# Why am I seeing a negative frequency on FFT graph in Gnu Radio Companion? [closed]

I have a pretty simple flow here in GRC, but for some reason I'm seeing a negative frequency mirroring the 10khz signal that I'm generating. What's causing this negative frequency to show up in the FFT graph?

• A cosine should have a positive and negative part. $\cos(\theta) = e^{(i\theta)}/2 + e^{(-i\theta)}/2$ – learner Sep 9 '18 at 19:58
• @learner I tried changing it to Sine, but there was no difference. – Gogeta70 Sep 9 '18 at 20:27
• Any real-valued signal has a (conjugate) symmetric Fourier transform, so you'll always see a symmetric spectrum. – Matt L. Sep 9 '18 at 20:35