This question asks about a specific type of signal distortion that occurs when the lower sideband of a signal interferes with or overlaps the original baseband frequencies. Let's break down the concepts to understand the distortion.

Understanding Baseband and Sidebands

A baseband signal is the original information-carrying signal, typically containing frequencies starting from zero Hertz (0 Hz) up to a certain maximum frequency.

When a baseband signal is modulated (shifted to a higher frequency, like for radio transmission), it creates new frequency components called sidebands. These include the Upper Sideband (USB) and the Lower Sideband (LSB). The LSB contains frequency components that are typically below the carrier frequency.

Signal Distortion from Sideband Overlap

The scenario described—where the lower sideband overlaps the basebands—indicates that frequencies originally intended to be in the lower sideband are appearing within the original frequency range of the baseband signal. This mixing or overlap corrupts the original information.

This type of distortion is characteristic of issues that arise during signal sampling or certain types of modulation, particularly in digital signal processing. When a signal is sampled, its spectrum is replicated. If the sampling rate is not high enough relative to the signal's bandwidth (specifically, if it's below the Nyquist rate), these spectral replicas can overlap. This phenomenon, where higher frequencies are incorrectly represented as lower frequencies due to undersampling, is known as aliasing.

In the context of the question, the overlap of the lower sideband into the baseband region is a direct consequence or manifestation of aliasing. The frequencies from the lower sideband effectively "fold" back into the baseband spectrum.

Evaluating the Options

• Cross-Over Distortion: This type of distortion occurs in electronic amplifiers (particularly Class B amplifiers) when the output signal momentarily cuts off during the transition between the positive and negative halves of the input waveform. It is unrelated to sideband overlap.
• Aliasing: This distortion occurs when a continuous-time signal is sampled at a rate insufficient to accurately represent its frequency components. Higher frequencies "masquerade" as lower frequencies, causing spectral overlap. This matches the description of the lower sideband overlapping the baseband.
• Crosstalk: This refers to unwanted signal coupling or interference between different communication channels or signal paths. While it involves signal overlap, it's not specifically defined by the lower sideband overlapping the baseband in the context described.
• None of these: Since Aliasing accurately describes the phenomenon, this option is incorrect.

Therefore, when the lower sideband overlaps the basebands, the distortion is called Aliasing.