Abstract: A system and method for adjusting the frequency of operation of a radio frequency circuit including an inductive loop having an adjustable exposed inductor portion is provided. The frequency of operation of the circuit is first detected with means for detecting a parameter relating to and representing the frequency of operation. The adjustable inductor portion is associated with a selectively movable actuator device coupled to the frequency detecting means and a source of signals representing a predetermined frequency of operation for the circuit. A control circuit means, preferably a computer, is coupled to the detecting means and to the source of signals to provide an output control signal when the detected frequency of operation bears a predetermined relationship to the predetermined frequency of operation.

Abstract: Tuning elements are provided for use in varying the inductance of the oscillatory circuits of the transmitter and receiver units of garage door actuators operating at ultra-high frequencies. Each oscillatory circuit is a closed loop circuit fabricated on a printed circuit board. The closed loop circuit comprises a pair of printed circuit conductive paths having a fixed capacitor connected across one of the ends thereof and a discrete generally U-shaped wire connected across the other of the ends thereof. The conductive paths and the U-shaped wire comprise the inductor of the oscillatory circuit. By bending the discrete U-shaped wire at its connections with respect to the plane of the printed circuit board, the inductance of the oscillatory circuit in each unit can be adjusted as needed so that they both operate at the same resonant frequency.

Abstract: The invention relates to a passive reply device for use, for example, in automatic wireless transmission of multi-place numerical information between it and an active interrogation device which are movable with respect to one another, particularly for track-bound transport apparatus, which comprises a high frequency line section having a high frequency antenna at one end, and short circuited at its opposite end, and a plurality of high frequency coaxial resonators extending transversely to and carried by such line section, with a number of resonators being proportional to the number of places of the information to be transmitted. The resonators consist of individual elements which are inserted in appropriate bores of the line section with a press fit. The tuning of the individual resonators is determined by the particular shape of the bottom wall of each resonator, with the resonators otherwise being similar in construction.