# How do Radio Waves work when used for FM or AM Radio transmission?

• DCLawrence00
In summary, radio waves used for FM or AM radio have the sound encoded and riding on a carrier radio wave. This encoding is done through either amplitude modulation (AM) or frequency modulation (FM). In both cases, the signal is not a fixed pure frequency but a superposition of frequencies on either side of the carrier frequency. The width of an AM channel is 10 kHz and for FM it is 0.2 MHz. The modulation scheme determines the extra frequencies in the signal. The bandwidth used in most countries for FM is up to 75 kHz on either side of the carrier. The basic principle of information storage in a signal is that more variations in time lead to a wider frequency band.
DCLawrence00
I would like to know about radio waves used for FM or AM radio. I have read many articles that say, "The sound is encoded and rides on a carrier radio wave". How is that encoded? I am under the assumption that waves just have a frequency and wavelength and that is all. If a wave is transmitted at 101 Mhz then isn't that wave just a continuous 101Mhz? How does anything get encoded onto a wave of continuous frequency? Aren't wavelength and frequency locked together so that neither can be modified without modifying the other? If that's that the case, how can anything be "encoded"?

FM is a different, you can do your own search for that.

AM = Amplitude Modulation

FM = Frequency Modulation

DCLawrence00 said:
How does anything get encoded onto a wave of continuous frequency?

In both AM and FM, the signal is not a fixed, pure frequency. The signal is a superposition of the carrier frequency (the one that is indicated by your AM/FM tuner) and a range of frequencies on either side. The total width of an AM "channel" in the US is 10 kHz, including guard bands between channels. FM channels are 0.2 MHz wide, again including guard bands.

In AM, the "extra" frequencies are basically a byproduct of the modulation scheme. In FM, the "extra" frequencies are the fundamental nature of the modulation scheme.

Thanks jtbell. Simple, clear and to the point. So many things I read refused to just say it.

One way to look at the difference in AM and FM is that with an AM signal the modulation is in the power (Amplitude) of the carrier wave where in FM the modulation is in the frequency. On broadcast FM, I might be off , but I believe the bandwidth used in most countries it is up to 75 kHz on either side of the carrier depending on level of audio on the signal.

There is one common misunderstanding about frequencies:

Pure frequency applicable only for infinite constant wave.

Otherwise, even if there is a pure sinusoid for some interval, signal still has a frequency band, which width inverse to the packet size.

This is a basic principle of information storage in the signal: More signal variations in time lead to wider frequency band.

http://en.wikipedia.org/wiki/Fourier_transformation

## 1. How do radio waves carry information?

Radio waves carry information through changes in their frequency, amplitude, or phase. In FM radio, the amplitude of the wave remains constant while the frequency is varied to encode the audio signal. In AM radio, the amplitude of the wave is varied to encode the audio signal.

## 2. How are radio waves generated?

Radio waves are generated by an electronic oscillator, which creates an alternating current that is then amplified and transmitted through an antenna. The frequency of the oscillator determines the frequency of the radio wave.

## 3. How do radio waves travel through the air?

Radio waves travel through the air in a straight line at the speed of light. They are also able to reflect and diffract off of objects, which allows them to reach receivers in different locations.

An FM radio receiver contains a circuit that is tuned to a specific frequency, allowing it to receive the radio waves transmitted by the station. The receiver then converts the changes in frequency into an electrical signal, which is then amplified and played through a speaker.

## 5. Can radio waves be disrupted or blocked?

Radio waves can be disrupted or blocked by physical barriers, such as buildings or mountains. Interference from other electronic devices or signals can also disrupt the reception of radio waves. Additionally, changes in atmospheric conditions can affect the propagation of radio waves.

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