Display of variable length vectors

A variable length vector display system allows visual indication of the sd and direction of aircraft or moving vehicles, maintaining a constant illumination on the face of a cathode ray tube independent of the vector length or vector movement. The vector length from the target vehicle coordinate points to the predicted intercept coordinate points are displayed. Voltages defining the origin and the end point of a vector to be displayed are coupled through respective comparator and arithmetic units, scaled to provide a deflection factor, multiplied, and coupled through respective controlled integrator circuits. The integrators are controlled by a variable gate which operates as a function of the input signal, thereby varying the on-off time of the integrators for simultaneous operation. Output signals from the integrator circuits are coupled to respective X and Y deflection circuits of a cathode ray tube load. In conjunction with the input zero reference or origin signal the signals are combined to provide the appropriate X and Y deflection potential for the tube.

BACKGROUND OF THE INVENTION 
Display systems often face the problem of painting a vector between any two 
points on a cathode ray tube screen. Depending on characteristics such as, 
time available to draw the vector, the refresh rate of the vector, the 
rate of change of the orientation of the vector, tube characteristics, and 
vector length; it is possible to get serious variations in intensity 
levels for individual vectors. The long vector being plotted may be hard 
to discern, while the short vector may exceed the safe operating point for 
the tube. In prior art systems, a simple charging voltage proportional to 
the X and Y coordinates of the vector is applied to integrators which are 
controlled by a fixed gate generator. Such a system can result in serious 
variations in writing speed and illumination intensity. 
SUMMARY OF THE INVENTION 
The variable length vector display system maintains a constant cathode ray 
tube illumination intensity when writing a vector of any length on the 
viewing screen of the cathode ray tube. The linear sweep outputs of X and 
Y operational amplifier sweep generators, integrators, are controlled by a 
variable gate generator which operates as a function of the combined 
coordinate input signal voltages to provide a vector length display having 
substantially uniform writing speed and illumination intensity.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to the drawing, a first pair of input voltages X.sub.0 and 
X.sub.1, are applied to the input terminals of a comparator 11; and, a 
second pair of input voltages Y.sub.0 and Y.sub.1, are applied to the 
input terminals of a comparator 13. These input voltages may come from a 
conventional radar receiver and may, for example, be indicative of the 
speed and direction of an aircraft. Voltages X.sub.0 and Y.sub.0 define 
the origin or start point of a vector to be displayed, while voltages 
X.sub.1 and Y.sub.1 define the end point, or head, of the vector to be 
displayed. The output signals from comparators 11 and 13 are .DELTA.X and 
.DELTA.Y and represent the difference between the respective input 
voltages. Thus, .DELTA.X = X.sub.1 - X.sub.0 and .DELTA.Y = Y.sub.1 - 
Y.sub.0. The .DELTA.X signal is simultaneously applied to a scaling 
amplifier 15 and to an arithmetic unit 17. The .DELTA.Y signal is 
simultaneously appled to a scaling amplifier 19 and to arithmetic unit 17. 
Arithmetic unit 17 is of conventional design and may include, for example, 
voltage multipliers employing feedback for forming an output signal, 
L.sub.v, indicative of the square root of the sum of the squares of the 
input signals. Thus, L.sub.v =.sqroot..DELTA.X.sup.2 + .DELTA.Y.sup.2. The 
output signal from arithmetic unit 17 is coupled directly to a variable 
gate generator 21 and, is coupled by way of an invertor 23, to multipliers 
25 and 27. 
Scaling amplifiers 15 and 19 simply modify the input signals by a constant, 
K, which is a deflection factor. Thus, the output signals from scaling 
amplifiers 15 and 19 are K.sub.x .DELTA.X and K.sub.y .DELTA.Y. It 
follows, therefore, that the output signals from multipliers 25 and 27 
are, respectively, K.sub.x .DELTA./l.sub.v and K.sub.y .DELTA.Y/L.sub.v. 
These signals are applied to respective integrators 29 and 31 whose 
integration time is controlled by variable gate generator 21 operating 
respective unijunction transistors 30 coupled across integrating 
amplifiers and capacitors C. The output signal from integrator 29 is 
applied to the deflection circuit 33 of a display tube 35, while the 
output signal from integrator 31 is applied to the deflection circuit 37 
of tube 35. The coordinate voltages X.sub.0 and Y.sub.0 of the origin of 
the vector to be displayed are applied to deflection circuits 33 and 37 
respectively. In response to the voltage input signals, the circuit is 
effective to control the intensity of the display on display tube 35 
regardless of the length of the vector displayed. Prior art systems would 
simply apply a charging voltage, proportional to .DELTA.X and .DELTA.Y, to 
integrators 29 and 31 which would be under the control of a fixed gate 
generator. Such prior art systems can result in serious variations in 
writing speed and illumination intensity. 
Deflection circuits 33 and 37 may be electrostatic or electromagnetic 
deflection means, such as deflection plates or deflection coils, as is 
well established in the art. Summing amplifiers 32 and 34 are coupled to 
receive the outputs from integrators 29 and 31 respectively and to receive 
the respective X.sub.0 and Y.sub.0 inputs coupled to the deflection 
circuits for developing the respective deflection voltages across the tube 
35. The effective writing speed (WS.sub.EFF) on the face of tube 35 is a 
function of the individual writing speeds in the X and Y direction. Thus, 
EQU WS.sub.EFF =.sqroot.(WS.sub.x).sup.2 + (WS.sub.y).sup.2 . (1) 
Assuming linearity and unity gain in the deflection system, the individual 
writing speeds WS.sub.x and WS.sub.y are directly related to the sweep 
integrator slope. Thus, 
##EQU1## 
K.sub.x, K.sub.y, R, and C are known constants, therefore the writing 
speeds in the X and Y directions are directly proportional to .DELTA.X and 
.DELTA.Y, and the effective writing speed is proportional to the vector 
length L.sub.v, where 
EQU L.sub.v =.sqroot.(.DELTA.X).sup.2 + (.DELTA.Y).sup.2 . (3) 
rearranging terms and defining or limiting K.sub.x = K.sub.y = K, it is 
apparent that 
##EQU2## 
By solving equation 3, the compensation factor L.sub.v is obtained from 
arithmetic unit 17 which corrects for writing speed variations. The 
respective X and Y charging voltages are multiplied by the inverse of this 
factor (1/L.sub.v) so that the new writing speeds become 
##EQU3## 
and, therefore, substituting equation 5 into 1, it is apparent that 
##EQU4## 
The vector length L.sub.v, calculated by arithmetic unit 17, is applied as 
an input to variable gate generator 21 wherein it is used to control the 
integration time of integrators 29 and 31. The total integration time 
.DELTA.t.sup.1 is, therefore, .DELTA.t.sup.1 = .DELTA.tl .sub. v where 
.DELTA.t is initially set for some minimum length vector. Thus, the 
voltages out of integrators 29 and 31 are, respectively, 
##EQU5## 
Thus the sweep generator output voltages supply the appropriate variable X 
and Y vector length signals and the sweep generators or integrators are 
variably controlled to provide uniform writing speed and illumination 
intensity of the cathode ray tube. 
Although a particular embodiment and form of this invention has been 
illustrated, it is apparent that various modification and embodiments of 
the invention may be made by those skilled in the art without departing 
from the scope and spirit of the foregoing disclosure. Accordingly, the 
scope of the invention should be limited only by the claims appended 
hereto.