Method for operating optical heterodyne receivers with a control device which has a capture range to regulate an intermediate frequency of the receiver at an ideal value and a receiver to carry out a method of this type

摘要

An automatic intermediate frequency controller is required in order to guarantee optimum operation of optical heterodyne receivers. This controller has a specific capture range within which the correct intermediate frequency is achieved following activation of the controller. Since the frequency uncertainty of the transmitter or local oscillator is generally greater than the capture range, presetting of the local oscillator frequency is required before the controller is activated. Solutions are known for FSK-modulated data signals without data-synchronous polarisation shift keying, whereas problems occur in the case of signals with data-synchronous polarisation shift keying. These problems are solved according to the invention on the one hand by presetting the local oscillator frequency with the aid of a sampling of the mean time value of an output signal of a demodulator of the receiver to a maximum and, on the other hand, by changing over between two discriminators of the receiver which are connected upstream of the controller and which have two different characteristics. IMAGE