Patent GB-1414990-A (GB)
Title: Communication apparatus
IPC: G08G1/09
Filed: 1972-10-24
Abstract: 1414990 Radio signalling; inductive signalling INFORMATION IDENTIFICATION CO Inc 24 Oct 1972 [28 Jan 1972] 49045/72 Headings H4L and H4U [Also in Division G4] Apparatus for providing communication between a first object and a second object comprises means in the first object for generating and transmitting a transmit signal, means in the second object for receiving the transmit signal and providing an output signal having a frequency derived from the frequency of the transmit signal, an identification encoder connected to the receiver in the second object and arranged to receive the receiver output signal, the encoder having a predetermined code encoded therein and arranged to provide an output signal indicative of the predetermined code in response to the receiver output signal, and a signal controller inducting gating means for receiving the receiver output signal and the identification encoder output signal, the grating means being arranged to combine the receiver output signal and the encoder signal to encode the predetermined code in the received transmit signal to provide an encoded emitted signal, and means in the first object for receiving the emitted signal. In the preferred embodiment, apparatus for measuring the speed of a moving vehicle and for automatically recording the excess speed together with the vehicle registration number comprises means in the vehicle actuated by an A.C. signal from a roadside transmitter to send back to a roadside receiver the same signal divided and code-modulated to represent the number of the vehicle, there being two such roadside transmitters and receivers whereby according to the time interval between the two received signals, the speed of the vehicle is determined and a roadside processor unit causes an amplitude modulation of the signal emitted which is detected in the vehicle to illuminate an alarm to tell the driver of his excess speed and that this has been stored in a roadside memory of the processor unit together with his registration number for the preparation of a fine.  Vehicle mounted transceiver-comprises a threshold device to pass the detected roadside signal to a divide by N count, the output of which is taken to an AND gate together with the clocked output from a recycling P-stage shift register storing the number of the vehicle, the clocking of the shift register being effected by the output of a divide by M counter the input of which is the output of the N stage counter. The output of the gate is thus the code-modulated signal. An amplitude modulation detector allows the functioning of the M-counter in these conditions but disables this when the received signal from the roadside transmitter is amplitude modulated, whereby a further counting chain is enabled to provide a pulse to switch on a dash-board lamp via a holding relay. Roadside processor-comprises two receivers for receiving the code-modulated signal form the car respectively derived from each of the two transmitters. Each receiving unit comprises means for deriving the clocking signal of the same frequency and phase as that used to read out from the shift register in the vehicle and this is used via a gate circuit to clock a shift register to read in the received code-modulated signal from the vehicle which is presented via a further gate. In order to prevent erroneous readings stages "O" and "P" of this shift register are compared and since the received signal is repeatable every P pulses, these stages should be identical. After e.g. R clocking pulses without disparity between these stages a counter provides an enabling output to a gate and when a certain sequence of the register is detected by a set of exclusive OR gate comparators indicative that the vehicle code is correctly positioned therein, a further output is applied to the gate which resets a flip-flop which had previously been enabling the two input gates. The arrival of this signal causes the contents of the shift register to be clocked out into a buffer store and also starts a counter counting clock pulses, which counting is terminated by the arrival of the pulse from the second receiver unit. If the count is greater than that which represents a speed limit, this is passed to the buffer store alongside the registration number and the amplitude modulated carrier signal is sent back to the vehicle. The buffer store is periodicially read-out to a central computer for the preparation of fines. The numbers stored in the shift registers of the two receiver units are compared prior to read-out to check that the same vehicle has been sensed.