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So I have this very basic circuit show below which I am simulating with PSpice.

enter image description here

Now, when doing the Fourier transform of $\cos(2\omega1000t)$, I expect to see two impulses(one at -1kHz and one at 1kHz), at half the amplitude of the cosine. The simulated results, however, shows the impulse at 1kHz with an amplitude of just below 1V. This is shown below:

enter image description here

My question is, why is this the case? Why is the amplitude not 500mV? I'm probably just missing something trivial.

Thanks in advance!

(Side note - why is there no pspice tag? Is this the correct form to post this question?)

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  • $\begingroup$ This should probably be on electronics.SE, since it's about the normalization used in electronics software $\endgroup$ – endolith Apr 2 '18 at 18:37
  • $\begingroup$ Also see this, it sounds very similar. $\endgroup$ – a concerned citizen Dec 29 '18 at 8:19
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PSPICE is showing the "Double Sided" Spectrum with the assumption (as it is) of a real signal. This means the spectrum is positive frequency axis only and the result will be double of what you would expect to see with a "Single Sided" Spectrum, basically matching the amplitude of the sinusoidal component represented.

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PSPICE is probably using the FFT to compute the spectrum from the time domain signal transient. You can see in your plot a small harmonic after 1.2kHz too. The windowing will add some harmomic content to your spectrum.

The 500mV value is a theoretical value assuming infinite duration for the sinewave.

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