Interference reducing circuit for avoiding effects of e.g. atmospheric or industrial EM interference on radio transmission

摘要

The interference reducing circuit, uses a correction channel to correct the noise picked up with a radio signal, and includes a detector (17) and two multipliers (18,19) which may be analogue or digital forming synchronous demodulators. These are supplied with two 90 deg. phase-offset sinusoidal voltages (VA,VB) and are followed by two passband filters (20,21) which are then fed to two amplifiers (22,23). The circuit is used to detect the ambient electromagnetic noise in a particular environment, and the signal produced is subtracted from the main radio signal in order to produce a signal which is less subject to data corruption caused by the noise signals, using a numerical statistical method to obtain optimal correction.