Narrow-band interference suppression circuit esp. for car radio - employs PLL and shifter to generate compensation signal at frequency of interference component but with opposite phase

摘要

The IF signal (uN) degraded by interference (uS) is added (2) to a compensation signal (uK) generated in a two-quadrant multiplier (6) of an antiphase equiv. of the interference component (uKO) and the result (um) of multiplying (7) the latter by the degraded input (1), with low-pass filtering (8). The antiphase signal is produced from the input by a phase-locked loop (4) whose output is shifted (5) by a further 90 deg. The amplitude and phase of the compensation signal may be regulated by additional loops incorporating integrators. ADVANTAGE - More effective suppression of interference from clocked electronic equipment harmonics possible without detriment to reception of useful signal.