I have a power source that is supposed to be low noise, and i want to verify that the data the company sent me is indeed accurate. In order to do this, i want to reproduce their graph showing current noise density (nA/root(Hz)) on the Y axis, and Hz on the X axis. I am an undergraduate physics student, and i am not familiar with making these types of measurements. The method i have been using is connecting the source up to a dummy load (provided by the company for testing), to a pre-amp, to a oscilloscope. I took data off the oscilloscope but had issues in trying to understand how to get the correct values on the axis. An FFT seems needed, btu i am using igor for data processing and It only requires one set of data for an FFT and doesnt seem to require a time axis which perplexs me. It also doesnt help that i have not studied the math behind FFT's quite yet. Does anyone have any suggestions? I have access to a Spec. Analyzer if thats useful, but it goes from 9KHz to 29.5Ghz, and the graph id like to reproduce goes from 0 to 10^5Hz.