# Draw Amplitude and Phase Spectrum for given signal

The above problem was asked in my class test. I understand that this waveform has a hidden symmetry.

x(t) = Square wave with p-p A + (A/10)

So, I can write fourier series expansion for it. As square wave contains odd half wave symmetry, so only odd harmonics of sin are present.

x(t) = sum[(2A/npi)sinnwt] + (A/10)

I am stuck here. How can I draw amplitude and phase spectrum from here?

A plot will be really helpful to understand.

• Is it truly a 50% duty square wave - it doesn't look that way how it has been drawn. – Andy aka Jan 30 '18 at 11:56
• T/2 and T is labelled in the diagram. – Nikhil Kashyap Jan 30 '18 at 12:02
• Then what is this hidden symmetry that you mention. Think about what I'm saying. – Andy aka Jan 30 '18 at 12:17
• hidden symmetry refers to square wave with dc offset. My instructor used a special name for such waveforms in class. – Nikhil Kashyap Jan 30 '18 at 13:01
• is that graph to scale, or is that middle crossing at T/2 ? – Jasen Jan 30 '18 at 19:37