Broadband

Typical broadband signals include white noise, pink noise, impulses, and chirp signals.

The following figure shows the simulated frequency response function for a four-degree-of-freedom system.

The peak at 17.6 Hz has a magnitude roughly 1,000 times larger than the peak at 5.8 Hz. To use the broadband measurement, use broadband excitation to excite the entire frequency range of interest to measure the frequency response. This situation forces you to set the input range so that the overall response does not overload the DUT or the acquisition device. Therefore, when you measure the response at 5.8 Hz, you lose 60 dB of the measurement dynamic range. The swept-sine measurement enables you to tailor the excitation amplitude to the specific test frequency, preserving the full measurement dynamic range.

The broadband measurement is limited to a linearly-spaced frequency resolution determined by the sampling rate and the block size. When the response changes rapidly, this frequency resolution may not yield enough information about the dynamic response. Also, a linear resolution might yield an excessive amount of information in frequency regions where the dynamic response is relatively constant. The stepped swept-sine measurement has the ability to test arbitrary frequency resolutions that are linear, logarithmic, or adapted to the dynamic response of the DUT. When the frequency resolution is adapted to the DUT dynamic response, you can test more frequencies in regions where the dynamic response is of interest to the application and less where it is not.

The main benefit of a swept-sine measurement is the ability to measure harmonic distortion simultaneously with a linear response. A broadband measurement offers a speed advantage for broadband measurements with many test frequencies.