Puzzler

Sam was new to VisSim and wanted to plot a nice, unit amplitude sin wave as a starter exercise. But all he got was a slowly increasing spray of noise at ~10e-13 in amplitude. Not a sin to be seen anywhere. What did Sam do?

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Mike Borrello, Carl Toft and Mark Malloy
The best answer was from Mike:


Dear Puzzler,

Sam unfortunately never heard of Nyquist or Shannon's sampling theorem. When he set up his diagram he neglected to set the simulation step size fast enough to sample the frequency he set for the sine wave. But more specifically he set the step time equal to the Nyquist frequency of the sign wave - one half the frequency of the sine wave. What Sam is seeing is an aliased signal of the sine wave that - say for example is 1000 Hz sampled at 500 Hz. This causes an alias of the sine wave at zero Hertz. The 'noise' that appears in the plot are residual errors due to the finite precision of the calculations.

Also thanks for the newsletter, and keep them coming - good work.

Many Thanks,

Mike Borrello