A single impulse in the time waveform will produce what in the spectrum?

When a single impulse occurs in the time waveform, it generates a wide frequency spectrum in accordance with the principles of Fourier analysis. This results in a broad range of frequencies being excited, which can elevate the noise floor in the frequency domain.

The key reason for a raised noise floor relates to how an impulse acts as a transient event that introduces many frequencies simultaneously. The energy from the impulse doesn't just resonate at a specific frequency but can spread across a range of frequencies. This behavior is because an impulse contains both low and high frequency components, which contributes to the overall energy in the spectrum.

In contrast to raised noise floor, the other options refer to specific types of harmonic content that typically arise from periodic waveforms. Even harmonics and odd harmonics are associated with the periodic repetition of waveforms — even harmonics arise from symmetrical waveforms, while odd harmonics usually result from non-symmetrical, or square-like signals. Half-order harmonics involve combinations of fundamental frequencies that don’t directly correlate with the transient nature of an impulse.

Thus, in the case of a single impulse, the presence of all these frequencies pushes the overall energy level higher, contributing to the raised noise floor in the spectrum.