Radio waves?

Question

I know I'm going to sound like an idiot for asking this, but school never really explained it. (at least not well.) I know that when a DJ speaks through a microphone in a radio station, radio waves are sent through the air to cars, radios . . . etc. Sometimes they travel great distances. But sound is vibrations and they slowly die out the further they travel, and being sent through radio waves is traveling. So my question is, how does the sound (or vibrations) of the DJ's voice make it all the way to our speakers before they die out?

Answer 1

In the case of sound waves the information (the music) is stored in compressions and rarefactions of the air traveling out from the source. Sounds waves lose energy quickly because they are attenuated, absorbed, and reflected by many things.



In the case of a radio station the information reaches your radio in the from of radio waves and then the radio converts the information in the radio waves into sound waves, which your ears can hear.



Radio waves travel much farther and better than sound waves because they do not get blocked, reflected, and absorbed by as many different things. Radio waves can also travel though a vacuum, sound wave can not. Radio waves pass through things like plastic, people and the walls of houses without being affected hardly at all. Most things are transparent or "invisible" to radio waves.

Answer 2

To add to Eri's comments... The radio waves are broadcast (transmitted by an antenna) at a specific frequency so, if you tune your radio to a different frequency, you tune in a different station. Different frequencies and wavelengths behave differently. AM/FM signals are mostly line of sight so, if you drive through a tunnel, you may lose reception. Short wave radios detect signals that bounce off the ionsphere so, if you have the right receiver, you can get radio signals from all around the world. Other radio signals go right through the ionsphere and out into space. This is how we communicate via cell phones with people across the country. This is also how we communicate with the Mars rovers and how we learn more about the universe. Radio waves are pretty cool.

Answer 3

The radio station generates extremely stable waves in the radio frequency range. This range permits more power to be generated & contained in the waves than do sound waves, so the signal goes a long distance. We can create a radio wave generator with power to send signals to the edge of the solar system. Also, radio waves are a very-much higher frequency than is sound.

The radio (receiver) to which you listen has a circuit which tunes itself (with your help in selection) to the signal broadcast at the radio station. When your receiver's circuit is exactly tuned to the broadcast signal the sound which comes out of the speakers is absolutely nothing - no sound. They are in harmony and so, the sound doesn't exist, is not produced.

Then, the broadcast station messes with the broadcast signal on purpose. The variation exactly matches the much slower, lower frequency modulations that sound expresses, and sends these variations out on its signal. This requires very good and expensive equipment.

The receiver's circuitry does not change, and these modulations cannot be followed. They become irritations to the circuitry, and so it spits them out into an audio amplifier circuit, which drives the speaker/headphones.

The broadcast radio waves are called the "carrier wave" because they carry the information, but are not part of the information. The information (music, voices - even rap) is called the modulation wave, or a couple of other names, depending on what features are of focus.

AM radio is 'Amplification Modulation", where the audio signal increases/decreases the power output slightly to follow the sound. FM is Frequency Modulation, which tweaks the output frequency slightly to track the audio.

Answer 4

Sound waves require a medium (air, water,metal etc.) in which to travel (they cannot travel in a vacuum) and really are just energy transmitted by the medium through which they travel. They travel at the speed of sound (different for each different medium) which is about 620 mph in air. Radio waves are a form of electromagnetic radiation and are, strictly speaking, not simple waves. They are particles (photons, the same particles as visible light which is also part of the electromagnetic spectrum) that have an associated wave function so sometimes they behave as discrete particles and sometimes as waves (and occasionally as a bit of both). There are two fundamental differences, electromagnetic radiation can travel through a vacuum (i.e. the 'vacuum' of space) and they travel at the speed of light which is approximately 186,000mile per second.

Answer 5

The sounds waves are converted to radio waves. Radio waves are light waves, not sound waves, so they will go on forever until they are absorbed. But as you get further away from the source, they drop off as a factor of 1 over the distance squared, so that's why you can't detect them from very far away very well.

Answer 6

You are getting good answers, but let me give you a view from another angle.

The RF frequencies, let's say on the range from 300KHz to 300MHz travel long distances. If at the radio-station they "modulate" (superimpose the sound frequencies, 20Hz to 20,000Hz), this low frequencies would be carried with the high frequencies. At the receiver end, the circuit would filter out the high f and let the low f get to the speaker.