Define the Characteristics of Radio Frequency (RF)

0:05Welcome to define the characteristics

0:07of Radio Frequency, or RF.

0:09And, furthermore, welcome to the CWNA course.

0:12We are going to dive into the world of wireless.

0:14And the CWNA is a great way to do

0:17that, whether you have experience in the industry

0:19already as a network engineer or whether you're just

0:22getting started but you're being told that, hey, you're

0:25going to be doing some wireless or whatever the situation is.

0:28I use that as an example because that's exactly what

0:30happened to me in the industry.

0:32When I got started, I was not really

0:34familiar with a whole lot of networking.

0:36And so they handed me a CWNA book and said,

0:39here, Jeff, you're going to study this.

0:41And you're going to do wireless networking.

0:43And so one of my very first experiences in this industry

0:48was with CWNA.

0:50Now, I did a wireless networking for a long time

0:52before moving into other areas of the networking world.

0:55And so wireless always has had a very special place in my heart.

0:58I absolutely love wireless.

1:00I just continue to find myself being pulled back

1:03into the wireless world.

1:04And the CWNA training that we're about to embark on

1:07is going to be a big part of that.

1:09So, again, whether you're-- or regardless of where you are

1:12in your journey, again, I really believe the CWNA is a great

1:16place to be because we're going to explore,

1:18not only things from a wireless perspective,

1:20but we're going to be introducing some networking

1:22concepts in here as well.

1:23And so, if you have that foundation, then fantastic.

1:26But if you don't, then you're going

1:27to get the pieces that you need in order

1:29to be a good wireless engineer.

1:32So as far as this skill is concerned,

1:34we're going to start with this whole idea of RF.

1:37What exactly is radio frequency?

1:39The name radio might actually be a little bit

1:41of a misnomer to us.

1:42Because, when I think about radio,

1:44I'm thinking of a radio app or, hey, an old-school radio

1:48actually pulling radio waves out of the air.

1:51And so I think of it as being audio.

1:53But radio waves are actually light.

1:56And so we're going to talk about the physics of light waves.

1:59Because, ultimately, when we're talking about Wi-Fi,

2:01whether it's coming from an access

2:02point or, for that matter, mobile signals and TV

2:06over the airwaves, all of these are just

2:08a different form of light.

2:10It's just light that we can't see.

2:12And that's the key here.

2:13So as soon as we understand that,

2:14it's going to really set us up with a strong foundation

2:17for talking about a lot of other characteristics

2:19and properties of light waves.

2:21Because, if we're going to understand things

2:23like interference and multiple pathing

2:25and all kinds of other just even the way

2:28that we do modulation with our waveforms,

2:30we need to understand what a waveform even is.

2:33So this skill is all about laying a very strong foundation

2:36for establishing us as having a good understanding of what

2:40wireless is, RF specifically, what RF signals are,

2:44how they propagate in space.

2:45And, from there, we can start to kind of erect our knowledge

2:49right on top of that foundation.

2:52So we're going to have a lot of fun

2:53exploring the physical properties of light waves.

2:56This is I always enjoy this part of the training.

2:58So we're going to have a lot of fun doing this.

3:00I will see you in the next video.

0:05As promised, let's go ahead and jump into the physics

0:08of light conversation.

0:09We're going to explore what exactly we mean

0:11by the physics of light waves.

0:13I mean, what are we talking about here?

0:15Is light really waves, because I've

0:17heard light can be particles, we probably all heard of photons,

0:20and whether it's in sci-fi or actually studying a science

0:24textbook, photons are real.

0:25And so it's just a matter of parsing through all

0:28this information and figuring out,

0:29number 1, what exactly light is, but then

0:32also how is that going to affect us in studying Wi-Fi So let's

0:35go and jump in and have ourselves a physics lesson.

0:38So why in the world are we talking

0:39about the physics of light?

0:41Well, as mentioned, when we have a Wi-Fi device,

0:43it's going to be sending out signals

0:45that we often refer to as RF signals where

0:48RF stands for Radio Frequency.

0:50If we didn't know any better, we might

0:51think of this as something like sound or pressure wave,

0:55something along those lines.

0:56As mentioned, the fact that it stands

0:58for Radio Frequency, the word radio to a lot of us

1:01means something to do with audio here.

1:03But that's just not the reality.

1:04It's not sound waves.

1:06It's not any kind of pressure waves.

1:07Instead, it is actually light waves that we're talking about.

1:10Well, what's interesting about this

1:12is when we look at it from a human eye perspective,

1:15I'm actually sitting here looking

1:16at this wireless device, I don't see

1:19any of these light waves coming out.

1:21And that's just further reason for why

1:23we might not recognize them for what they actually are.

1:26And the fact is that this light cannot be seen by the human eye

1:30in the same way that maybe in science class you did

1:33an experiment where you were listening to different

1:35frequencies and they have a whole range of sound

1:38frequencies.

1:38And so they tuned it really, really low

1:41and all of a sudden you couldn't hear anything.

1:43And then they turn it up, and you

1:45can start to hear this faint beep

1:46and it gets higher and higher pitch.

1:48And eventually, it also disappears.

1:50Well, that's because there's a bunch of sound waves

1:53that have really high frequencies we can't hear

1:55and a bunch of sound waves with low frequencies

1:58that we can't hear, and light is the exact same way.

2:00We have this visible spectrum in the middle that we can see

2:03and we have frequencies that are lower and higher than

2:07the visible spectrum that we cannot see.

2:09And so we're going to be talking a little bit

2:11about the electromagnetic spectrum in the next video.

2:14But for now, just understand that what we're talking about

2:16is light waves that we can't see.

2:18So effectively, these wireless devices,

2:20they're actually blinking at each other.

2:22It's kind of a weird way of thinking about it.

2:24But they're blinking at each other

2:26with different frequencies in ways

2:27that they can understand it.

2:28So in the same way that maybe a we're across the lake from one

2:34another, it's late, we can't really see each other,

2:36but I could shine a red light or a green light

2:38at you, in fact, that's how boats communicate with one

2:41another, to be able to tell, hey,

2:43are you going the same direction as me or are you coming at me,

2:45depending on which the green on the

2:48left or is the red on the left.

2:49But either way, I could send you a signal

2:51by using different colored lights.

2:53And that's exactly what we're talking

2:54about when it comes to access points and wireless devices,

2:58is they're using different frequencies and really

3:00ultimately different waveforms to communicate

3:02digital information like bits and bytes.

3:04And so that's exactly what we're going

3:06to expect out of our wireless communicators here.

3:09So one question we need to ask ourselves a little bit is

3:12what exactly is light?

3:15Because we often talk about it as if it's a wave,

3:18but it actually has a dual nature.

3:20So you may have heard of this concept called the wave

3:23particle duality.

3:24I know when I was in college, we had

3:26to learn all about the wave particle duality

3:28nature of light, because it changes

3:30the way light behaves depending on really

3:34how you're experimenting on it.

3:36And so what it means is that sometimes light

3:38behaves as a wave and sometimes it behaves as a particle.

3:41And back in the late 1800s, early 1900s

3:44with some really smart people working on this stuff.

3:47Einstein is a name that a lot of people know.

3:49We also had Maxwell Planck, and we had Niels Bohr.

3:53And so there's a whole lot of these really smart scientists

3:56who did a whole lot of experimentation

3:58to figure out what exactly light was.

4:00And there are two famous experiments that were run,

4:03the first of which was called the double slit experiment.

4:06And so if you remember, back when we maybe

4:08studied this in middle or high school science,

4:11we have this concept of having a single slit,

4:14if we had a single slit, then light

4:16would actually make it through all right, and that's fine.

4:19But if light was a particle, it would also

4:21be able to make it through.

4:22Well, when you insert a second slit into this wall,

4:26so now we've got two separate holes

4:28and now you actually shine light race through this.

4:32Well, now what it creates is it creates this effect where

4:35we start to see where these light waves are interfering

4:38with one another.

4:39And so you get this strange effect

4:41where it's bright in some places and dark and other places.

4:44And if light was a particle, just

4:45going through these holes like this,

4:48then it wouldn't actually do that.

4:50And so this experiment shows that light behaves like a wave.

4:54And so we could imagine the same thing, just with water here,

4:57if we're looking down on a lake and we

4:59had water waves going at a wall in the water,

5:02so some kind of dam that's building up the water,

5:05but we have these slits in the wall,

5:06then we'd expect the waves to look like this.

5:09And so this is how we can relate it

5:10back to how light is behaving as well.

5:13Well, this is well and good.

5:14We could say that, all right, light definitely

5:16behaves like a wave except we had

5:17another very famous experiment called

5:19the photoelectric effect.

5:21And the photoelectric effect essentially

5:24is saying that light has to get absorbed

5:27in discrete quantities.

5:29And so as we shine light down on an electric,

5:33well, really a metallic surface and we're

5:34studying the electric currents that it produces, what we find

5:38is that if this was operating purely as a wave, then

5:42this is an analog concept.

5:43And so I should be able to absorb however much energy

5:46that I'm pushing down onto this photoelectric plate.

5:49But what was found is that the energy that's absorbed

5:52is actually more of a digital nature,

5:54meaning that, basically, what we've got

5:57is we do have light behaving like particles here,

6:00where light gets absorbed one particle at a time.

6:03And Einstein originally called these quanta.

6:05However, he eventually renamed it to the concept of a photon.

6:09And so we hear this word sometimes in science fiction,

6:12but we actually can also refer to it in real science

6:16because it's a real thing.

6:17Now, this is really fun, at least

6:19I think it's really fun how light behaves like this.

6:21However, it's not actually going to affect us

6:23as wireless engineers at least as far

6:25as light operating as a particle.

6:28Instead, we care more about this concept, the fact

6:30that light behaves like waves.

6:32And we'll see a lot more of this here later on in the skill.

6:35Now, one other thing to consider in all of this

6:37is the concept of the speed of light.

6:40The speed of light has been established by science

6:43to be a constant, and that constant

6:45is usually represented by a letter c, a lower case c.

6:48And so c, the speed of light has been measured out

6:52to be about 2.99 times 10 to the 8 meters per second.

6:56And we use the speed of light in a lot of different physics

7:00equations and math equations.

7:01In fact, you may know of a famous one that

7:03is E is equal to Mc squared.

7:06This is an equation that Einstein came up with.

7:08It's called the theory of relativity,

7:11and it's basically saying that energy

7:12is equal to the mass times the speed of light squared.

7:15So that c stands for the speed of light.

7:17And again, we've basically got this down as

7:20far as the speed of light in a vacuum,

7:23meaning that there isn't anything

7:25in between the source of the light and when we measure it.

7:28However, as soon as we start to shine light

7:30through water or yes, even through the air, well,

7:34this is going to start to slow down.

7:36However, for the most part, within the framework

7:39of a Wi-Fi W especially even outside,

7:42the distances aren't great enough

7:44that we can expect a large variance in the speed of light.

7:47So any of our calculations, we can pretty well

7:49take the speed of light to be this 2.99 times 10

7:53to the 8 meters per second.

7:54So how fast is 2.99 times 10 to the 8 meters per second?

7:58It's hard for us to grasp some of this at times.

8:01And so one of the best ways we can think of it

8:03is when the sun is shining light on our planet

8:06here, so here's the Earth, we are receiving

8:09that light, believe it or not, 8 minutes after the sun sent it.

8:14And so in a weird way, we're actually looking back in time

8:17when we look at the sun and we're observing it, hopefully

8:19not with our eyes directly.

8:20But when we're observing the sun,

8:22we're seeing what the sun looked like minutes ago.

8:24And so the joke is always, hey, the sun

8:26could have exploded five minutes ago

8:28and we wouldn't know actually because we're still

8:30waiting for the light to catch up to us

8:32and to show us at the sun exploded.

8:35But hopefully, we'd get some warning signs before the sun

8:38exploded, I suppose.

8:39Either way, then we extrapolate that out

8:41and we say, all right, so now here's the Earth and really

8:44the solar system.

8:45So here's our sun when the Earth is nearby,

8:48and now we're looking at the closest

8:50star to our solar system.

8:52And this is about 93 million miles away

8:56or 150 million kilometers away, and it's

8:59a star by the name of Alpha Centauri,

9:01just technically a triple star system.

9:03But either way, the amount of time

9:05that it takes for light to get back to Earth for us to see

9:08this star is over 4 years.

9:10It's about 4.35 years, is what it takes.

9:14And so this is the concept of a light year.

9:15We say, OK, Alpha Centauri is 4.35 light years away.

9:20So when we say light year, we're not actually

9:22talking about a measurement of time.

9:24We're talking about a measurement of distance.

9:27It's how far a light can travel in a year.

9:30And so if it takes 4.35 years to get from Alpha Centauri

9:34to the Earth, then Alpha Centauri

9:35is 4.35 light years away.

9:38So one of the key takeaways that we need to understand

9:41is that Wi-Fi is going to communicate using these radio

9:43frequency waves.

9:45And so we're talking about light waves,

9:47is ultimately what we're saying.

9:49And so when we think about the properties

9:50of light, a lot of times that's what we can apply to RF.

9:54If light reflects off of a surface

9:56and we know it's very reflective because it's metal

9:58or maybe it's a mirror, then we can expect our Wi-Fi signal

10:02to also bounce off of that same surface

10:04because it shares the same characteristics.

10:06Now, light has a constant speed in a vacuum.

10:09So in the vacuum of space, we'd expect

10:10it to be really close to this 2.99 times 10

10:13to the 8 meters per second.

10:15However, the purpose of us talking about that

10:18is to understand that these communications signals,

10:21they're not instant.

10:22They don't just instantly appear on the other side of the room

10:26or on the other side of whatever it is we

10:28are sending our signal across.

10:29And so, yeah, when I flip the light switch on,

10:32it appears that the light immediately comes on to me

10:35because I can't perceive how fast light

10:36is traveling, especially in an enclosed space like this.

10:39But when we really slow everything down,

10:41this is going to be really important as we consider things

10:44like multi-pathing and understanding

10:45that wireless signal is traversing space

10:48and maybe bouncing off of different surfaces.

10:50Well, it's because it's traveling at just

10:53about the speed of light.

10:54I mean, air doesn't slow it down that much.

10:56And so understanding that it has this constant speed

10:59helps us to understand the behaviors

11:01of these different waveforms.

11:03Now in wireless networking, again, we studied this

11:06or we talked about the wave particle

11:07duality, kind of a cool thing.

11:09But ultimately, when we're talking

11:10about what we're doing with Wi-Fi signal,

11:14it tends to be a little bit closer

11:15to the double slit experiment.

11:17So what we're saying is that we're not

11:19trying to excite things.

11:20It doesn't have anything to do with the amount of energy

11:23or absorbing them and distinct quanta like these photons.

11:26It really is more about how do waveforms behave

11:29and how can we manipulate those waveforms to convey

11:33more information and maybe create this beam-forming path.

11:36And if we can combine signals, we

11:38can maybe direct it out a certain way.

11:40And so the more we understand that RF signals operate

11:43like light waves, the more we're going

11:44to be able to take advantage of that

11:46and really bolster our technology, but also

11:48our understanding of how to deploy this technology.

11:50I know this has been informative for you,

11:52and I'd like to thank you for viewing.

0:05Now that we understand that RF signals are really

0:07just light waves, it's time for us

0:09to take a look at what these waveforms actually are.

0:11As we explore more and more within the world

0:14of wireless communications, we're

0:16going to find that we're doing a lot of manipulations

0:19around these individual waveforms.

0:21So we're going to talk about those manipulations

0:23and the things that we're going to do with them.

0:25Well, first of all, we need to understand what exactly they

0:27are.

0:27So Let's dive in and take a look.

0:29All right, let's talk about waveforms.

0:31The primary waveform we're going to be talking about

0:33is what we call a sign or a sinusoidal waveform.

0:36And it looks something like this.

0:38And this is to be contrasted with,

0:40for example, a square wave which looks kind of similar

0:43but with all of these angles.

0:44And there's all kinds of different waveforms out there.

0:46The sinusoidal waveform is really

0:49characterized by these curves.

0:51So we curve up and over, we curve down and back up,

0:54and we repeat this over and over again.

0:56And so a waveform might look something

0:58like this, where we continue this pattern up and down.

1:02So when we look at this waveform,

1:03we need to understand the different components

1:05of the waveform.

1:06For example, up here at the top, we

1:08have what's called the crest.

1:09And we have a lot of crests.

1:11We have a crest basically every cycle.

1:14So we have over here, we have over here.

1:16And then on the other side of the waveform,

1:19we have what's called the trough.

1:21And I know, thanks to English, this is a wonderful way

1:23to spell trough, but it is what it is.

1:25And it's the bottom of the sinusoidal waveform.

1:28So we have a trough over here, we have a trough over here.

1:31And then cutting right down through the middle

1:33is what we call the origin.

1:35And so the origin is basically our reset point.

1:38And so when we are looking at the origin, what

1:40we should expect to see is that the same distance

1:43exists between the origin and the crest,

1:45as what it exists between the origin and the trough.

1:48In fact, there's a special name for this distance,

1:50and this is called the amplitude.

1:52And so this is probably one of the first terms

1:54that we're going to find that we use quite a bit.

1:57If we, for example, we have the same type of sinusoidal wave

2:00pattern, other than that it doesn't go nearly as far,

2:04well, this is going to be, maybe, a lower amplitude

2:08version of the same waveform.

2:09So for the sake of clarity, let's

2:11just go ahead and get rid of that from our drawing.

2:13Now, we have a couple of other important concepts

2:15here, we have what's called the period.

2:17The period is the amount of time,

2:19and so that's what's key here, it's the amount of time

2:21that it takes for one of these cycles to pass by.

2:24And so we can measure from any point on the waveform,

2:27as long as we measure to the exact same spot on the waveform

2:30at the end of the cycle.

2:32So naturally we might say that truly the start of the cycle

2:35where it crosses the origin to when

2:37it crosses the origin going in the same direction,

2:39going back up.

2:40And so the amount of time this takes,

2:42maybe it's, I don't know, making up a number here,

2:4430 milliseconds.

2:45That would be the period for this waveform.

2:47But keep in mind that it can also measure from let's say

2:50right here.

2:51Now we're going back down where we hit the crest,

2:53we're going back down, and I can then measure

2:56to the next time this happens.

2:58So the next time we hit the crest, we're going back down.

3:00And so right here.

3:02And so if I measure the amount of time between those two

3:06points, it should also be 30 milliseconds

3:09because the period doesn't matter where we measure,

3:11as long as we measure from one point

3:13to the same point at the end of the cycle.

3:16Now lastly, we have the concept of phase.

3:19Phase is interesting because we kind of

3:21need to compare a waveform to another waveform

3:23in order to understand phase, because it's

3:26a relative concept.

3:27So right now we have a phase that we

3:29might call zero degrees here.

3:31And then we're going to have another waveform that

3:35is going to look very much the same,

3:37other than it's lagging behind just a little bit as we see.

3:41And so this waveform is just out of phase,

3:44we like to say, with the first waveform that we drew.

3:47And the distance between, let's say,

3:49where the trough is for the one waveform

3:51and the trough is for the next waveform, this distance right

3:54here is going to define our phase.

3:56And just like having the zero degree waveform

3:58as the original one that we were comparing to,

4:01we're going to measure this in degrees.

4:03And so we might say that our green wave

4:05is 45 degrees out of phase with the original waveform.

4:09Now, importantly, if I were to draw a waveform that

4:12is exactly opposite--

4:14I'm using a different color here just

4:15to make things a little bit more clear.

4:17If it's exactly opposite the yellow waveform

4:20where we're always crossing origin at the same point,

4:22just going backwards, and where our trough line up

4:25with our crests, what we're going to find

4:27is that this is 180 degrees out of phase.

4:31And this concept of phase is going

4:33to matter a whole lot when we talk about interference later

4:35on in this skill.

4:36All right, so let's go and clear off our drawing here and talk

4:39about the concept of frequency.

4:40Frequency is a huge part of any Wi-Fi communications

4:44conversation.

4:45And you probably are familiar with this already, and just

4:47from the idea of a 2.4 gigahertz network versus a 5 gigahertz

4:51network.

4:52Anytime we're talking about the concept of Hertz, that's

4:54a frequency conversation.

4:56So what we have here when we're talking about frequency

4:59is frequency is really asking us to measure the number of cycles

5:03per second.

5:05And that's an interesting way of saying it

5:08because ultimately this concept of cycles

5:11doesn't have a unit of measurement.

5:12This isn't something like distance over time

5:15like meters per second would be.

5:17Instead, it's just something divided by seconds.

5:20And so really what we're talking about here

5:23is a one over second type of way of measuring this.

5:26And so this measurement, this unit of measurement,

5:28one over second, this is the concept of a Hertz.

5:32Now, Hertz is not a plural form of the word hurt, OK.

5:38This is named after a scientist named Heinrich Hertz,

5:43and so we're talking about a last name.

5:45And so this is why we always capitalize the H in Hertz.

5:48It's just like we typically like to do

5:49if we have a unit of measurement that's named after somebody.

5:53And so we're going to abbreviate this as capital

5:55H and then a lowercase z.

5:58And so what we're going to now look

6:00at here is, OK, well, what do different frequencies

6:02represent?

6:03So if I were to say that this entire wavelength occurs

6:07over one second, we can count how many cycles there were.

6:11So I see one cycle here, and then I see a second cycle here,

6:16and then I see most of a third cycle.

6:19So maybe we'd say, like, it's close to three.

6:22I'm just going to count that as being done.

6:24So let's say that this in one second we

6:26got three different cycles.

6:28So the frequency of this waveform

6:31is going to be 3 Hertz, because it's how

6:34many cycles per second.

6:36And so as we start to ramp up the frequency,

6:38we're going to see that we get a whole lot more cycles in there.

6:41For example, I could draw a waveform in here

6:43that is roughly twice as fast.

6:47And so if I were to squeeze in, for example--

6:49wait, let me just make sure I'm doing this right.

6:52Yeah.

6:52So now I've got two waveforms in here.

6:54I know the amplitude got a little funny there,

6:56let's do that again.

6:57There we go.

6:58So I got two waveforms in here, two waveforms and another two

7:02waveforms.

7:04I know it's not the prettiest.

7:05But ultimately what we're saying here is I've got,

7:081, 2, 3, 4, 5, 6 different waveforms,

7:12so now I'm at 6 Hertz.

7:14So I just doubled the number of cycles

7:16that are on this waveform within the exact same time period.

7:21And so I can get faster and faster and faster.

7:23And so I could get to the point where I have 1,000 cycles,

7:27and so that would be 1,000 Hertz.

7:28And we can abbreviate that.

7:31We can say that this is actually one kilohertz

7:34because the cake for kilo is representative of the fact

7:38that it's 1,000.

7:40And so if I have 2000, I would have two kilohertz,

7:42if I have 1,000 thousands, well now we're

7:44talking about a million, and that would be a megahertz.

7:49So one-- let's just try that out with six zeros,

7:52one million Hertz is going to be megahertz.

7:56And then same thing.

7:58We can do a billion and say now we've got one

8:01with nine zeros after it, that would be 1,000 millions,

8:06so that's a billion.

8:07And that would be one gigahertz.

8:10And so when we're talking about Wi-Fi

8:13occurring in the 2.4 gigahertz and 5 gigahertz space,

8:16this is what we're talking about.

8:17We're talking about how many cycles there are per second.

8:20And gigahertz is in the billions,

8:22if we can believe that.

8:24And truly billions of these waveforms happening

8:28or these cycles happening within a single second of time.

8:32And so this is what we're talking about when it

8:34comes to light and frequency.

8:36Now, just for the fun of it, I like

8:37to compare our Wi-Fi signals to visible light,

8:40because we're very familiar with visible light.

8:42And so we've got red and we've got--

8:45well, really, it's just the ROYGBV concept.

8:47Red, orange, yellow, green, blue and violet.

8:52And I believe we got rid of indigo at some point.

8:54When I was young there was an I in there

8:56but we'll just leave it as ROYGBV.

8:58All that to say when we're talking

9:00about the visible light spectrum, this

9:02ranges from, believe it or not, 400 terahertz

9:07on the red end, that's the low end.

9:09And we go up to 800 terahertz here

9:12on the high end where we have violet light.

9:14And so when we talk about a terahertz,

9:17well, a terahertz is just like in the world of computer data.

9:22A terabyte is 1,000 gigabytes, so a terahertz

9:26is 1,000 gigahertz.

9:28And so ultimately when we're comparing, for example,

9:305 gigahertz of Wi-Fi, which is on the higher

9:33end of our frequency spectrum, we

9:35can actually do have six gigahertz now,

9:36but we're comparing 5 gigahertz in Wi-Fi

9:39to truly 400,000 gigahertz as the low end

9:45of our visible light spectrum.

9:48And so this is shows the comparison

9:50of how much lower frequency our Wi-Fi

9:54is relative to the visible light spectrum.

9:56All right, let's wipe out the chalkboard and talk

9:58about one last concept which is important,

10:00which is the wavelength.

10:02The wavelength of a waveform is sort of like the period,

10:05in that I'm going to take any point on the waveforms,

10:07let's just say right here in the middle and close to origin.

10:10And we'll measure to that same spot at the end of the cycle.

10:13But rather than measuring the amount of time that it takes,

10:16we're going to measure the actual physical distance.

10:19And so typically when we're talking about wavelength,

10:21we're measuring this in terms of meters.

10:24Now, sometimes that's literal meters,

10:26sometimes it's larger than meters.

10:28We could be talking about kilometers.

10:29But a lot of times we're talking about something

10:31smaller, something more in the range

10:33of millimeters or micrometers, or even nanometers

10:36and picometers.

10:38And so just depends on how much frequency we have,

10:42because wavelength is actually going

10:44to be tied in parallel here a little bit

10:46to the concept of frequency.

10:49So what do we mean by comparing wavelength and frequency?

10:51Well, they're going to be inversely proportional

10:53to another.

10:54Because if we think about it, if I'm

10:55going to increase the frequency, then that

10:58means I'm going to take this waveform

11:00and I'm going to get two separate cycles

11:03within the same amount of time that

11:05would have taken for us to do one cycle.

11:07Well, if I'm measuring now from this part to this part,

11:10we'll, compare that line to this line down here.

11:13We just see that we shrunk that line roughly in half.

11:17Because we squeezed our waveforms together,

11:19so we could fit more in there, so now we've

11:21got two times the frequency.

11:23However, now our wavelength has actually trunk in half.

11:27And so that's why they're inversely

11:28proportional to another.

11:30Now the other thing to consider is the fact

11:31that since we're measuring physical distance here

11:34and we're talking about so many cycles per second,

11:38we've got a one over second here.

11:40But we can actually relate this back

11:42to the speed of the waveform, because speed

11:44is going to be some amount of distance

11:46divided by some amount of time.

11:48So if we have a frequency and we want to know the wavelength,

11:51we can do that so long as we understand what the speed is.

11:54Well, this is why it's important we have that conversation

11:56already.

11:56We know what the speed of this waveform is.

11:59The speed of this waveform is going

12:01to be the speed of light, that constant C

12:04that we talked about.

12:05So the equation to compare wavelength and frequency

12:08is simply that the speed of light

12:10is equal to the wavelength, which we represent

12:12with the Greek letter Lambda, times the frequency, which

12:15we usually use a cursive f for.

12:18And so it just sort of a curvy f I suppose,

12:20if you want to call it that.

12:21But ultimately, if I've got the frequency of something--

12:24so remember what we said about it being 3 Hertz earlier.

12:28But I've got 3 Hertz for the frequency,

12:30and I know what the speed of light is, it's that 2.99 times

12:3310 to the eighth meters per second.

12:35Well, now I can calculate out the wavelength.

12:38I can do my quick algebra here and say

12:40wavelength is equal to the speed of light

12:43divided by the frequency.

12:44And what's interesting here is that we can basically

12:46round this to three, and that's because that's exactly what we

12:49have here, is three Hertz.

12:50So we'd say that this is equal to--

12:52just, again, we're estimating, 3 times 10 to the eighth,

12:55divided by 3.

12:56So the 3's are going to cancel out.

12:58And so we're left with 10 to the eighth meters.

13:01Now 10 to the eighth just means that we have 10 zeros,

13:03so we're talking about hundred and then three zeros here and 3

13:07zeros here.

13:08So that would be 1,000, million, 100 million meters.

13:12And so that's a very, very long wavelength.

13:16I mean, I don't think that we can really understand just how

13:19big of a wavelength that is.

13:21And so if truly we set an RF wave to behave,

13:25to operate at 3 Hertz, the size of our wavelength

13:29is going to be enormous.

13:31But as you can imagine, as we start

13:32to increase the frequency of that light wave,

13:35well, then this wavelength is going

13:36to start to drastically shrink.

13:38Now, just like before, I like to compare this

13:40to the visible light spectrum to get an idea of what

13:43we're talking about here.

13:44Because on the Wi-Fi side of things,

13:46we've got a wavelength of about six centimeters,

13:49this would be four 5 gigahertz Wi-Fi.

13:52If I take this equation and I replace

13:55my 3 Hertz with 5 gigahertz, which, again,

13:57is 5 billion Hertz, well, now that wavelength

14:01is going to get a whole lot smaller,

14:02and it's all the way down to six centimeters.

14:04Which is still something that I can see.

14:06I mean, I can look at my hand and estimate

14:08what six centimeters might be.

14:10And so this here is Wi-Fi.

14:12However, when I think about visible,

14:14light visible light is operating much higher frequencies.

14:18Remember we talked about 400 terahertz and 800 terahertz.

14:21And so visible light is actually going

14:23to range between 400 and 700 nanometers.

14:27Nanometers is one billionth of a meter.

14:30And so these are teeny, teeny, tiny,

14:32far smaller than the naked eye could ever perceive.

14:35And so we're talking about six centimeters

14:37all the way down to the nanometer scale,

14:40that is much, much smaller.

14:42And so sometimes it's telling to see just what we're

14:44talking about when it comes to the reds and blues that we can

14:47see, versus what exactly these access

14:50points and these wireless devices

14:51are using to communicate with one another.

14:53So when we think about the anatomy of waveforms,

14:55we do need to understand concepts

14:57such as the crests and the troughs

14:58and where the origin is and the amplitude.

15:00Amplitudes is going to be a big one, as well as phase.

15:03But then we also need to think about frequency and wavelength.

15:06So we'll start with frequency here.

15:07It's the measurement of the amount of cycles over time,

15:11and we use the unit of measurement

15:13called the Hertz in order to measure that.

15:15So if I can count three seconds or three cycles

15:18within a second, that tells me that I'm operating at 3 Hertz.

15:21And so when we look at something like Wi-Fi operating

15:24in the billions of Hertz, that tells us

15:26how many cycles are happening within just a single second.

15:30Now, likewise we need to consider wavelength.

15:32And wavelength is inversely proportional to frequency,

15:35meaning a frequency increases, wavelength

15:37will always decrease.

15:38And at the same value, relative value.

15:41So frequency doubles, wavelength halves.

15:43If frequency triples, then wavelength is divided by three.

15:47And we see why we've got this relative to the speed of light.

15:50It's just like basically how we do math

15:53when it comes to these sinusoidal waveforms.

15:55Now, wavelength is the length of a cycle

15:58in actual physical distance.

16:01And so even though we can't see light waves

16:03and we can't necessarily measure them with a measuring stick,

16:07we can run the calculations, like we talked about,

16:09to figure out how exactly long those wavelengths are.

16:12I hope this has been informative for you,

16:14and I'd like to thank you for viewing.

0:05Well, as it turns out, our light waves

0:07can behave at pretty much any frequency.

0:09We're talking about really, really low frequencies

0:11like my 3 hertz example to really, really

0:13high frequencies.

0:14But we're not just talking about gigahertz and terahertz.

0:17We're talking about much, much greater frequencies.

0:20So when look at small frequencies

0:22to very large frequencies, this forms

0:23what we call the electromagnetic spectrum.

0:26In this video, we want to take a look

0:27and see what exactly the spectrum is, where

0:29on the spectrum our Wi-Fi falls, and then start to understand

0:32how it all ties together.

0:34Let's take a look.

0:35As humans, we are actually able to tell what frequency light is

0:38behaving at because different frequencies of light turn

0:41into different colors for us, and so even the yellow

0:44of my pen that I'm using right now is a different frequency

0:47than, let's say, the blue of this text up here,

0:49and our eyes are able to distinguish that

0:51so long as our eyes are working like they're supposed to.

0:54And so oftentimes what we can compare this to

0:56specifically is the rainbow, and I already

0:59mentioned the colors of the rainbow before.

1:01We had red, orange, yellow, green, blue--

1:04sometimes we throw indigo in there-- and then violet.

1:07And we see this specific range of colors, especially when we

1:12look at, for example, a rainbow in the sky

1:14and we see all of these different colors lined up

1:16with one another.

1:17Well, that's because of the frequency of light.

1:21And so what we're really saying is

1:23that red is the lowest frequency of light and violet

1:26is the highest frequency of light, where orange

1:29lies somewhere in the middle.

1:30But orange is less than yellow, and yellow is less than green

1:33and so on and so forth.

1:35And so it's pretty fascinating how

1:37we can interpret different frequencies

1:39as different colors.

1:40But even more fascinating is the fact that there are just a ton

1:44of frequencies that we cannot see,

1:46and those would be frequencies that are lower than red

1:49and frequencies that are higher than red.

1:52And so we have to be really cognizant,

1:54I suppose, of the fact that the electromagnetic spectrum

1:58is so much bigger than we can perceive with our human eye.

2:02And so it's lovely to look up into the sky

2:04and see these beautiful rainbows,

2:05but there's a whole lot of other colors that we just can't see.

2:09And so when we talk about these colors--

2:11or maybe I should call them frequencies--

2:14what we find is that we can go as very,

2:16very low as we want down to, again, a single hertz, 1

2:20hertz, 2 hertz, 3 hertz.

2:21And then we can go higher than what

2:23we can see, so even starting with terahertz

2:26and going to petahertz, for example, and exahertz.

2:28And we can go all the way up to, let's say, something times

2:3210 to the 18th or times 10 to the 20th hertz,

2:35and we're talking about an enormous number

2:37of cycles per second.

2:39And because this is a spectrum, we

2:40tend to break this down into what we call regions,

2:44and so I'm just going to throw some barriers up

2:46here and understand that when we're

2:47talking about a particular region

2:49we're talking about a range of frequencies

2:52that our signals would be classified as.

2:55And so we can start right away by talking

2:57about the regions directly outside of red and violet.

3:01And we have special names for those,

3:03and you've probably heard of them.

3:04We have the infrared region, and we have the ultraviolet region.

3:09Now, infra, if we look at the English word there,

3:11what exactly is that saying?

3:12Infra means below, and so infrared has always

3:16been talking about the fact that it is the frequency

3:19region below red light.

3:21Likewise, ultra-- we talk about ultra.

3:24Some superheroes seem like they have ultra in their name.

3:26It means above.

3:28It means high.

3:29It means-- maybe we like to think of it as powerful,

3:31but ultimately it's the opposite of infra.

3:34Infra means below.

3:36Ultra means above.

3:37And so we're talking about ultraviolet.

3:40This ultraviolet region means that it has

3:42a higher frequency than violet.

3:45And so these are the first two regions

3:47that we tend to talk about a little bit

3:49because we're concerned about UV rays.

3:51We need to be careful with that because they can give us

3:54sunburn and some even worse health

3:57effects as a result of being exposed

4:00to high levels of frequency, these radiation types.

4:04And so as we look higher than ultraviolet,

4:07we get into the X-ray domain, and X-rays--

4:11a lot of us are probably familiar with those just

4:13from the medical world perspective.

4:15I know I can go into the hospital.

4:16I can get an X-ray of my broken hand.

4:18It'll show me all of my bones.

4:20But really what they're doing is they're shining X-rays

4:23through my hand against a photoelectric plate that's

4:26essentially going to capture an image of what's

4:29happening inside of my hand.

4:32And so that's why we have to use X-rays for that.

4:35But again, this is like UV.

4:37It's very, very high frequency, and so we've

4:39got to be careful with this.

4:40It has very negative health effects,

4:42which is why hospitals are tracking

4:44how many X-rays we have.

4:45And the attendant who manages the X-ray-- they

4:49have to run behind a shield because if they're

4:51exposed to X-rays constantly that would be very dangerous.

4:54And then we have gamma rays up here.

4:57Yes, if you follow comic books you probably

4:59have heard of gamma rays, but that's

5:01the comic book version of it.

5:02There are real-life gamma rays.

5:05We don't have any practical uses for it that I'm aware of.

5:07I'm sure there's something out there for these,

5:09but ultimately, gamma rays are just anything above X-rays.

5:13So it just kind of keeps going and going.

5:15And so now we look at something--

5:17at the frequencies lower than infrared,

5:20and the biggest one is right-- whoops,

5:23I started spelling the wrong one.

5:24The biggest one is the microwave region,

5:27and so, yes, this is where our microwaves that we

5:30use in our kitchens operate.

5:32And that's one good.

5:33Other than-- we can possibly think

5:34of something more applicable to the course, which is Wi-Fi.

5:37This is where we fly lives.

5:40It lives at a much lower frequency even than infrared,

5:43let alone visible light.

5:44And so when we talk about the health implications of Wi-Fi,

5:48the reason why science says that Wi-Fi radiation is safe

5:52is because not only is it below the frequency of some

5:56of these dangerous rays like ultraviolet and X-rays,

5:59it's actually lower than the frequencies of visible light.

6:02And so we're not just talking light from the sun

6:05because that has ultraviolet light in it,

6:07but we're talking about just the colors that are reflecting off

6:10of my walls having much, much higher frequency, we just said,

6:15400,000 hertz or 400,000 gigahertz, rather, versus the 5

6:22gigahertz that my Wi-Fi is operating at.

6:24And so when we talk about the wavelengths--

6:28the wavelength is like 6 centimeters.

6:30That's a pretty large wavelength.

6:32And so we're not as concerned about Wi-Fi signal causing

6:35damage in the same way that UV and X-rays--

6:38they can actually jump into our cells

6:41and destroy parts of our cells.

6:43So from a health perspective, that's why we say it's safe.

6:46It's the same reason why we say using microwaves

6:49in our kitchen-- that it's safe for using

6:51on food because all it's doing is heating up the water.

6:54It's not actually injecting radiation into our food.

6:57It's in the same way that shining a flashlight

7:00on our food wouldn't actually cause our food

7:03to have problems.

7:05And so the last region down here-- this

7:07is what we call radio waves.

7:08The reason why it's called radio waves

7:10is because we use these for broadcasting radio and TV.

7:16And so especially back before streaming services

7:20and when we have an antenna outside of our house

7:23and we're receiving signals for our radio--

7:26in fact, we still use this in our cars

7:28extensively when we're tuning into the radio, et cetera.

7:31That's where we're getting our signals from.

7:34And so they operate in the radio space.

7:37But again, as I mentioned earlier,

7:39I think some people hear radio waves

7:41and assume this has to do with audio.

7:43It has nothing to do with audio.

7:44It can convert into a data, and so that data

7:47can be a picture like on our TV.

7:49It can be audio like the TV audio.

7:51It can be audio like our radios.

7:53But ultimately, it's doing exactly what

7:55Wi-Fi does, which is encoding information

7:58into these different waveforms.

8:01And it's operating at such a low frequency

8:03that, number one, it's very, very safe,

8:05but also, number two, it can go really, really far much, much

8:09further than any of the waveforms that are in a higher

8:13part of the spectrum.

8:14And so that's the other part we want

8:16to talk about here is how frequency relates

8:19to our distance because as we might imagine,

8:23it doesn't do me much good if my house where I've got my TV

8:28antenna up here, let's say--

8:30so I'm not sure how to draw this TV antenna.

8:32There we go, some kind of Yagi antenna.

8:34And I need to be as close to the TV station with a big antenna

8:39on it or what have you.

8:40I need to be this close to the TV station

8:42just to get that signal in the same way that

8:45need to be right next to an access point

8:47to get Wi-Fi signal.

8:48Now, instead, we want this to be miles or many, many kilometers

8:52away.

8:53In fact, we need this to be sometimes in adjacent cities,

8:57and so this is why the lower frequency

8:59is used, because the lower the frequency,

9:02the greater the distance that signal can propagate

9:05using the same energy levels.

9:07And so this is why, if I step out of my house

9:09and I just take a few steps away sometimes,

9:12my Wi-Fi doesn't quite make it out

9:14of my house to my outdoor area.

9:16Now, I might see my neighbors' Wi-Fi or something

9:18along those lines, but oftentimes the quality

9:20is very, very low.

9:22And certainly I'm not going to be

9:24able to get it miles away from my house,

9:26and so that's because we're using a much higher frequency.

9:30We're using that 2.4-gigahertz frequency or the 5 gigahertz

9:34or now the 6-gigahertz spectrum, and so these are much higher

9:37frequencies than my radio and TV waves are using.

9:41Now, this doesn't just affect our distance.

9:43It's also going to affect our propagation.

9:46When I say propagation, really I'm

9:47talking about through things.

9:48So we're talking about walls.

9:50We're talking about buildings, whatever

9:53it is that's impeding our path.

9:55And so once again, I might have a bunch of houses,

9:58or I might have a building here between the TV

10:01station and my house, and this signal

10:02is going to pass through just fine because of the lower

10:05frequency.

10:06And the same way that my Wi-Fi--

10:08I might have my floor plan look something

10:10like this, where I've got a hallway here.

10:14And I've got the access point in the hallway,

10:16and I've got two rooms right next to this access point.

10:19Well, I'd expect that the access point

10:21is going to be able to communicate into these rooms.

10:24It can communicate through walls because it's

10:26a much lower frequency than all of these frequencies

10:30up here, even visible light.

10:31So this is one reason why visible light

10:33can't go through walls.

10:34However, visible light, we understand,

10:36can go through things that we might call translucent.

10:39Translucent means that I can get partial amounts of light

10:42through something.

10:43So maybe I think about a candle.

10:46If I shine a flashlight against a candle,

10:48I can see that light go through the candle.

10:50I can even see the flashlight go through my hand to some extent.

10:53Visible light is able to go through some materials.

10:55But certainly, as we get into UV and especially X-rays and gamma

10:59rays, it's much harder for those types of radiations

11:03to penetrate things.

11:04That's why we use lead vests when

11:06we're taking X-rays because it blocks those X-rays solid.

11:10It makes it so that they can't get through,

11:11whereas certainly a radio wave is

11:13going to be able to go through that same type of shield.

11:16So understanding that the higher the frequency

11:18we get the lower the distance that our propagation is going

11:21to go and the more that walls, and buildings,

11:24and obstacles are going to impede our communications.

11:28So when it comes to our key takeaways, one of them

11:30is simply going to be that it's really cool how our eyes can

11:33detect different frequencies of light

11:35by representing them to us as different colors.

11:38So when we're seeing blue versus red,

11:40we're truly seeing completely different frequencies.

11:43Red is as low of a frequency as we can see,

11:45and blue, especially violet, is as high of a frequency

11:48as we can see.

11:50So next, the electromagnetic spectrum we see is--

11:53yeah, it's got the visible light right there in the middle,

11:55but it really goes very, very far, way higher and way lower

11:59on the spectrum.

12:00And so it's important that we can

12:02identify the different regions and especially

12:03understand that Wi-Fi communications,

12:06and cellular, mobile data, those kinds of things--

12:09they all operate within the microwave

12:11part of that spectrum.

12:13Now, lastly, as we talked about, the higher the frequency

12:16goes, the less far that those waveforms are

12:21going to be able to propagate.

12:22So it's going to have more problems with obstacles.

12:25It's going to have problems even just in free space,

12:27just trying to get across things.

12:29But ultimately, this is why we use the lower frequencies

12:32for our communications, because we

12:34want our communications to be able to go certain distances.

12:37And so when we look at the applications, sure,

12:39TV and radio--

12:40that might be coming from the next city over.

12:42It needs to be a very low frequency

12:44so that those waveforms-- remember

12:46how long those waveforms can get at the lower frequencies.

12:49They are going to have an easier time passing through obstacles,

12:52whereas then as we get into higher levels of radiation

12:55or higher levels of frequency, that's going

12:57to be harder and harder to do.

12:58I hope this has been informative for you,

13:00and I'd like to thank you for viewing.

0:05Well, we have reached the end of a skill.

0:07So let's take a moment to review what we've learned with a quiz.

0:09First up out of three questions, what letter

0:11is used to represent the speed of light in physics equations?

0:14And by the way, please hit the pause button

0:16and make sure that you have given yourself enough time

0:18to answer each one of these questions as we

0:20go through them.

0:26So the answer here is C. Remember that famous equation,

0:30E equals mc squared, where that C is representative

0:33of the speed of light.

0:34And the speed of light is a constant

0:36that we measure out to be roughly 2.99 times 10

0:40to the eighth meters per second.

0:42Now, a lot of this specific knowledge

0:44isn't really required for being a wireless engineer.

0:46However, if we don't understand these basic physics concepts,

0:49it is going to impede our understanding of what's

0:51really happening when we talk about wireless communications.

0:54Next question, a wireless waveform

0:56has a frequency of 3 gigahertz.

0:58What is the wavelength?

1:04So remember our equation, the speed of light

1:06is equal to our wavelength, which

1:08is represented by that Greek letter

1:10Lambda, times the frequency.

1:12And so we know what the speed of light is.

1:14We understand that it's, in this case

1:16we'll call it, roughly 3 times 10 to the eighth.

1:18That'll make our math a little easier.

1:20And then we say equal to the wavelength

1:22times the frequency in this case, which

1:24would be 3 gigahertz.

1:26Now, 3 should be multiplied by 10 to some kind of power here.

1:30So what are we talking about?

1:31Well, kilohertz is equal to 10 to the third power.

1:36That would be 1,000.

1:37Megahertz would be a million, that's 6.

1:39Gigahertz is a billion, which is 9.

1:41Those would be 3 times 10 to the ninth.

1:44And so, at this point, it's just algebra.

1:46So we can say that wavelength is equal to the value of C,

1:50here, 3 times 10 to the eighth, divided by 3 times 10

1:54to the ninth.

1:55And so this is going to make for some pretty easy math here.

1:57We cancel out the 3's.

1:59And 10 to the eighth divided by 10 to the ninth,

2:01this is going to result in 1 over 10.

2:04And so it's a tenth of a meter.

2:06Always remember that it's measured in meters.

2:08So this is 0.1 meters which we could

2:10call 10 centimeters if that's how we want to write it out.

2:14But ultimately, this is going to be our answer.

2:16So at this point, it's more about just

2:19understanding how we go about calculating it.

2:21We need to remember this equation right here

2:22and be able to do the math when we're asked to do so.

2:25OK.

2:26Last question, which type of electromagnetic radiation

2:28will have the shortest free space propagation?

2:36Let's remember the relationship that we defined here.

2:38If we increase the frequency of our light waves

2:41then we are going to find that we can't quite go as far,

2:44our distance is going to overall decrease,

2:46not just in free space, by the way,

2:48but also through objects in most cases.

2:50And so at this point, what we need to understand

2:52is how is the electromagnetic spectrum laid out.

2:55And so we've got the visible light right here in the middle.

2:58And from here, we recall, we've got infrared and ultraviolet.

3:02And so we can put those there.

3:03And then we've got x-rays and gamma rays.

3:05And then we have the microwaves and the radio waves.

3:08And so as we look at these various options,

3:10we see x-rays all the way over here.

3:12We see visible light is lower than the x-rays.

3:16And so that's not going to be an answer.

3:17Radio waves are all the way at the bottom,

3:19and microwaves are just right above it, which by the way,

3:22remember, this is where Wi-Fi exists, is inside

3:25of the microwave region.

3:26So when we compare all of these answers,

3:28x-rays would be the highest frequency

3:30on the electromagnetic spectrum.

3:32And so that is going to be our answer.

3:34So that wraps up our quiz.

3:35If you found that some of this information

3:37didn't quite propagate properly then be sure to go back

3:40and review the information that we discussed in order

3:42to get it all down.

3:43Otherwise, congratulations on completing

3:45Define the Characteristics of Radio Frequency.

3:47I hope this has been informative for you.

3:49And I'd like to thank you for viewing.