# How to find period of signal, when spectrum is known?

Here is signal in frequency domain .Division of frequencies does not give an integer number or real number. May it can be here another method of finding period for ths signal.

• Is your question about one signal, or two signals? I see two different spectrums in the figure. – MBaz Nov 19 '18 at 23:18
• Is it a given that the deltas correspond to periodic sinusoids? That is not necessarily the case in general. Also: are you interested in finding one period, or the fundamental period? The latter is much harder to find in general. And finally: see this answer: math.stackexchange.com/a/164238/204966 – MBaz Nov 19 '18 at 23:36
• @MBaz , the one on the right is almost equivalent to the spectrum on the left. but $\sqrt{150}$ should be $\sqrt{147}$ and then they would be equivalent. – robert bristow-johnson Nov 20 '18 at 2:32
• @robertbristow-johnson I agree :) – MBaz Nov 20 '18 at 2:49

Division of frequencies does not give an integer number or real number.

• real number: any two real numbers (aside from 0) divided give a real number, so that claim is wrong. Also, doesn't matter.
• integer: not a relevant property here.

You should probably look into the definition of rational numbers. And hint: Divide your frequency axes by $$\sqrt{3}$$. That doesn't change the ratio of numbers, but makes things easier to see.

(also, I'm not even saying there is a period for both your signals.)

• Division of $\sqrt{3}$ remains the ration of numbers, but how to proof or disproof that this singnals are not periodic? – Conversion Nov 19 '18 at 23:20
• That's a new question, but as said, look into the defnition of rational numbers. Combine that with the knowledge about the period of the individual components from the spectral plots. – Marcus Müller Nov 20 '18 at 0:46
• But what is the knowledge about period of the individual components from the spectral plots? – Conversion Nov 20 '18 at 1:26
• lesseee... 5, 7, and 10 are all multiples of what? – robert bristow-johnson Nov 20 '18 at 2:33