Fundamentals of RF

6. Wavelength Part1

I should also say you don't have to be an amathematician to understand this, but in a sine wave, you know, we used to have what this mathematical film used to have. I guess we still do, called trigonometry. I kind of liked trigonometry, at least from what I remember. And I remember we were always looking at things that were like a triangle and trying to figure out what these angles were. And we'd use things like sine, cosine, and tangent to do all that. I'm sure all of you just love talking about this math again, so I just took you back to junior high. Anyway, when we think about that, I'm bringing this up to just kind of get an idea of why we had these measurements in between called 360 degrees on a sine wave. So basically, when we see the peak, the positive, and the next peak, the next positive signal, the distance in between that we are going to say is 360 degrees. Now, that, by the way, does not tell us what the well, it begins to help us understand the wavelength,because the amount of time it takes to get from one peak to the next peak, I should say, the number of times you do that over a second tells us what that wavelength is going to be. But technically, we call that frequency a wavelength, which really is just the distance between two successive crests of that signal. How many times that happens is where we come up with the word frequency. Now, remember, because of AC, alternating current,that we can have this continual change between a positive and a negative. And if the power source were to change that current, it could make the wavelength longer or shorter. That's the other reason why we like using AC.

7. Wavelength Part2

All right. So when we look at wavelength, there are three main components that we talk about: frequency, which is how often we see those peaks over a certain amount of time, and then the distance between those peaks, which is the wavelength. So are frequency and wavelength length, which means that they have some relationship to each other. Remember the wavelength, the distance between the peaks, and how often that occurs over time. That's the frequency. And for some other reason, I guess, we have to talk about the speed of light, because these radio frequencies are wavelengths and they do travel at the speed of light, which in this case,they're going to use a constant of 300 million. It does seem a little bit fast. All right, then we have different characters, right? F for frequency, C for the speed of light. And then I think that's lambda, the measure in meters. And so what we look at is if I want to be able to see, and this is what they mean by inverse understanding some of the different formulas. When we want to calculate the wavelength,I'll put the W over here. Then we're going to divide the speed of light by the frequency, meaning how often the peaks occur over a certain amount of time,or if I wanted to find the frequency. Now, by the way, this is just simple algebra, right? It's the same three components. We're just looking at the different variables. So the frequency then is going to be the speed of light divided by the wavelength. A better way of thinking about this without actually putting big numbers in there, and for me to try to start actuallydoing math with 300 million in front of you, is that we could say that the higher the frequency of a signal, the smaller the wavelength of that signal. So think about it. We're taking all right. I just promise not to do this math, but I'm going to have to just to help make sense of this. So if the first formula for wavelength is right, it says the higher the frequency, the smaller the wavelength. So if I have this speed of light, and F gets bigger, I mean, think about it. I'm just picking numbers that we wouldn't use, which would be much larger numbers. But you can see that the higher this gets, the wavelength is a smaller number, right? That's basically showing you that I have more frequency. Now, if I were to do that division here,I'd be taking off a bunch of these zeros,and so the wavelength is going to be smaller. Now, on the other hand, when I'm looking at the frequency, and I take, let's say, 300 million, put my commas in there, we're going to say the same thing is that the larger the wavelength, meaning, again, if I just use the number ten as an example, The larger the wavelength of that signal, the lower the frequency of that signal is going to be. And that makes sense to me because we said that frequency is how often the peaks occur. So if I have a large wavelength, that means there's a larger distance between the peaks. And so my frequency, because it's not going to occur as many times in 1 second, then my frequency is going to get lower and vice versa. I'll make another little chart. If my frequency is very high, then the distance between the peaks, the wavelengthis also going to get smaller. Mahler

8. Wavelength Part3

When we talk about wavelength, you might have heard that at least the appearance that a lower-frequency signal is going to travel farther than a higher-frequency type of signal. Now, in reality, if we were out in outer space,each signal would travel the same amount of distance. It just depends on things like atmospheric qualities, rain,fog, maybe inside the office, going through walls. Yes, we can see that lower frequency signals will go further than those that are of higher frequency. But what I'm trying to say is that when we really think about the energy of these signals, that it's kind of like throwing a pebble into a clear lake where it's calm on the surface, I might say, okay, here's my lake. You know, maybe I've got my boat out there. No, I can't have my boat out there because it's got to be calm. And if I throw a rock or a pebble into the middle of that lake, you're going to start seeing the little ripples. And those ripples are going to be pretty big at first because they don't have to cover as much of an area. And as it radiates away from that, you can see those ripples slowly getting smaller and smaller until it gets to a point where you don't see them anymore. Now, that doesn't mean the energy, the original energy that I used or created when that rock went into the water. But if you notice, as I'm making these rings,that amount of energy at first was over a small area, but as it radiates out, that same energy has to cover more distance. And so that's why the ripples appear to get lower and smaller and smaller until at some point we don't see them anymore. And that doesn't mean that energy is still not there. It's just no longer perceptible. And we have that same issue when we talk about things like wireless communications with an access point. If we assume that it's sending a signal, omnidirectional at first or when I'm closest to the access point, it's a very strong signal and I get good reception and everything is great. And as I move farther from that access point, that energy,as I said, again, has to go farther, right? The circumference of this circle that I'm drawing gets bigger and bigger. And so at some point, I just probably wouldn't even be able to see the signal because it's travelled too far and it's become, well, we think of it as being weaker, but it's just not as measurable or perceptible, which is how these wireless communications work. And then when we add things like walls and everything else, that's where we might see that idea that a lower frequency travels than a higher frequency. And we're going to talk about some of the problems that we have when we start seeing these different obstructions to our signals. And some of the effects that it could have.

9. Wavelength Part4

So if you think about the different wavelengths that we're going to use, the 2.4 GHz or the 5 GHz for our WiFi connectivity,they are going to have different wavelengths. One's going to be lower at 2.4 versus 5.0, which is obviously higher. And we can actually measure the distance when we look at the peaks of each of these signals. We can measure the distance to know how far apart each of these peaks are. As an example, at two four peaks, which we didn't see the rest of, the distance there is about, well, hopefully exactly 482 inches. And I know that sounds kind of weird when you think about radio frequency, about the peak. The positive part of that signal actuallyhas a measurable distance as it's travelling through air that we can recognize. And we get to a higher frequency with a 5 distance between those two peaks because it is a higher frequency of the wavelength. Then remember what we said; the higher the frequency, the smaller the distance between the wavelengths. In this case, it is 2.04 inches. And that will continue. You'll continue to see those with almost any frequency. You could probably look it up or do the mathematical equation you saw a little bit ago with the lambda and the F and the speed of light to be able to come up with an idea about what this wavelength looks like.

10. Frequency Part1

Now, as we have said, frequency is the number of times a specified eventoccurs within a specified time interval. Now, what we've been talking about, where the peaks of that signal and how frequently we see those peaks over the time interval, usually measured in seconds, But technically, the definition of frequency, like I said,is how many times something happens over time. We measure frequency in a term that we call hertz, named after the person who really came up with this idea. And when we think about 1 Hz, then what we're saying is that we would see one cycle per second. When we get into higher frequencies, like a kilohertz,then using the metric idea here, a kilo means a thousand times, or a thousand cycles per second. A megahertz would be a million cycles per second. A gigahertz would be 1 billion cycles per second.

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