Because all digital scopes operate on sampled data, they are subject to aliasing. An alias is a false reconstruction of the signal caused by under-sampling the original. An alias will always be displayed as a lower frequency than the actual signal. Some vendors employ proprietary techniques to minimize the likelihood of this problem occurring. Be sure to test any scope being considered for purchase on your worse-case signal to see if it produces a correct or aliased display. Do not simply test it with a single-shot signal that will be captured at the scope’s fastest sweep speed because this will fail to test the scope’s ability to correctly display signals that require slower sweep speeds.
8. Analysis functions? Digital oscilloscopes with their embedded microprocessors have the ability to perform mathematical operations that can give additional insight into waveforms. These operations often include addition, subtraction, multiplication, integration, and differentiation. An FFT can be a powerful tool, but do not be misled into thinking it is a replacement for a spectrum analyzer. Be sure to check the implementation of these features in any scope being considered. For example, does the FFT provide a selection of window functions? Are these analysis functions implemented with a control system that only their designer could apply?