Vehicle detection and speed measuring apparatus

Claim 1

IN A SYSTEM FOR SELECTIVELY MEASURING THE SPEEDS OF VEHICLES MOVING IN EITHER OF TWO GENERALLY OPPOSITE DIRECTIONS THROUGH A DETECTION ZONE DEFINED BY A BEAM OF SOUND ENERGY DIRECTED WITH A SUBSTANTIAL COMPONENT GENERALLY PARALLEL TO THE DIRECTION OF TRAVEL OF SAID VEHICLES THE COMBINATION COMPRISING, MEANS FOR TRANSMITTING SAID SOUND ENERGY WITH A PREDETERMINED FREQUENCY, RECEIVING MEANS FOR RECEIVING SAID SOUND ENERGY FOLLOWING ITS REFLECTION FROM SAID VEHICLE WITH ITS FREQUENCY SHIFTED TO ONE SIDE OR THE OTHER OF SAID PREDETERMINED FREQUENCY ACCORDING TO THE DIRECTION OF TRAVEL OF SAID VEHICLE AND BY AN AMOUNT PROPORTIONAL TO THE COMPONENT OF VEHICLE VELOCITY PARALLEL TO THE DIRECTION OF SAID SOUND BEAM, SAID RECEIVING MEANS INCLUDING MEANS FOR CONVERTING SAID RECEIVED SONIC ENERGY TO AN ELECTRICAL SIGNAL HAVING FREQUENCY COMPONENTS CORRESPINDING TO THOSE IN THE REFLECTED SONIC ENERGY, SAID RECEIVING MEANS ALSO INCLUDING FILTERING CIRCUIT MEANS HAVING SAID ELECTRICAL SIGNAL APPLIED THERETO AND BEING TUNED TO PASS THOSE FREQUENCY COMPONENTS WHICH HAVE BEEN DOPPLER SHIFTED IN A PARTICULAR DIRECTION WITH RESPECT TO SAID PREDETERMINED FREQUENCY AND RESULTING FROM THE PASSAGE THROUGH SAID DETECTION ZONE OF A VEHICLE MOVING IN A SELECTED ONE OF SAID TWO OPPOSITE DIRECTIONS, AND MEASURING MEANS DISTINCTIVELY CONTROLLED BY THE OUTPUT OF SAID FILTERING MEANS ACCORDING TO THE AMOUNT OF THE FREQUENCY SHIFT OF THE REFLECTED SIGNAL RELATIVE TO SAID PREDETERMINED FREQUENCY FOR GIVING A DISTINCTIVE INDICATION OF VEHICLE SPEED.