Abstract: A method and a circuit arrangement for determining the entry and/or exit of a vehicle into or out of a predetermined monitoring zone, which is defined by at least one inductive measuring loop whose change in inductance, which occurs as a result of the entry of a vehicle into the monitoring zone or the exit of a vehicle out of the monitoring zone, is used to control the oscillation frequency of an oscillator circuit is disclosed. In this method a measuring signal which corresponds to the oscillation frequency of the oscillator circuit and a reference signal which corresponds to a reference oscillation frequency are subtracted from one another. The difference signal thus formed is processed in an analysis device for display purposes.

Abstract: A circuit arrangement for the production of a control signal, in particular a level regulation signal, in a receiving channel which is subject to interference, forms an amplitude-dependent control signal from the phase coded input signal. In the receiving channel a frequency regulating circuit has an oscillator which is synchronized by means of the received signal and the received signal is superheterodyned with the output signal of the oscillator in one mixer, directly, and delayed by 90.degree. in another mixer. The mixed products are then fed through low-pass filters to obtain signals which indicate the frequency shift between the input signal frequency and the oscillator frequency, which signals are converted in a third mixer and serve for tuning the oscillator. The output signals obtained from the outputs of the two first-mentioned mixers, after being fed through low-pass filters, are squared and combined in a difference stage.