What is line spectra referring to in signal analysis?

• A. Line spectra plot amplitudes and phases of frequency components after Fourier representation.
• B. Line spectra plots time-domain instantaneous amplitude.
• C. Line spectra show only the DC component.
• D. Line spectra are derived from non-periodic signals only.

Answer: (A)

Line spectra represent the frequency-domain content of a signal as discrete lines at specific frequencies. Each line corresponds to a sinusoidal component revealed by a Fourier representation, with its height showing the component’s amplitude and its angle giving the component’s phase. For periodic signals, these lines appear at harmonic frequencies of the fundamental; non-periodic signals tend to produce a continuous spectrum rather than discrete lines. The DC component is just one line at zero frequency, but line spectra overall describe the distribution of energy across all frequencies, not just a time-domain amplitude or a single value.