What is the waveform of radio frequencies? I thought they were sinusoidal; am I wrong?

I started to wonder about radio frequency waves at the time (two years ago), if they were digital, because all systems are digital, but the problem was that radios were being used in World Wars I and II, and even before. At that time, electronic devices were analog. So it can only be a sine but again, how can it be a sine wave when I know that electricity in my home is AC?

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    \$\begingroup\$ Yes - in the sense that ultimately everything is made of sinusoids? \$\endgroup\$
    – pjc50
    Dec 15, 2020 at 14:11
  • \$\begingroup\$ Maybe I think fourier series is helpful to you. Yes. they are made by sinusoidal maybe. but not sinusoidal all \$\endgroup\$
    – RNN master
    Dec 15, 2020 at 14:29
  • \$\begingroup\$ First, what do you mean with Radio Frequencies? an unmodulated signal? a modulated signal? if so, what kind of modulation do you mean AM, FM, PM? Do you mean a waveform in air or an electrical signal? a pure sine RF electrical signal is no different from a low frequency one, aside from frequency of course, in space it is a whole different matter, it depends on how the E and H fields are polarized. \$\endgroup\$
    – S.s.
    Dec 15, 2020 at 14:34
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    \$\begingroup\$ @autodidact If radio waves were pure sinewaves they wouldn't carry any information. No, they are not pulses either - you need to read up on modulation. \$\endgroup\$
    – Andy aka
    Dec 15, 2020 at 14:34

1 Answer 1


A modulated radio signal generally has a bandwidth which is a tiny fraction of its centre frequency. This means that any short stretch of signal will look essentially sinusoidal.

It's only when you look at longer stretches of signal, comparable to 1/bandwidth, that you start to see the effect modulation has on the signal. Amplitude modulation will alter its amplitude from moment to moment, phase modulation will alter its phase, and quadrature amplitude modulation will do both. But still, any sufficiently short stretch will still look sinusoidal.

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    \$\begingroup\$ "It's only when you look at stretches of signal "? \$\endgroup\$
    – user140351
    Jan 29, 2023 at 17:56
  • \$\begingroup\$ @autodidact Added punctuation to my answer in the hope that it will help, meaning 4 in this dictionary definition \$\endgroup\$
    – Neil_UK
    Jan 29, 2023 at 21:05
  • \$\begingroup\$ i was expecting a sample answer that i can understand i know by now that the waveform of RF is sinusoidal, and a signal is two waves one is the carrier and the second is the message. The first one has a higher frequency than the second. The carrier shaped with the message. \$\endgroup\$
    – user140351
    Jan 30, 2023 at 21:45

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