modulation explained, with demonstrations of FM and AM.

let's see what happens when I shine my torch on to my solar panel a question that's often asked is how is information transmitted from one place to another so for example if you turn on the radio you're getting information that's been transmitted via radio waves if you listen to your phone answering phone calls and speaking to a friend then again you're getting information via in this case microwaves and of course information can also be sent via optical fiber so in the form of light now all of those are forms of electromagnetic radiation but somehow information is encoded on them now what is that well in essence it is a term called modulation and that's what the subject of this video is all about but before I go on and explain modulation I want to demonstrate it as well now what I have here is a little box that's got a solar panel here and also a speaker and currently it's not producing any sound because it's receiving light fairly evenly in my other hand I have a phone and I have a torch and the phone and the torch are connected so the information from the music that is playing is encoded in the light you can't see it but we can actually pick it up we could transmit it at the speed of light onto my solar panel [Music] [Laughter] [Music] well maybe some of you know that song but what isn't happening here is is that the information is encoded on my light waves in other words it's modulated and this device here is extracting that information and we say it's demodulated so what is modulation well stay tuned let's find out [Music] so now that you've seen a little bit of a demonstration how I got the sound that is the signal from my phone on to the light that information was able to be processed to therefore get some sort of sound out of my speakers in essence what's happening is is that the information is somehow impressed on a carrier wave now in the example I showed you just a second ago the carrier wave was light or the visible light part of the spectrum and in some way I was able to put information onto that visible light spectrum all those visible light frequencies and what was able to be occurring was I was able to transfer that information on and then the small box was able to remove that information off so really this to private number of processors going on here and in essence what this is is called its modulation so adding that information onto the carrier wave is called modulation and then removing or extracting that information to be therefore transmitted to the speakers it's called demodulation now today I'm going to be discussing only the analog versions of modulation that is in specific we're going to deal with amplitude modulation and frequency modulation now there's also phase modulation which I'm not going to discuss and then there's also digital modulation which is a whole section again and not part of this video this is really about the basics of modulation so what does modulation actually look like so what I have here is an oscilloscope that's receiving signals from two sources I have amplifier one and amplifier two here and at the moment they're both putting out 500 Hertz and that's why these two wave patterns are exactly the same and so what we have here is the distance between them here represents the period and so therefore if I change the frequency we're going to see a change in the pattern so if for example if I have a lower frequency that means also my period is going to be longer I'm gonna show that because on the top I have the left side and the bottom I have the right side and I'm going to make the right side not 500 Hertz but 50 Hertz so straightaway you can see here that the period is longer so the frequency is lower and of course it is 50 Hertz if I were to measure the distances between the peaks the distances here would be ten times that one at the top now the first thing what I do is I want to show you what modulation is not so what I'm going to do is I'm going to add those two waves that is what we refer to as superposition and I could simply do this by my box over here and I'm going to change that section to adding and now what you see is we have the information down the bottom as a single object I'm and it seems to be superimposed on the top and you can see that the frequency of my carrier wave is still the same but the whole thing is going up and down and as a result you can actually see two sets of waves in there there is the obviously the wave that we had initially and then we also have the fact that we have this period of these two peaks which matches what we have here in the bottom now that is not amplitude modulation so what I will do now is I want to show you what amplitude modulation actually looks like so I can again change the settings here to do amplitude modulation and now what you'll see is is that we still we don't have a wavy line in a sense of going up and down we still have a wave but the amplitude is changed if you look carefully here we have the amplitude is a maximum and that corresponds to the peak of this signal here where we have a trough or let's say the bottom end of our wave there we have a amplitude that is weaker so what we have here is a changing of the amplitude that carries the information of the signal down the bottom if I were to change the frequency of the bottom wave and we're going to do it by simply multiplying this by two so we're going to go to 100 Hertz you can see now that the period differences of the original signal is still the same but the amplitudes actually now fluctuate at a greater rate and again it still matches the signal over here so this is what roofers are as amplitude modulation now this I will say is a very basic signal it's a single frequency so the sounds that you hear from the radio the sounds of any sorts of more complex sources are going to be a much more complex wave pattern here but nonetheless the wave pattern is such that the amplitudes in the carrier wave will match the patterns that are below it or in this case what our signal is he let's overlay the two so we can clearly see how the two are related so you can clearly see that the carrier wave changes in amplitude and matches the original signal that we applied to it now of course our source wave has a period and a frequency and by association the wave length and of course we can determine that on the modulated wave but of course our source wave also has an amplitude now there is a limitation here with this box that if I change the amplitude of my source signal it won't accurately represent what the modulated signal does so what I want to do is show you an animation that shows you also how changing our source signal amplitude changes the modulated wave so here you see three waves in this particular animation the red wave is of course our signal or a source wave the blue one is our carrier wave and then we have our modulated wave down the bottom and I'm going to change the frequency in this case here of my carrier wave and you can see the modulated wave matches that similarly if I change the frequency of my signal or my source wave you can see that also changes the modulated wave the point I want to make here though is how amplitude of the source wave changes the modulated wave now the first thing you'll notice is that if I change the size of my amplitude you will see that the maximum peak of my modulated wave gets larger and smaller but the other thing you should notice is that the peak of the minimum also changes so in low amplitudes the difference between the maximum and the minimum amplitudes is smaller so if I have a larger amplitude of my saw signal you can see the maximum amplitude is a lot bigger but the minimum amplitude is a lot smaller and so we have a greater difference between the minimum and the maximum amplitude as the amplitude of the original source wave increases and so that's how the modulated wave encodes the amplitude of our source wave so as a quick summary we have a signal here a modulator takes that signal and uses it to change the amplitude of the carrier wave so that the changes in the amplitude match the pattern of the wave and so of course at the other end if you receive that signal you can then have a demodulator which is able to extract that information to give us back our original wave and so therefore it's an easy way of transmitting information like our music with the light and of course also like and listening to your AM radio but now let's examine frequency modulation so again I'm going to return this back to 50 Hertz and we have this pattern but now I'm going to shift this to frequency modulation now what you notice now is that the amplitude of my carrier wave does not fluctuate at all it stays constant but if you look very carefully is that the pattern of frequencies or the periods we could talk about as well changes in respect to the wave down the bottom so if you look here at the peak here is that the frequency is actually a little higher there whereas at the bottom of this section here you'll find that the frequency is a little lower so you can see a repetitive pattern that matches the pattern down the bottom and what is happening is the frequencies change of frequency is modulated and so if I now change the frequency of my source signal let's say a hundred Hertz let's see what happens to our frequency pattern so now you can see more clearly that the pattern is not the bottom pattern now similarly in terms of frequency modulation the amplitude is also encoded in the wave form so you can get both the amplitude and the period which therefore by association allows us also to work out the wavelength of our source signal now I hope that helped you understand the basics of modulation in particular obviously amplitude modulation and frequency modulation now of course modulation is far more complex than that now I've alluded to that the fact that there are many different types of modulation and that's obviously a much deeper topic to explore maybe it's a chance for another video but certainly it's at a greater complexity and this video really is meant to be as an introduction to modulation now if you're a science teacher or a really enthusiastic student of physics you may be wondering where you can get the technologies that I used of course the first one was the light modulator with Associated torch and the second is our signal generator over here now I'm gonna put a description in below you can investigate that yourself I do actually recommend the light modulator it actually has some great demonstrations not only modulation but other demonstrations as well and I've used it a fair bit in the classroom well I hope that this helped you understand the basics of modulation please like share and subscribe put a comment down below if this has been particularly useful to you and of course if you're a regular follower of my channel maybe consider supporting me via patreon to help me continue to produce physics videos to a high school level my name is Paul from high school physics explained take care bye for now

Channel: PhysicsHigh

Views: 15,027

Keywords: what is modulation, frequency modulation explained, amplitude modulation explained, am modulation explained, fm modulation explained, radio modulation explained, modulation basics, modulation fm, modulation frequency, modulation radio waves, frequency modulation, amplitude modulation, fm modulation, am vs fm, what is modulation in physics, am vs fm radio waves, amplitude modulation and frequency modulation, analog modulation vs digital modulation

Id: XnoHXyb7dkY

Length: 12min 22sec (742 seconds)

Published: Thu Jun 18 2020