Circuit and method for determining the type of noise or interference in a FM modulated broadcast signal receiver

摘要

The method determines interference signals in the frequency modulated received signal of a radio receiver such as a car radio by analysing the varying voltage component in the field strength signal. The varying voltage component undergoes one or more of the following steps. Does it include a frequency identical to the pilot tone frequency How frequent is the pilot tone frequency present How frequent are different frequencies present The test results provide an individual signal for the presence of a multi-path interference, a same channel or adjacent channel interference or no interference. The apparatus includes two narrow band filters whose inputs are connected to the field strength signal output of the intermediate frequency stage of the radio receiver. One filter has an average frequency of 19 kHz and the other has a different frequency. A rectifier (GI) is connected to the filters and its outputs are connected to the input of a comparator (Comp).