Adaptive noise cancelling receiver

Abstract

A receiving system is described which has the capability of substantially cancelling broadband noise, such as impulse noise, atmospheric noise, electrical line noise and receiver front end noise, from a selected radio frequency passband. In a first embodiment, a desired radio frequency passband is selected and converted to a broadband intermediate frequency (IF) signal, which is applied in parallel to the inputs of first and second frequency channels. When broadband noise is present in the broadband IF signal, the first frequency channel develops a desired audio signal in the presence of an undesired first broadband noise signal, while the second frequency channel develops an undesired second broadband noise signal which is correlated with the first broadband noise signal. An adaptive transversal filter is responsive to the second broadband noise signal and to an output signal for adaptively developing an estimate of the first broadband noise. The estimate of the first broadband noise signal is subtracted from the combination of the desired audio signal and the first broadband noise signal in order to cancel out the first and second broadband noise signals and substantially develop only the desired audio signal as the output signal. When no broadband noise is present in the broadband IF signal, the adaptive filter automatically shuts itself off and the first frequency channel only develops the desired audio signal. Thus, regardless of whether or not broadband noise is present, the output signal is substantially comprised of only the desired audio signal.