FFT - Xilinx System Generator Block

Hi there,

I'm trying to execute a simple fft example of a pure sinewave using the Xilinx System generator block in Simulink. I already know that the result is a complex number, what I've not found is the right way to plot my results.

I expect, given a sinewave (i.e. at 50 Hz), to have two peaks in my spectrum at -50 and 50 Hz.

My questions are:

1. Why the fft result is multiplied by a factor given by the number of samples of the transform?
2. How can I plot correctely the frequency spectrum of the fft result directly in simulink, or in matlab?

I attach the model and the result I obtained, with the complex plot of the fft result and the uncorrect spectrum. The samlipng frequency is 1 MHz.

I wait for some kind help.

Regards,

Giuseppe