Radio navigation apparatus and filters for use therein

Claim 1

IN NAVIGATION APPARATUS FOR A CRAFT, THE COMBINATION OF MEANS FOR DERIVING A SIGNAL IN ACCORDANCE WITH DISPLACEMENT O OF THE CRAFT FROM A PREDETERMINED PATH, AND A FILTER RESPONSIVE TO SAID SIGNAL TO PROVIDE AN OUTPUT REPRESENTATION OF THE VALUE OF A VARIABLE OF SUBSTANTIALLY ACCORDING TO: OF=O/(1+KRD) WHERE D IS AN OPERATOR REPRESENTATIVE OF DIFFERENTIATION WITH RESPECT TO TIME, AND KR WHICH HAS THE DIMENSION OF TIME, IS A POSITIVEVALUED FUNCTION OF OF, THE RATE OF CHANGE OF KR WITH THE MODULUS OF OF BEING NEGATIVE THROUGHOUT A PREDETERMINED RANGE OF VALUES OF THE MODULUS OF OF EXTENDING FROM ZERO AND BEING SUBSTANTIALLY ZERO BEYOND THIS RANGE, SAID FILTER INCLUDING MEANS TO PROVIDE A REPRESENTATION OF THE RATE OF CHANGE OF THE OUTPUT REPRESENTATION OF THE VARIABLE OF, FEEDBACK MEANS FOR PROVIDING IN SAID FILTER NEGATIVE RATE-FEEDBACEK IN ACCORDANCE WITH SAID REPRESENTATION OF THE RATE OF CHANGE OF THE VARIABLE OF, SAID FEEDBACK MEANS BEING CONTROLLABLE TO VARY SELECTIVELY THE DEGREE OF NEGATIVE RATE-FEEDBACK, AND MEANS OPERATIVELY COUPLED TO THE FEEDBACK MEANS TO CONTROL THE DEGREE OF NEGATIVE RATE-FEEDBACK IN ACCORDANCE WITH THE MAGNITUDE OF SAID OUTPUT REPRESENTATION.