Take the 2-minute tour ×  Imagine the varying frequency
generator, which feeds this frequency to the oscilloscope.
Oscilloscope is turned to show signal spectra with FFT. The
image on the screen of the oscilloscope is as expected: single
peak, traveling from 1 kHz to 50 kHz. Of course, my generator is
not ideal, it gives a number of harmonics with less magnitude.
But the strange thing happens: if my peak goes from 1 kHz to 50
kHz, the other peak appears at 50-60 kHz, and goes to lower
frequencies towards mine peak. At time of appear, it's hardly
noticeable, but in the end it's almost half of main frequency.
Whenever varying frequency comes to it's maximum (50 kHz), ghost
frequency almost approaches it. At this moment my generator
drops back frequency to 1 kHz, ghost frequency disappears and
process starts again. What causes such a behaviour?  PS: I think
it's more mathematical question, rather then physical or
electronic. PPS: I have some decisions, but don't want to spoil
the question.  share|improve this qu