How FM radio works

So, question 3) is, how the hell does an FM radio even work? We tune our radio onto a specific "channel", i.e. specific frequency. Let's say we listen to some Bumfuck County Radio that broadcasts on 90 MHz. But the receiver actually doesn't listen to whatever's going on these 90 MHz, it listens to whatever happens around that frequency, right? The signal itself is not on carrier, it's on sidebands. So the frequency we tune our radio to actually has no meaningful info in it, it's just a reference point? Instead of listening what's oscillating at 90 MHz, it listens what happens at, say, 85-90 and 90-95, and converts that into audio?

Sorry if all that sounds very self-evident and I just seem to be a complete retard. That's because I am in terms of natural sciences, but I've at least resolved to do something about it, if only for a bit of self-respect.

social """science"""

>>9031113
I know, right. Too late to change the major, though.

>>9031094
The trick is that, depending on your country, the channels are around 50kHz appart.
This difference is more than enough to modulate sounds that can be picked up by human ears.
Geographically neighbouring stations are usually kept a few hundred kHz appart to reduce bleed.

>>9031126
So by government standards, some frequencies are deliberately kept empty so that channels don't overlap? I see!

>>9031131
Yep. That is why you need a licence to broadcast.
Otherwise some pirate radio station might screw with neighbouring channels, or in worse cases fuck with channels that are intended to be used by the emergency services and such.

>>9031138
Makes sense!

I also went to listen to some online radio using sites like http://websdr.ewi.utwente.nl:8901/ , and there they have a thing called spectrogram (?) instead of usual tuning scale. Most of it is dark blue, I guess that would be them empty channels, and in more or less even intervals, there're bursts of lighter stuff which is actual broadcast.

What I also noticed is that, say, when I tune that thing into 1000 kHz, there's nothing in that exact frequency. 1000 kHz itself is still dark blue. But all the music and whatnot is on the left and right of it. So I guess that means that our radios indeed don't listen to whatever freq we tune into, but near it! That's just fascinating.

(Insert neanderthal staring at fire image here)

>>9031145
>So I guess that means that our radios indeed don't listen to whatever freq we tune into, but near it!

In case of FM radio more like the intended frequence plus a standardized number of kHz above and below.
A FM channel is a clearly defined frequency range asigned to be used by their respective station.
It would be just a mouthfull to ask your audience to tune in between 90.425 MHz and 90.475 Mhz.

AM is a horse of another color, since it actually only needs one specific frequency to work.

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>>9031192
Yeah, guess it's easy to remember one number than a whole range of them! And yeah, I get it what you mean with "clearly defined range": took this screenshot from that site I've been using to nerd out about radio. Four visible columns of yellow stuff would be four separate radio stations, with the blue dark stuff inbetween being that assigned clear zone to prevent mixing, right?

...Now if only I could clearly understand how a normal audio wave is modulated into an FM wave and back again... If I am to look at that screenshot, I guess the audio wave containing music would be the vertical sine-looking wave plotted on top of the fuzzy yellow stuff (painted by yours truly in MSPaint with an acid green line)?

>>9031207
Now you can go listen to ayyy lmaos and post your findings on /x/, social """science""" faggot.

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>>9031225
I'm sorry sir, I think you spilled some.

>>9031093
I'm an engineer and I have no idea how radios work. I think EEs are the only ones who study stuff like this.

>>9031207
>I guess the audio wave containing music would be the vertical sine-looking wave plotted on top of the fuzzy yellow stuff

You guessed right.

You'll find plenty of literature and vids on YT that explain how exactly a FM modulator/demodulator works.

>>9031236
Aaaand that's what I came here to learn! Thanks for your patience and understanding of this
>social """science""" faggot
, kind anon!

>>9031235
Probably, but I'm just curious and knowing how stuff works is cooler than not knowing, I think!

>>9031093

>>9031094

Physics major but had an EE minor course on this once I'll try to answer;

What do you mean when you say 'a modulater which smushes the carrier wave into higher freq etc."?

1) What kind of answer do you want? Do you ask how a modulater actually works. Do you know about frequency space, btw? Looking at images in frequency space is way easier than describing it.

You didnt number the next question. anyway;
It is important to understand that, in practise, the amplitude and the frequency of a signal are completely unrelated (they're 'independent') . The frequency says how long it takes before the EM sine wave has reached the same phase again. For example, how long it takes to go from one maximum to the next maximum. A change in the size of the maximum (the amplitude) does not change this amount of time.

2) You are quite correct. The AM carrier signal has a bandwith but the frequency deviation is not added. This higher bandwith does result in a higher quality of sound btw. FM also has other cons such as less noise, less interference etc.

3) Imagine that the entire world is filled with a huge amount of electromagnetic waves at every single point in space (cosmic bckground radiation already accounts for 420 waves per cubic centimetres). In order to only pick up the ones youre interested in, the radio shifts all electromagnetic with a certain frequency (in the same way that a carrier signal shifts frequencies). The radio then only converts the signals that lay in a certain range, into an audible sound. You can imagine that shifting all waves with a different frequency, makes sure that you tune in to a different radio station.


You dont sound 'completely retarted' but obviously, studying sciences/engineering teaches you to phrase sentences in a certain style using certain jargon which is clear and efficient, but it takes long to grasp that and it's unique to every field so that doesnt help.

AM: song(t)*sin(freq*t)
PM: sin(freq*t + song(t))
FM: sin(freq*t + ∫song(t)dt)

>>9031792
> Do you ask how a modulater actually works?
Yeah, kinda. I want to have an understanding on how a usual audio wave (like a song) is turned into a modulated high frequency signal that doesn't sound like anything human ear can recognize, and how that signal if unfolded back into audible music in the receiver. Without highly specific details like what electronic parts I need to use, etc.

I mean, we have, say, some music, which is a wave in audible range with its own amplitude and frequency. And somehow that single wave turns into a wide stretch of different and extremely high frequencies that occupy much larger part of the spectrum. And everything the original wave had - its amplitutde, frequency, etc. - is encoded only in frequency difference? How the hell do you take three different characteristics of a wave and squish it into just one, that's just fascinating to me! The amount of brain (that I obviously lack) that the inventors must've put into it is astounding.

> Do you know about frequency space, btw?
Probably?.. As you said later, I may not know its proper name or any of that special jargon, I'm just a moron who've been taught useless crap for years who wants to not be completely stupid when it comes to how everyday tech works.