# How can a periodic signal (a wave) be able to transfer information?

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I know that the equation of armonic motion depends on three parameters: amplitude, frequency, phase. When a radio is receiving a signal from another radio, they’re on the same wavelength, that’s measured by period/frequency; so I guess that’s a “fixed” variable, or at least a variable that doesn’t carry information, but permits to choose which signal to listen to.

So how does a wave transfer information? Is it because the other two parameters change (or at least its amplitude).

In: Engineering

* There are many types of wave modulation.
* One type is amplitude modulation.
* That works, basically the way you’ve described.
* The amplitude of the wave is changed over time in a way that matches the changing amplitude of say..an audio signal.
* However another common type is Frequency Modulation.
* So in that case the radio receiver doesn’t lock onto a single frequency, but rather a small range or “band” of frequencies.
* In that case, the transmitter slightly modifies the frequency of the wave and those modifications are what convey the information.
* So if you wanted to transmit audio, you would make the frequency slightly lower than normal when the audio wave is negative, and you’d make the frequency slightly higher when the audio wave is positive.

There are two types of radio: AM (Amplitude Modulated) and FM (Frequency Modulated).

AM radio carries information by keeping a constant frequency, but varying the amplitude of the wave.

FM radio carries information by varying its frequency. The general audible range for humans tops out at about 20kHz (it depends a lot on things like age), so if you’ve got two FM signals that are set 1MHz apart, then both signals can vary by 20kHz without interfering with each other. You can “subtract” the constant 1MHz part of the signal out from the variance using electronics, which will leave you with just the original 0-20kHz signal.

You guessed it. The two main methods of transmitting data through a radio wave are amplitude modulation and frequency modulation (otherwise known as AM and FM radio).

In amplitude modulation the amplitude of the carrier wave (with a very high frequency) is changed in accordance another wave known as the signal wave (this has the frequency that you tune into). This carries a signal.

Arguably better, there is frequency modulation, where the amplitude and phase of the carrier wave remain constant, and instead the frequency of the carrier wave is changed with respect to the phase of the signal wave (for example when the signal wave is at a peak the frequency of the carrier wave is at its highest and when the signal wave is at a trough the frequency is much lower).

Hope this helps 🙂

For AM, it’s a series of Amplitude Modulation changes. For FM, it’s a series of Frequency Modulation changes, hence the naming conventions