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What is the meaning of spectrum in simple words?

Is it just "range or set of different frequencies "

Just like fm spectrum is between 88MHZ to 108MHZ?

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  • $\begingroup$ Please, in questions, display your own research. In this case, there's multiple pretty good articles e.g. on wikipedia that you could have consulted, and based your "I've read this and that, but in this one passage, they say that XYZ, but XYZ contradicts my understanding, so: what about ABC?" precise question. What you did here, instead, is asking for us to copy out an encyclopedia article for you. Also, notice that "simple words" depends on the reader, and we don't know what you think is simpl.e $\endgroup$ – Marcus Müller Mar 22 at 9:13
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The word spectrum does NOT mean "a range of frequencies". Stated differently, the word spectrum does not mean "a frequency range". The word spectrum means "a description (a portrayal) of how much energy exists in a signal at all the different frequencies within some frequency range". That description could be a two-column table with one column listing the individual frequencies within a frequency range and a second column listing how much energy a signal contains at each of the frequencies listed in the first column. We might call that two-column table a "tabular spectrum".

A far more common description of how much energy exists in a signal at all the different frequencies within some frequency range is a two-dimensional "graphical spectrum". That is, a two-dimensional drawing of a curve where the horizontal axis is frequency (covering some frequency range) and the vertical axis is a measure of energy. As such the vertical position of a point on the curve at some frequency indicates how much energy a signal contains at that frequency. This "graphical spectrum", the curve, I've just described is simply called the "spectrum" of a signal.

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I think the term spectrum in signal processing came from 'colour spectra' (https://en.wikipedia.org/wiki/Spectral_color) where in distant objects were used to determine whether they were moving away or towards earth. Not really sure of it though. So if you see the wiki link, there are different frequencies (or wavelengths) assigned to each colour band. Basically these are electromagnetic frequencies in the visible light band. So in simple words, yes, spectrum is a range or set of different frequencies. When you say you want to view the spectrum of a signal, you are referring to see how signal is composed of various frequencies.

Broadly, it may mean collection of similar objects. See https://www.merriam-webster.com/dictionary/spectrum

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