Define the Characteristics of Radio Frequency (RF)

0:05Welcome to define the characteristics of Radio Frequency, or RF. And, furthermore, welcome to the CWNA course. We are going to dive into the world of wireless. And the CWNA is a great way to do that, whether you have experience in the industry already as a network engineer or whether you're just getting started but you're being told that, hey, you're going to be doing some wireless or whatever the situation is. I use that as an example because that's exactly what happened to me in the industry. When I got started, I was not really familiar with a whole lot of networking.

0:36And so they handed me a CWNA book and said, here, Jeff, you're going to study this. And you're going to do wireless networking. And so one of my very first experiences in this industry was with CWNA. Now, I did a wireless networking for a long time before moving into other areas of the networking world. And so wireless always has had a very special place in my heart. I absolutely love wireless. I just continue to find myself being pulled back into the wireless world. And the CWNA training that we're about to embark on is going to be a big part of that.

1:09So, again, whether you're-- or regardless of where you are in your journey, again, I really believe the CWNA is a great place to be because we're going to explore, not only things from a wireless perspective, but we're going to be introducing some networking concepts in here as well. And so, if you have that foundation, then fantastic. But if you don't, then you're going to get the pieces that you need in order to be a good wireless engineer. So as far as this skill is concerned, we're going to start with this whole idea of RF. What exactly is radio frequency? The name radio might actually be a little bit of a misnomer to us.

1:42Because, when I think about radio, I'm thinking of a radio app or, hey, an old-school radio actually pulling radio waves out of the air. And so I think of it as being audio. But radio waves are actually light. And so we're going to talk about the physics of light waves. Because, ultimately, when we're talking about Wi-Fi, whether it's coming from an access point or, for that matter, mobile signals and TV over the airwaves, all of these are just a different form of light. It's just light that we can't see. And that's the key here.

2:13So as soon as we understand that, it's going to really set us up with a strong foundation for talking about a lot of other characteristics and properties of light waves. Because, if we're going to understand things like interference and multiple pathing and all kinds of other just even the way that we do modulation with our waveforms, we need to understand what a waveform even is. So this skill is all about laying a very strong foundation for establishing us as having a good understanding of what wireless is, RF specifically, what RF signals are, how they propagate in space.

2:45And, from there, we can start to kind of erect our knowledge right on top of that foundation. So we're going to have a lot of fun exploring the physical properties of light waves. This is I always enjoy this part of the training. So we're going to have a lot of fun doing this. I will see you in the next video.

0:05As promised, let's go ahead and jump into the physics of light conversation. We're going to explore what exactly we mean by the physics of light waves. I mean, what are we talking about here? Is light really waves, because I've heard light can be particles, we probably all heard of photons, and whether it's in sci-fi or actually studying a science textbook, photons are real. And so it's just a matter of parsing through all this information and figuring out, number 1, what exactly light is, but then also how is that going to affect us in studying Wi-Fi So let's go and jump in and have ourselves a physics lesson.

0:38So why in the world are we talking about the physics of light? Well, as mentioned, when we have a Wi-Fi device, it's going to be sending out signals that we often refer to as RF signals where RF stands for Radio Frequency. If we didn't know any better, we might think of this as something like sound or pressure wave, something along those lines. As mentioned, the fact that it stands for Radio Frequency, the word radio to a lot of us means something to do with audio here. But that's just not the reality. It's not sound waves. It's not any kind of pressure waves. Instead, it is actually light waves that we're talking about.

1:10Well, what's interesting about this is when we look at it from a human eye perspective, I'm actually sitting here looking at this wireless device, I don't see any of these light waves coming out. And that's just further reason for why we might not recognize them for what they actually are. And the fact is that this light cannot be seen by the human eye in the same way that maybe in science class you did an experiment where you were listening to different frequencies and they have a whole range of sound frequencies. And so they tuned it really, really low and all of a sudden you couldn't hear anything.

1:43And then they turn it up, and you can start to hear this faint beep and it gets higher and higher pitch. And eventually, it also disappears. Well, that's because there's a bunch of sound waves that have really high frequencies we can't hear and a bunch of sound waves with low frequencies that we can't hear, and light is the exact same way. We have this visible spectrum in the middle that we can see and we have frequencies that are lower and higher than the visible spectrum that we cannot see. And so we're going to be talking a little bit about the electromagnetic spectrum in the next video.

2:14But for now, just understand that what we're talking about is light waves that we can't see. So effectively, these wireless devices, they're actually blinking at each other. It's kind of a weird way of thinking about it. But they're blinking at each other with different frequencies in ways that they can understand it. So in the same way that maybe a we're across the lake from one another, it's late, we can't really see each other, but I could shine a red light or a green light at you, in fact, that's how boats communicate with one another, to be able to tell, hey, are you going the same direction as me or are you coming at me, depending on which the green on the left or is the red on the left.

2:49But either way, I could send you a signal by using different colored lights. And that's exactly what we're talking about when it comes to access points and wireless devices, is they're using different frequencies and really ultimately different waveforms to communicate digital information like bits and bytes. And so that's exactly what we're going to expect out of our wireless communicators here. So one question we need to ask ourselves a little bit is what exactly is light? Because we often talk about it as if it's a wave, but it actually has a dual nature.

3:20So you may have heard of this concept called the wave particle duality. I know when I was in college, we had to learn all about the wave particle duality nature of light, because it changes the way light behaves depending on really how you're experimenting on it. And so what it means is that sometimes light behaves as a wave and sometimes it behaves as a particle. And back in the late 1800s, early 1900s with some really smart people working on this stuff. Einstein is a name that a lot of people know. We also had Maxwell Planck, and we had Niels Bohr.

3:53And so there's a whole lot of these really smart scientists who did a whole lot of experimentation to figure out what exactly light was. And there are two famous experiments that were run, the first of which was called the double slit experiment. And so if you remember, back when we maybe studied this in middle or high school science, we have this concept of having a single slit, if we had a single slit, then light would actually make it through all right, and that's fine. But if light was a particle, it would also be able to make it through. Well, when you insert a second slit into this wall, so now we've got two separate holes and now you actually shine light race through this.

4:32Well, now what it creates is it creates this effect where we start to see where these light waves are interfering with one another. And so you get this strange effect where it's bright in some places and dark and other places. And if light was a particle, just going through these holes like this, then it wouldn't actually do that. And so this experiment shows that light behaves like a wave. And so we could imagine the same thing, just with water here, if we're looking down on a lake and we had water waves going at a wall in the water, so some kind of dam that's building up the water, but we have these slits in the wall, then we'd expect the waves to look like this.

5:09And so this is how we can relate it back to how light is behaving as well. Well, this is well and good. We could say that, all right, light definitely behaves like a wave except we had another very famous experiment called the photoelectric effect. And the photoelectric effect essentially is saying that light has to get absorbed in discrete quantities. And so as we shine light down on an electric, well, really a metallic surface and we're studying the electric currents that it produces, what we find is that if this was operating purely as a wave, then this is an analog concept.

5:43And so I should be able to absorb however much energy that I'm pushing down onto this photoelectric plate. But what was found is that the energy that's absorbed is actually more of a digital nature, meaning that, basically, what we've got is we do have light behaving like particles here, where light gets absorbed one particle at a time. And Einstein originally called these quanta. However, he eventually renamed it to the concept of a photon. And so we hear this word sometimes in science fiction, but we actually can also refer to it in real science because it's a real thing.

6:17Now, this is really fun, at least I think it's really fun how light behaves like this. However, it's not actually going to affect us as wireless engineers at least as far as light operating as a particle. Instead, we care more about this concept, the fact that light behaves like waves. And we'll see a lot more of this here later on in the skill. Now, one other thing to consider in all of this is the concept of the speed of light. The speed of light has been established by science to be a constant, and that constant is usually represented by a letter c, a lower case c.

6:48And so c, the speed of light has been measured out to be about 2.99 times 10 to the 8 meters per second. And we use the speed of light in a lot of different physics equations and math equations. In fact, you may know of a famous one that is E is equal to Mc squared. This is an equation that Einstein came up with. It's called the theory of relativity, and it's basically saying that energy is equal to the mass times the speed of light squared. So that c stands for the speed of light. And again, we've basically got this down as far as the speed of light in a vacuum, meaning that there isn't anything in between the source of the light and when we measure it.

7:28However, as soon as we start to shine light through water or yes, even through the air, well, this is going to start to slow down. However, for the most part, within the framework of a Wi-Fi W especially even outside, the distances aren't great enough that we can expect a large variance in the speed of light. So any of our calculations, we can pretty well take the speed of light to be this 2.99 times 10 to the 8 meters per second. So how fast is 2.99 times 10 to the 8 meters per second? It's hard for us to grasp some of this at times.

8:01And so one of the best ways we can think of it is when the sun is shining light on our planet here, so here's the Earth, we are receiving that light, believe it or not, 8 minutes after the sun sent it. And so in a weird way, we're actually looking back in time when we look at the sun and we're observing it, hopefully not with our eyes directly. But when we're observing the sun, we're seeing what the sun looked like minutes ago. And so the joke is always, hey, the sun could have exploded five minutes ago and we wouldn't know actually because we're still waiting for the light to catch up to us and to show us at the sun exploded.

8:35But hopefully, we'd get some warning signs before the sun exploded, I suppose. Either way, then we extrapolate that out and we say, all right, so now here's the Earth and really the solar system. So here's our sun when the Earth is nearby, and now we're looking at the closest star to our solar system. And this is about 93 million miles away or 150 million kilometers away, and it's a star by the name of Alpha Centauri, just technically a triple star system. But either way, the amount of time that it takes for light to get back to Earth for us to see this star is over 4 years.

9:10It's about 4.35 years, is what it takes. And so this is the concept of a light year. We say, OK, Alpha Centauri is 4.35 light years away. So when we say light year, we're not actually talking about a measurement of time. We're talking about a measurement of distance. It's how far a light can travel in a year. And so if it takes 4.35 years to get from Alpha Centauri to the Earth, then Alpha Centauri is 4.35 light years away. So one of the key takeaways that we need to understand is that Wi-Fi is going to communicate using these radio frequency waves.

9:45And so we're talking about light waves, is ultimately what we're saying. And so when we think about the properties of light, a lot of times that's what we can apply to RF. If light reflects off of a surface and we know it's very reflective because it's metal or maybe it's a mirror, then we can expect our Wi-Fi signal to also bounce off of that same surface because it shares the same characteristics. Now, light has a constant speed in a vacuum. So in the vacuum of space, we'd expect it to be really close to this 2.99 times 10 to the 8 meters per second.

10:15However, the purpose of us talking about that is to understand that these communications signals, they're not instant. They don't just instantly appear on the other side of the room or on the other side of whatever it is we are sending our signal across. And so, yeah, when I flip the light switch on, it appears that the light immediately comes on to me because I can't perceive how fast light is traveling, especially in an enclosed space like this. But when we really slow everything down, this is going to be really important as we consider things like multi-pathing and understanding that wireless signal is traversing space and maybe bouncing off of different surfaces.

10:50Well, it's because it's traveling at just about the speed of light. I mean, air doesn't slow it down that much. And so understanding that it has this constant speed helps us to understand the behaviors of these different waveforms. Now in wireless networking, again, we studied this or we talked about the wave particle duality, kind of a cool thing. But ultimately, when we're talking about what we're doing with Wi-Fi signal, it tends to be a little bit closer to the double slit experiment. So what we're saying is that we're not trying to excite things.

11:20It doesn't have anything to do with the amount of energy or absorbing them and distinct quanta like these photons. It really is more about how do waveforms behave and how can we manipulate those waveforms to convey more information and maybe create this beam-forming path. And if we can combine signals, we can maybe direct it out a certain way. And so the more we understand that RF signals operate like light waves, the more we're going to be able to take advantage of that and really bolster our technology, but also our understanding of how to deploy this technology.

11:50I know this has been informative for you, and I'd like to thank you for viewing.

0:05Now that we understand that RF signals are really just light waves, it's time for us to take a look at what these waveforms actually are. As we explore more and more within the world of wireless communications, we're going to find that we're doing a lot of manipulations around these individual waveforms. So we're going to talk about those manipulations and the things that we're going to do with them. Well, first of all, we need to understand what exactly they are. So Let's dive in and take a look. All right, let's talk about waveforms. The primary waveform we're going to be talking about is what we call a sign or a sinusoidal waveform.

0:36And it looks something like this. And this is to be contrasted with, for example, a square wave which looks kind of similar but with all of these angles. And there's all kinds of different waveforms out there. The sinusoidal waveform is really characterized by these curves. So we curve up and over, we curve down and back up, and we repeat this over and over again. And so a waveform might look something like this, where we continue this pattern up and down. So when we look at this waveform, we need to understand the different components of the waveform.

1:06For example, up here at the top, we have what's called the crest. And we have a lot of crests. We have a crest basically every cycle. So we have over here, we have over here. And then on the other side of the waveform, we have what's called the trough. And I know, thanks to English, this is a wonderful way to spell trough, but it is what it is. And it's the bottom of the sinusoidal waveform. So we have a trough over here, we have a trough over here. And then cutting right down through the middle is what we call the origin. And so the origin is basically our reset point.

1:38And so when we are looking at the origin, what we should expect to see is that the same distance exists between the origin and the crest, as what it exists between the origin and the trough. In fact, there's a special name for this distance, and this is called the amplitude. And so this is probably one of the first terms that we're going to find that we use quite a bit. If we, for example, we have the same type of sinusoidal wave pattern, other than that it doesn't go nearly as far, well, this is going to be, maybe, a lower amplitude version of the same waveform.

2:09So for the sake of clarity, let's just go ahead and get rid of that from our drawing. Now, we have a couple of other important concepts here, we have what's called the period. The period is the amount of time, and so that's what's key here, it's the amount of time that it takes for one of these cycles to pass by. And so we can measure from any point on the waveform, as long as we measure to the exact same spot on the waveform at the end of the cycle. So naturally we might say that truly the start of the cycle where it crosses the origin to when it crosses the origin going in the same direction, going back up.

2:40And so the amount of time this takes, maybe it's, I don't know, making up a number here, 30 milliseconds. That would be the period for this waveform. But keep in mind that it can also measure from let's say right here. Now we're going back down where we hit the crest, we're going back down, and I can then measure to the next time this happens. So the next time we hit the crest, we're going back down. And so right here. And so if I measure the amount of time between those two points, it should also be 30 milliseconds because the period doesn't matter where we measure, as long as we measure from one point to the same point at the end of the cycle.

3:16Now lastly, we have the concept of phase. Phase is interesting because we kind of need to compare a waveform to another waveform in order to understand phase, because it's a relative concept. So right now we have a phase that we might call zero degrees here. And then we're going to have another waveform that is going to look very much the same, other than it's lagging behind just a little bit as we see. And so this waveform is just out of phase, we like to say, with the first waveform that we drew.

3:47And the distance between, let's say, where the trough is for the one waveform and the trough is for the next waveform, this distance right here is going to define our phase. And just like having the zero degree waveform as the original one that we were comparing to, we're going to measure this in degrees. And so we might say that our green wave is 45 degrees out of phase with the original waveform. Now, importantly, if I were to draw a waveform that is exactly opposite-- I'm using a different color here just to make things a little bit more clear.

4:17If it's exactly opposite the yellow waveform where we're always crossing origin at the same point, just going backwards, and where our trough line up with our crests, what we're going to find is that this is 180 degrees out of phase. And this concept of phase is going to matter a whole lot when we talk about interference later on in this skill. All right, so let's go and clear off our drawing here and talk about the concept of frequency. Frequency is a huge part of any Wi-Fi communications conversation. And you probably are familiar with this already, and just from the idea of a 2.4 gigahertz network versus a 5 gigahertz network.

4:52Anytime we're talking about the concept of Hertz, that's a frequency conversation. So what we have here when we're talking about frequency is frequency is really asking us to measure the number of cycles per second. And that's an interesting way of saying it because ultimately this concept of cycles doesn't have a unit of measurement. This isn't something like distance over time like meters per second would be. Instead, it's just something divided by seconds. And so really what we're talking about here is a one over second type of way of measuring this.

5:26And so this measurement, this unit of measurement, one over second, this is the concept of a Hertz. Now, Hertz is not a plural form of the word hurt, OK. This is named after a scientist named Heinrich Hertz, and so we're talking about a last name. And so this is why we always capitalize the H in Hertz. It's just like we typically like to do if we have a unit of measurement that's named after somebody. And so we're going to abbreviate this as capital H and then a lowercase z.

5:58And so what we're going to now look at here is, OK, well, what do different frequencies represent? So if I were to say that this entire wavelength occurs over one second, we can count how many cycles there were. So I see one cycle here, and then I see a second cycle here, and then I see most of a third cycle. So maybe we'd say, like, it's close to three. I'm just going to count that as being done. So let's say that this in one second we got three different cycles. So the frequency of this waveform is going to be 3 Hertz, because it's how many cycles per second.

6:36And so as we start to ramp up the frequency, we're going to see that we get a whole lot more cycles in there. For example, I could draw a waveform in here that is roughly twice as fast. And so if I were to squeeze in, for example-- wait, let me just make sure I'm doing this right. Yeah. So now I've got two waveforms in here. I know the amplitude got a little funny there, let's do that again. There we go. So I got two waveforms in here, two waveforms and another two waveforms. I know it's not the prettiest. But ultimately what we're saying here is I've got, 1, 2, 3, 4, 5, 6 different waveforms, so now I'm at 6 Hertz.

7:14So I just doubled the number of cycles that are on this waveform within the exact same time period. And so I can get faster and faster and faster. And so I could get to the point where I have 1,000 cycles, and so that would be 1,000 Hertz. And we can abbreviate that. We can say that this is actually one kilohertz because the cake for kilo is representative of the fact that it's 1,000. And so if I have 2000, I would have two kilohertz, if I have 1,000 thousands, well now we're talking about a million, and that would be a megahertz.

7:49So one-- let's just try that out with six zeros, one million Hertz is going to be megahertz. And then same thing. We can do a billion and say now we've got one with nine zeros after it, that would be 1,000 millions, so that's a billion. And that would be one gigahertz. And so when we're talking about Wi-Fi occurring in the 2.4 gigahertz and 5 gigahertz space, this is what we're talking about. We're talking about how many cycles there are per second.

8:20And gigahertz is in the billions, if we can believe that. And truly billions of these waveforms happening or these cycles happening within a single second of time. And so this is what we're talking about when it comes to light and frequency. Now, just for the fun of it, I like to compare our Wi-Fi signals to visible light, because we're very familiar with visible light. And so we've got red and we've got-- well, really, it's just the ROYGBV concept. Red, orange, yellow, green, blue and violet.

8:52And I believe we got rid of indigo at some point. When I was young there was an I in there but we'll just leave it as ROYGBV. All that to say when we're talking about the visible light spectrum, this ranges from, believe it or not, 400 terahertz on the red end, that's the low end. And we go up to 800 terahertz here on the high end where we have violet light. And so when we talk about a terahertz, well, a terahertz is just like in the world of computer data.

9:22A terabyte is 1,000 gigabytes, so a terahertz is 1,000 gigahertz. And so ultimately when we're comparing, for example, 5 gigahertz of Wi-Fi, which is on the higher end of our frequency spectrum, we can actually do have six gigahertz now, but we're comparing 5 gigahertz in Wi-Fi to truly 400,000 gigahertz as the low end of our visible light spectrum. And so this is shows the comparison of how much lower frequency our Wi-Fi is relative to the visible light spectrum.

9:56All right, let's wipe out the chalkboard and talk about one last concept which is important, which is the wavelength. The wavelength of a waveform is sort of like the period, in that I'm going to take any point on the waveforms, let's just say right here in the middle and close to origin. And we'll measure to that same spot at the end of the cycle. But rather than measuring the amount of time that it takes, we're going to measure the actual physical distance. And so typically when we're talking about wavelength, we're measuring this in terms of meters. Now, sometimes that's literal meters, sometimes it's larger than meters.

10:28We could be talking about kilometers. But a lot of times we're talking about something smaller, something more in the range of millimeters or micrometers, or even nanometers and picometers. And so just depends on how much frequency we have, because wavelength is actually going to be tied in parallel here a little bit to the concept of frequency. So what do we mean by comparing wavelength and frequency? Well, they're going to be inversely proportional to another. Because if we think about it, if I'm going to increase the frequency, then that means I'm going to take this waveform and I'm going to get two separate cycles within the same amount of time that would have taken for us to do one cycle.

11:07Well, if I'm measuring now from this part to this part, we'll, compare that line to this line down here. We just see that we shrunk that line roughly in half. Because we squeezed our waveforms together, so we could fit more in there, so now we've got two times the frequency. However, now our wavelength has actually trunk in half. And so that's why they're inversely proportional to another. Now the other thing to consider is the fact that since we're measuring physical distance here and we're talking about so many cycles per second, we've got a one over second here.

11:40But we can actually relate this back to the speed of the waveform, because speed is going to be some amount of distance divided by some amount of time. So if we have a frequency and we want to know the wavelength, we can do that so long as we understand what the speed is. Well, this is why it's important we have that conversation already. We know what the speed of this waveform is. The speed of this waveform is going to be the speed of light, that constant C that we talked about. So the equation to compare wavelength and frequency is simply that the speed of light is equal to the wavelength, which we represent with the Greek letter Lambda, times the frequency, which we usually use a cursive f for.

12:18And so it just sort of a curvy f I suppose, if you want to call it that. But ultimately, if I've got the frequency of something-- so remember what we said about it being 3 Hertz earlier. But I've got 3 Hertz for the frequency, and I know what the speed of light is, it's that 2.99 times 10 to the eighth meters per second. Well, now I can calculate out the wavelength. I can do my quick algebra here and say wavelength is equal to the speed of light divided by the frequency. And what's interesting here is that we can basically round this to three, and that's because that's exactly what we have here, is three Hertz.

12:50So we'd say that this is equal to-- just, again, we're estimating, 3 times 10 to the eighth, divided by 3. So the 3's are going to cancel out. And so we're left with 10 to the eighth meters. Now 10 to the eighth just means that we have 10 zeros, so we're talking about hundred and then three zeros here and 3 zeros here. So that would be 1,000, million, 100 million meters. And so that's a very, very long wavelength. I mean, I don't think that we can really understand just how big of a wavelength that is.

13:21And so if truly we set an RF wave to behave, to operate at 3 Hertz, the size of our wavelength is going to be enormous. But as you can imagine, as we start to increase the frequency of that light wave, well, then this wavelength is going to start to drastically shrink. Now, just like before, I like to compare this to the visible light spectrum to get an idea of what we're talking about here. Because on the Wi-Fi side of things, we've got a wavelength of about six centimeters, this would be four 5 gigahertz Wi-Fi.

13:52If I take this equation and I replace my 3 Hertz with 5 gigahertz, which, again, is 5 billion Hertz, well, now that wavelength is going to get a whole lot smaller, and it's all the way down to six centimeters. Which is still something that I can see. I mean, I can look at my hand and estimate what six centimeters might be. And so this here is Wi-Fi. However, when I think about visible, light visible light is operating much higher frequencies. Remember we talked about 400 terahertz and 800 terahertz. And so visible light is actually going to range between 400 and 700 nanometers.

14:27Nanometers is one billionth of a meter. And so these are teeny, teeny, tiny, far smaller than the naked eye could ever perceive. And so we're talking about six centimeters all the way down to the nanometer scale, that is much, much smaller. And so sometimes it's telling to see just what we're talking about when it comes to the reds and blues that we can see, versus what exactly these access points and these wireless devices are using to communicate with one another. So when we think about the anatomy of waveforms, we do need to understand concepts such as the crests and the troughs and where the origin is and the amplitude.

15:00Amplitudes is going to be a big one, as well as phase. But then we also need to think about frequency and wavelength. So we'll start with frequency here. It's the measurement of the amount of cycles over time, and we use the unit of measurement called the Hertz in order to measure that. So if I can count three seconds or three cycles within a second, that tells me that I'm operating at 3 Hertz. And so when we look at something like Wi-Fi operating in the billions of Hertz, that tells us how many cycles are happening within just a single second. Now, likewise we need to consider wavelength.

15:32And wavelength is inversely proportional to frequency, meaning a frequency increases, wavelength will always decrease. And at the same value, relative value. So frequency doubles, wavelength halves. If frequency triples, then wavelength is divided by three. And we see why we've got this relative to the speed of light. It's just like basically how we do math when it comes to these sinusoidal waveforms. Now, wavelength is the length of a cycle in actual physical distance. And so even though we can't see light waves and we can't necessarily measure them with a measuring stick, we can run the calculations, like we talked about, to figure out how exactly long those wavelengths are.

16:12I hope this has been informative for you, and I'd like to thank you for viewing.

0:05Well, as it turns out, our light waves can behave at pretty much any frequency. We're talking about really, really low frequencies like my 3 hertz example to really, really high frequencies. But we're not just talking about gigahertz and terahertz. We're talking about much, much greater frequencies. So when look at small frequencies to very large frequencies, this forms what we call the electromagnetic spectrum. In this video, we want to take a look and see what exactly the spectrum is, where on the spectrum our Wi-Fi falls, and then start to understand how it all ties together. Let's take a look. As humans, we are actually able to tell what frequency light is behaving at because different frequencies of light turn into different colors for us, and so even the yellow of my pen that I'm using right now is a different frequency than, let's say, the blue of this text up here, and our eyes are able to distinguish that so long as our eyes are working like they're supposed to.

0:54And so oftentimes what we can compare this to specifically is the rainbow, and I already mentioned the colors of the rainbow before. We had red, orange, yellow, green, blue-- sometimes we throw indigo in there-- and then violet. And we see this specific range of colors, especially when we look at, for example, a rainbow in the sky and we see all of these different colors lined up with one another. Well, that's because of the frequency of light. And so what we're really saying is that red is the lowest frequency of light and violet is the highest frequency of light, where orange lies somewhere in the middle.

1:30But orange is less than yellow, and yellow is less than green and so on and so forth. And so it's pretty fascinating how we can interpret different frequencies as different colors. But even more fascinating is the fact that there are just a ton of frequencies that we cannot see, and those would be frequencies that are lower than red and frequencies that are higher than red. And so we have to be really cognizant, I suppose, of the fact that the electromagnetic spectrum is so much bigger than we can perceive with our human eye.

2:02And so it's lovely to look up into the sky and see these beautiful rainbows, but there's a whole lot of other colors that we just can't see. And so when we talk about these colors-- or maybe I should call them frequencies-- what we find is that we can go as very, very low as we want down to, again, a single hertz, 1 hertz, 2 hertz, 3 hertz. And then we can go higher than what we can see, so even starting with terahertz and going to petahertz, for example, and exahertz. And we can go all the way up to, let's say, something times 10 to the 18th or times 10 to the 20th hertz, and we're talking about an enormous number of cycles per second.

2:39And because this is a spectrum, we tend to break this down into what we call regions, and so I'm just going to throw some barriers up here and understand that when we're talking about a particular region we're talking about a range of frequencies that our signals would be classified as. And so we can start right away by talking about the regions directly outside of red and violet. And we have special names for those, and you've probably heard of them. We have the infrared region, and we have the ultraviolet region. Now, infra, if we look at the English word there, what exactly is that saying?

3:12Infra means below, and so infrared has always been talking about the fact that it is the frequency region below red light. Likewise, ultra-- we talk about ultra. Some superheroes seem like they have ultra in their name. It means above. It means high. It means-- maybe we like to think of it as powerful, but ultimately it's the opposite of infra. Infra means below. Ultra means above. And so we're talking about ultraviolet. This ultraviolet region means that it has a higher frequency than violet.

3:45And so these are the first two regions that we tend to talk about a little bit because we're concerned about UV rays. We need to be careful with that because they can give us sunburn and some even worse health effects as a result of being exposed to high levels of frequency, these radiation types. And so as we look higher than ultraviolet, we get into the X-ray domain, and X-rays-- a lot of us are probably familiar with those just from the medical world perspective.

4:15I know I can go into the hospital. I can get an X-ray of my broken hand. It'll show me all of my bones. But really what they're doing is they're shining X-rays through my hand against a photoelectric plate that's essentially going to capture an image of what's happening inside of my hand. And so that's why we have to use X-rays for that. But again, this is like UV. It's very, very high frequency, and so we've got to be careful with this. It has very negative health effects, which is why hospitals are tracking how many X-rays we have.

4:45And the attendant who manages the X-ray-- they have to run behind a shield because if they're exposed to X-rays constantly that would be very dangerous. And then we have gamma rays up here. Yes, if you follow comic books you probably have heard of gamma rays, but that's the comic book version of it. There are real-life gamma rays. We don't have any practical uses for it that I'm aware of. I'm sure there's something out there for these, but ultimately, gamma rays are just anything above X-rays. So it just kind of keeps going and going.

5:15And so now we look at something-- at the frequencies lower than infrared, and the biggest one is right-- whoops, I started spelling the wrong one. The biggest one is the microwave region, and so, yes, this is where our microwaves that we use in our kitchens operate. And that's one good. Other than-- we can possibly think of something more applicable to the course, which is Wi-Fi. This is where we fly lives. It lives at a much lower frequency even than infrared, let alone visible light. And so when we talk about the health implications of Wi-Fi, the reason why science says that Wi-Fi radiation is safe is because not only is it below the frequency of some of these dangerous rays like ultraviolet and X-rays, it's actually lower than the frequencies of visible light.

6:02And so we're not just talking light from the sun because that has ultraviolet light in it, but we're talking about just the colors that are reflecting off of my walls having much, much higher frequency, we just said, 400,000 hertz or 400,000 gigahertz, rather, versus the 5 gigahertz that my Wi-Fi is operating at. And so when we talk about the wavelengths-- the wavelength is like 6 centimeters. That's a pretty large wavelength. And so we're not as concerned about Wi-Fi signal causing damage in the same way that UV and X-rays-- they can actually jump into our cells and destroy parts of our cells.

6:43So from a health perspective, that's why we say it's safe. It's the same reason why we say using microwaves in our kitchen-- that it's safe for using on food because all it's doing is heating up the water. It's not actually injecting radiation into our food. It's in the same way that shining a flashlight on our food wouldn't actually cause our food to have problems. And so the last region down here-- this is what we call radio waves. The reason why it's called radio waves is because we use these for broadcasting radio and TV.

7:16And so especially back before streaming services and when we have an antenna outside of our house and we're receiving signals for our radio-- in fact, we still use this in our cars extensively when we're tuning into the radio, et cetera. That's where we're getting our signals from. And so they operate in the radio space. But again, as I mentioned earlier, I think some people hear radio waves and assume this has to do with audio. It has nothing to do with audio. It can convert into a data, and so that data can be a picture like on our TV.

7:49It can be audio like the TV audio. It can be audio like our radios. But ultimately, it's doing exactly what Wi-Fi does, which is encoding information into these different waveforms. And it's operating at such a low frequency that, number one, it's very, very safe, but also, number two, it can go really, really far much, much further than any of the waveforms that are in a higher part of the spectrum. And so that's the other part we want to talk about here is how frequency relates to our distance because as we might imagine, it doesn't do me much good if my house where I've got my TV antenna up here, let's say-- so I'm not sure how to draw this TV antenna.

8:32There we go, some kind of Yagi antenna. And I need to be as close to the TV station with a big antenna on it or what have you. I need to be this close to the TV station just to get that signal in the same way that need to be right next to an access point to get Wi-Fi signal. Now, instead, we want this to be miles or many, many kilometers away. In fact, we need this to be sometimes in adjacent cities, and so this is why the lower frequency is used, because the lower the frequency, the greater the distance that signal can propagate using the same energy levels.

9:07And so this is why, if I step out of my house and I just take a few steps away sometimes, my Wi-Fi doesn't quite make it out of my house to my outdoor area. Now, I might see my neighbors' Wi-Fi or something along those lines, but oftentimes the quality is very, very low. And certainly I'm not going to be able to get it miles away from my house, and so that's because we're using a much higher frequency. We're using that 2.4-gigahertz frequency or the 5 gigahertz or now the 6-gigahertz spectrum, and so these are much higher frequencies than my radio and TV waves are using.

9:41Now, this doesn't just affect our distance. It's also going to affect our propagation. When I say propagation, really I'm talking about through things. So we're talking about walls. We're talking about buildings, whatever it is that's impeding our path. And so once again, I might have a bunch of houses, or I might have a building here between the TV station and my house, and this signal is going to pass through just fine because of the lower frequency. And the same way that my Wi-Fi-- I might have my floor plan look something like this, where I've got a hallway here.

10:14And I've got the access point in the hallway, and I've got two rooms right next to this access point. Well, I'd expect that the access point is going to be able to communicate into these rooms. It can communicate through walls because it's a much lower frequency than all of these frequencies up here, even visible light. So this is one reason why visible light can't go through walls. However, visible light, we understand, can go through things that we might call translucent. Translucent means that I can get partial amounts of light through something. So maybe I think about a candle.

10:46If I shine a flashlight against a candle, I can see that light go through the candle. I can even see the flashlight go through my hand to some extent. Visible light is able to go through some materials. But certainly, as we get into UV and especially X-rays and gamma rays, it's much harder for those types of radiations to penetrate things. That's why we use lead vests when we're taking X-rays because it blocks those X-rays solid. It makes it so that they can't get through, whereas certainly a radio wave is going to be able to go through that same type of shield. So understanding that the higher the frequency we get the lower the distance that our propagation is going to go and the more that walls, and buildings, and obstacles are going to impede our communications.

11:28So when it comes to our key takeaways, one of them is simply going to be that it's really cool how our eyes can detect different frequencies of light by representing them to us as different colors. So when we're seeing blue versus red, we're truly seeing completely different frequencies. Red is as low of a frequency as we can see, and blue, especially violet, is as high of a frequency as we can see. So next, the electromagnetic spectrum we see is-- yeah, it's got the visible light right there in the middle, but it really goes very, very far, way higher and way lower on the spectrum.

12:00And so it's important that we can identify the different regions and especially understand that Wi-Fi communications, and cellular, mobile data, those kinds of things-- they all operate within the microwave part of that spectrum. Now, lastly, as we talked about, the higher the frequency goes, the less far that those waveforms are going to be able to propagate. So it's going to have more problems with obstacles. It's going to have problems even just in free space, just trying to get across things. But ultimately, this is why we use the lower frequencies for our communications, because we want our communications to be able to go certain distances.

12:37And so when we look at the applications, sure, TV and radio-- that might be coming from the next city over. It needs to be a very low frequency so that those waveforms-- remember how long those waveforms can get at the lower frequencies. They are going to have an easier time passing through obstacles, whereas then as we get into higher levels of radiation or higher levels of frequency, that's going to be harder and harder to do. I hope this has been informative for you, and I'd like to thank you for viewing.

0:05Well, we have reached the end of a skill. So let's take a moment to review what we've learned with a quiz. First up out of three questions, what letter is used to represent the speed of light in physics equations? And by the way, please hit the pause button and make sure that you have given yourself enough time to answer each one of these questions as we go through them. So the answer here is C. Remember that famous equation, E equals mc squared, where that C is representative of the speed of light. And the speed of light is a constant that we measure out to be roughly 2.99 times 10 to the eighth meters per second.

0:42Now, a lot of this specific knowledge isn't really required for being a wireless engineer. However, if we don't understand these basic physics concepts, it is going to impede our understanding of what's really happening when we talk about wireless communications. Next question, a wireless waveform has a frequency of 3 gigahertz. What is the wavelength? So remember our equation, the speed of light is equal to our wavelength, which is represented by that Greek letter Lambda, times the frequency.

1:12And so we know what the speed of light is. We understand that it's, in this case we'll call it, roughly 3 times 10 to the eighth. That'll make our math a little easier. And then we say equal to the wavelength times the frequency in this case, which would be 3 gigahertz. Now, 3 should be multiplied by 10 to some kind of power here. So what are we talking about? Well, kilohertz is equal to 10 to the third power. That would be 1,000. Megahertz would be a million, that's 6. Gigahertz is a billion, which is 9. Those would be 3 times 10 to the ninth.

1:44And so, at this point, it's just algebra. So we can say that wavelength is equal to the value of C, here, 3 times 10 to the eighth, divided by 3 times 10 to the ninth. And so this is going to make for some pretty easy math here. We cancel out the 3's. And 10 to the eighth divided by 10 to the ninth, this is going to result in 1 over 10. And so it's a tenth of a meter. Always remember that it's measured in meters. So this is 0.1 meters which we could call 10 centimeters if that's how we want to write it out.

2:14But ultimately, this is going to be our answer. So at this point, it's more about just understanding how we go about calculating it. We need to remember this equation right here and be able to do the math when we're asked to do so. OK. Last question, which type of electromagnetic radiation will have the shortest free space propagation? Let's remember the relationship that we defined here. If we increase the frequency of our light waves then we are going to find that we can't quite go as far, our distance is going to overall decrease, not just in free space, by the way, but also through objects in most cases.

2:50And so at this point, what we need to understand is how is the electromagnetic spectrum laid out. And so we've got the visible light right here in the middle. And from here, we recall, we've got infrared and ultraviolet. And so we can put those there. And then we've got x-rays and gamma rays. And then we have the microwaves and the radio waves. And so as we look at these various options, we see x-rays all the way over here. We see visible light is lower than the x-rays. And so that's not going to be an answer. Radio waves are all the way at the bottom, and microwaves are just right above it, which by the way, remember, this is where Wi-Fi exists, is inside of the microwave region.

3:26So when we compare all of these answers, x-rays would be the highest frequency on the electromagnetic spectrum. And so that is going to be our answer. So that wraps up our quiz. If you found that some of this information didn't quite propagate properly then be sure to go back and review the information that we discussed in order to get it all down. Otherwise, congratulations on completing Define the Characteristics of Radio Frequency. I hope this has been informative for you. And I'd like to thank you for viewing.