Blade control system with reactive pickup

Claim 1

IN A VEHICLE CONTROL SYSTEM, A VEHICLE HAVING AN ADJUSTABLE BLADE, MEANS FOR MOVING SAID BLADE RESPONSIVE TO AN ELECTRICAL SIGNAL, A LEAD LINE DISPOSED ABOVE A SURFACE TO BE LEVELED AT A PRESELECTED ELEVATION ABOVE THE DESIRED LEVEL SURFACE, SAID LINE BEING ELECTRICALLY CONDUCTIVE, SERIES CONNECTED REACTANCE MEANS AFFIXED TO SAID BLADE, A SOURCE OF REFERENCE FREQUENCY, MEANS FOR COUPLING SAID SOURCE OF FREQUENCY TO SAID REACTANCE MEANS, SAID REACTANCE MEANS BEING DISPOSED ON DIAMETRICALLY OPPOSITE SIDES OF SAID CONDUCTIVE LINE WHEREBY VARIATION IN THE LOCATION OF SAID LINE BETWEEN SAID REACTANCE MEANS WILL CAUSE A VARIATION IN THE CURRENT PHASE WITHIN THE REACTANCE MEANS, MEANS FOR COMPARING THE CURRENT PHASE WITHIN SAID REACTANCE MEANS WITH THE REFERENCE FREQUENCY, SAID LAST NAMED MEANS PRODUCING AN OUTPUT SIGNAL REPRESENTATIVE OF SAID COMPARISON, AND MEANS RESPONSIVE TO SAID OUTPUT SIGNAL FOR ADJUSTING SAID BLADE.