# spectrum of rectangle

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#### harry456

##### Member level 1
What is the formula of the spectrum of a rectangular signal, it should be some sort of sinc-function but according to my formula book it's something like u(t)=AT*sinc(piTf), but what's the formula that describes the signal that can be measured i.e. the ons-sided voltage spectrum? thx

#### onmyphd

##### Newbie level 4
I am not sure I get your question:
If you have a rectangular signal, the sinc function is the spectrum of the signal (you just need to take the positive frequencies and double the amplitude for the one-sided spectrum).
If your rectangle is a filter (like a sample and hold circuit), your input signal spectrum must be multiplied by the sinc spectrum to get the output voltage spectrum.

#### pebe

##### Advanced Member level 4
Harry,

Do you mean a square wave signal?

Does 'the ons-sided voltage spectrum' mean a voltage that swings from, say, 0V to 5V?

#### harry456

##### Member level 1
It's a rectangular wave with û=1V according to my maths formulary collection the ampl is A*T*si(pi*f*tau) but it's not possible to measure so. like [Volt*second]

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