When a sample stream is decimated, frequency components from outside of a desired frequency band are aliased into the desired band, causing interference and loss of information. Different decimating ratios result in different frequencies aliasing into the desired frequency band. A current-mode sampling mixer 800 with capacitor banks 811 and 812 that are controlled by a digital control unit 820 with a capability to integrate and decimate an RF current at different decimating ratios is able to measure the frequency spectrum with different decimating ratios. The measured frequency spectrum is then analyzed to detect the presence of interferers aliased into the desired frequency band. The interferers can then be eliminated or avoided.