Which method reduces unwanted signals in a radio receiver?

Employing noise filters is effective in reducing unwanted signals in a radio receiver because they are specifically designed to eliminate or minimize interference and unwanted noise without significantly affecting the desired signal. Noise filters can be implemented in various forms, such as low-pass, high-pass, band-pass, or notch filters, depending on the types of noise or interference present. By selectively allowing certain frequencies to pass while blocking others, noise filters ensure that the radio receiver can focus on the desired signal, improving overall clarity and performance.

The other methods listed do not primarily target the reduction of unwanted signals. Using a wider bandwidth can actually allow more signals to be received, which might increase interference rather than reduce it. Implementing digital encoding focuses on the representation of information rather than filtering out noise. Cross-modulation techniques involve mixing signals in a way that may introduce additional complexity and noise rather than alleviate it. Thus, employing noise filters stands out as the most effective method for unwanted signal reduction in a radio receiver context.