Why does the amplitude of my signal cut to half+ or even less then half+ when I add noise?

Why does the amplitude of my signal cut to half+ or even less then half+ when I add noise?

Adding noise in the AFG 3000 uses a power splitter to add the noise to the signal. When you are at the highest amplitude levels of your AFG 3000, it must reduce the amplitude of the signal, in order to be able to add noise. It will halve the amplitude, because theoretically the noise could be as high as half the amplitude, and so the AFG 3000 must accommodate that possibility. Because the noise is Gaussian, however, it rarely is that high in amplitude, so measuring peak to peak will not necessarily show double the voltage.