I understand the basics of electromagnetic radiation and how transmitters emit information to receivers using carrier waves and specific modulations. (At least I think I understand).
What I don’t understand is how information–a person’s voice, a news broadcast, music, etc.–is encoded into a wave so that it can be transmitted in the first place. The HowStuffWorks and How Do Things Work websites don’t really answer this question and I decided to tap ya’lls brains. Someone please help me. This question has been keeping me up every night this week!
If you understand how signals are transmitted via carriers, you’ve done a good bit already. Hopefully you see your question applies to the situation when you don’t even send it through some other means – for example, I speak into a microphone which is connected to an amplifier and out comes sound through a speaker.
Knowing that may help you find the answer to your question, as you don’t need to search for anything related to radio itself. Or were you wondering exactly how the signal wave is combined into the carrier? (In short, what sort of ‘encoding’ are you talking about)
A simplified explanation, starting with the microphone. Sounds produced by my throat are air pressure waves. They strike a membrane of some sort (this is in the microphone) and vibrate it – now you have a mechanical wave. The membrane sits in an magnetic field which, when disturbed, generates a voltage wave to match.
So now you’ve got your signal as a voltage wave. Transmission depends on what method you use. If you’re sending it as an analog signal – in AM (at least AM radio ) the peaks of the carrier wave match the pattern of the voltage wave. In FM, the voltage wave is converted to a ‘frequency wave’, i.e. a varying frequency of the carrier.
If you wanted to send it digitally, you convert the voltage wave to digital values by picking whatever discrete voltage it’s closest to at a particular time. Then you send it as before using whatever method (AM or FM), only this time you’re only switching between two (normally) values.
Well you need to be able to accept that even sound travels as a wave and that complex sounds can be represented as a single complex wave with various different patterns of troughs and peaks. I guess that encoding a radio wave is just a matter of converting the complex soundwave pattern into a complex radio wave pattern, ie. from a format your brain can understand to a format another radio can understand. You say you understand about specific modulations so I won’t go into AM and FM.
This has probably been to basic an answer, some specific questions might help me refine it a bit.
Amplitude Modulation (AM) and Frequency Modulation (FM)
AM pysically increases the amplitude or power of the radio wave by essentially overlayng the voice frequency over the radio wave (gross simplification). The reciever filters out the the RF, again leaving just the voice frequency (crudely speaking).
FM is a little more complex… Voice frequency is used to change the base carrier wave frequency up or down a little bit. At the reciever, the RF is amplified and rectified, and the output is picked off as a voltage level, the value of which is dependant on the frequency of the recieved RF: Low (relatively speaking) freq==low voltage, high freq==high voltage. This voltage level will vary with the rate of the originally voice freq.
Digital can be carried over FM pretty easily also: High freq==high voltage==‘1’, low freq==low volts==‘0’.
AM could carry digital, but it would be more sloppy, and isn’t worth the trouble, generally speaking.
If you have a laser with precise control, you can switch it on and off at extremely high frequencies - 50kHz to a megahertz is nothing. You then apply FM or PCM modulation techniques to that “carrier.”
You can also stack carrier frequencies as well as modulation techniques, so a single fiber can carry dozens or even hundreds of channels, each of which is carrying two to four or more modulation channels. That’s how you get to gigabit speeds, not by pushing one channel insanely fast, but by stacking a whole bunch of very fast channels.
Here’s a websitewith a simple diagram showing how it works for AM radio, which is easier for lay people to understand.
An low frequency electrical signal from a mic is combined with a high frequency carrier signal. This is represented in the upper signal in this graph (FM is shown in the lower).
At the receiver side, the carrier signal is subtracted out of the signal and you are left with the same signal which you would have gotten from the mic.
This is of course, a gross simplification, but short of taking a few EE courses, it may do.
They’re called radio waves because they occupy the segment of the EMR spectrum designated as “radio,” which is a considerable ways from the segment even broadly designated as “light,” visible or otherwise.
Yes, they’re all EMR waves. But they’re neither all light nor radio (nor x-ray, nor gamma…)
It looks like Monstro (OP) is still with us. Do you understand it now?
If not, let me 'splain. On the sending end, sound is combined with radio and transmitted. On the receiving end, sound is separated from radio and sent to speakers. Got that?
What, in your esteemed opinion, are the frequency boundaries of “radio waves” and what properties do they have that distinguish them from “light waves?”
The range that’s broadly considered “light” is the range from radio waves through gamma rays. Visible light, of course, is a much narrower range, but it’s all light.
