说明：  The file calculates and plots FM noise sidebands for a carrier. It also does sinusoidal modulation. This simple way of adding noise to a carrier is useful for simulation of PLLs. It turns out, though, that the mean of the randn function is not as close to zero as it could be, and this causes the fft to generate extra sideband energy, which makes it appear as if the noise is not what would be expected. This program gets around this by adding a fudge factor to the randn results to eliminate this problem. It took me ages to figure this out, I hope to reduce a similar effort for others.