmission of pulses forming said elevation beam, means applying said azimuth angle voltage to said one channel to control the magnitude of the sweep voltage produced thereby, means applying said elevation angle voltage to the said other of said channels to control the magnitude of the sweep voltage produced thereby, and means combining outputs of said channels of said second sweep generating means to produce a sweep voltage with sequentially alternating amplitudes varying in accordance with the position of said antenna beams in space.

8. A system for producing a multiple display on a cathode ray tube of the outputs of a pair of radio pulse echo systems having outputs occurring in pulse to pulse alternation, comprising a pair of quadraturely acting cathode beam deflecting means for said cathode ray tube, means operating on said deflecting means to shift the cathode beam between two starting positions on the screen thereof in synchronism with the alternation of said outputs, means generating and applying sweep voltages to both of said deflecting means in synchronism with the pulses of energy emitted by said pulse echo systems, means varying the magnitude of the sweep voltage applied to one of said deflecting means as a function of the orientation of the beam of the output producing pulse echo system, and means operable upon said cathode ray tube to clip normally overlapping portions of the displays forming said multiple display, said clipping means comprising a channel to which said sweep voltage applied to one of said deflecting means is applied, means in said channel blocking alternate excursions of said sweep voltage, means clipping the remaining excursions of said sweep voltage at a selected level, means deriving from said clipped voltage a square waveform the excursions of which have leading edges occurring at the time whenthe excursions of said sweep voltage reach said selected voltage level, and means applying said square waveform to said cathode ray tube in a manner to blank the cathode ray beam of said tube for the duration of each of said excursions thereof.

References Cited in the file of this patent UNITED STATES PATENTS

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