Does a 200 MHz bandwidth oscilloscope mean it can measure signals with frequencies up to 200 MHz?
Bandwidth is a fundamental specification of an oscilloscope. When using a 200 MHz‑bandwidth oscilloscope to measure a 1 V, 200 MHz sine wave, the measured amplitude will be attenuated to only 0.707 V. However, this simple rule does not apply to square or triangular waveforms; their spectra must be analyzed via Fourier transformation, taking into account how many lower‑order harmonics are of interest. For example, with a 40 MHz square wave, according to spectral analysis principles, you can typically resolve only up to the fifth harmonic at 200 MHz—harmonics beyond the fifth become indistinguishable, and the square wave may appear as a curve with some rounding. Of course, once a signal exceeds the oscilloscope’s bandwidth, only its amplitude is attenuated; the frequency content remains unchanged. If your primary concern is the frequency itself, such considerations are less critical: a 200 MHz square wave will still be measured at 200 MHz. When selecting an oscilloscope, to achieve a given measurement accuracy, it is generally advisable to choose a bandwidth that is at least five times the highest frequency component of the signal.
