Phantastron

Abstract: 764,478. Electric analogue calculating systems. MINISTER OF SUPPLY. July 21, 1954 [Aug. 4, 1953]; No. 21552/53. Class 37. An electrical computing device for determining the modulus of the product of two singlevalued functions comprises an oscillator, means for controlling the frequency of the oscillator according to the modulus of one function and a digital counter connected to the oscillator for providing an output which is indicative of the number of cycles of oscillation of the oscillator occurring during an interval of time the length of which is dependent on the modulus of the other function. In one arrangement, Fig. 1, the device is used to obtain in digital form the cartesian co-ordinates of an object detected by a radar, the received signals of which are fed to a storage tube 5. The time-base 7 of the reading part of the storage tube 5 is triggered by a master pulse generator 8, and after a time interval representative of the range of the object an echo pulse passes through a gate 9, which is normally open, to a pulse generator 10 which produces a square wave output each time a pulse is fed to it. The aerial 1 of the radar is connected through a shaft 21 to a variable condenser 22 forming part of the tuned circuit of an oscillator 23, the output of which is fed together with the output of a fixed frequency oscillator 24 to a mixer 25. The plates of condenser- 22 are so shaped that the output of mixer 25 has a frequency proportional to the modulus of the sine of the azimuthal angle of the aerial. Oscillators 23 and 24 are each triggered by the master pulse generator 8. The output of mixer 25 is connected to a squarer 26 which produces a square wave output once per cycle of oscillation of the mixer output and feeds a binary counter 27. Each stage of counter 27 is connected to one of the gates 11-20 in such a way that when the stage is in one state the gate is open, and when it is in the other state the gate is closed. Thus when the range pulse from generator 10 is fed simultaneously to all the gates 11-20 the output indicator in binary form the product of the range and the rise of the azimuth angle. The other cartesian co-ordinate can be obtained from a similar arrangement in which the mixer output is arranged to be proportional to the cosine of the angle. Ambiguity in sign of the co-ordinates can be resolved by a commutator 31 driven by shaft 21 and connected through a trigger circuit 32 to a gate 33. A pulse generator 34 closes gate 9 when pulses are passing from squarer 26 to counter 27 and thus prevents a wrong indication being given when the counter is changing its state. In another embodiment, Fig. 3 (not shown), for computing the product of two numbers, the variable condenser 22 is adapted so that the output from mixer 25 varies linearly with angular rotation of the condenser, and the multiplicand can be set up on a calibrated scale co-operating with the condenser spindle. The storage tube is replaced by a phantastron circuit which triggers the oscillator and provides an output pulse after a time interval controlled by a potentiometer which can be calibrated in terms of the multiplier. Specification 582,758, [Group XL], is referred to.