Circuit arrangement for the production of a control signal in a

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. The result is again passed through a low-pass filter and squared again before being fed to an addition stage. One input of the addition stage is obtained from the output signal of the third mixer, after squaring, and an amplitude correction stage is provided in front of another input of the addition stage to effect cancellation of the signal components arising from phase errors of the frequency regulating circuit and from the noise components in the useful signal. The interference-free output obtained is used as the control signal.