CWNP CWNA – Components and Measurements of RF

1. Components and Measurements of RF

In this module, we’re going to make you mathematicians, whereas in other parts of the course, we’ll make you physicists. So I hope that you have your mathematics hat on, and we’re going to talk about the components of RF communications, and we’re also going to look at things like not only the components but how they work together to help us get a certain type of strength of signal. And we’ll look at those power units and compare them. Then we’re going to get into RF mathematics, and instead of making you have to do really high-end math and utilise different types of strange division types of numbers, we’re going to make it easy for you. But first, we’re going to show you the hard way, and then I’ll show you the easy way with the rules of tens and threes.

2. Components of RF Communications

Now there are many components that contribute to the success of the transmission and the reception of a radio frequency signal. So if you think about it, there is some device, a laptop computer, or something else that is sending data into what we would call the transmitter. The transmitter here is the thing that’s going to have that AC power and is going to be responsible for how it basically sends out the signal so that it can be interpreted as ones and zeros, which we call the modulation.

But from that transmitter, we have this copper cable. We call it the antenna cable that the power has to go through. Now, if you think about it, anytime we start sending current over a cable, there’s going to be a little bit of a loss of power. It’s the physics; it’s the travelling distance. That electrical signal is going to get a little bit weaker, and we’re going to talk about that and why that’s important to us as we move into the math. And then we have this thing called the intentional radiator.

And what that will do is basically direct that power to the antenna. And depending on the design of the antenna and the type of power that’s being sent, we’re going to come up with what we call the EIRP, or the actual strength of the radio waves. And that antenna is then going to either omnidirectional or more focused, depending on the type of antenna, send that signal across the air, hoping that the receiver over here gets it.

Now, what are they going to basically do? That receiver is going to be able to translate that message as a bunch of ones or zeros and basically send it back to the sender. I should say the antenna. And then from there, it’s going to go back to the receiving device that wants to see that data. Now, as we look at this picture, and you’ll see it a couple other times, we’re going to start talking about how the different components can affect the overall power and quality of the signal that we’re going to send.

3. Transmitter

The transmitter is considered the initial component in the creation of a wireless medium. Now, really, to me, the initial part of it was that computer, or endpoint, that was sending data to be transmitted. But when it gets into the world of wireless, the transmitter is where it starts. So the computer is going to hand off that data, and the transmitter’s job is then to begin the RF communication. Remember, its job is to be able to create the radio frequency by the way in which it uses the alternating current, or AC. And that is very important to us for not only the frequency, the amplitude, and all the rest of the things we’ve talked about, but also the way in which it can modulate that signal to represent the ones and zeros. And so the transmitter is then going to be responsible for determining the power to be used. In fact, it’s going to be responsible for all parts of communicating the ones and zeros. Because when the antenna receives the power, it’s just going to create that radio frequency based on what the transmitter sent. So you could almost say that the transmitter is the brain of how we communicate.

4. Antenna Part1

Now, the antenna again provides two functions in the communication system. And I know some of you might say, “Hey, well, the spelling of antenna looks wrong.” We’re used to seeing an E. That’s just the plural form of the word antenna. Antennae have more than one anyway, so it’s an antenna. Anyway, we’re going to talk about just one or two functions that it has. One is that it’s going to be connected to the transmitter. So it’s collecting that AC signal that the transmitter is getting, and then it receives that power. And then it has to direct or radiate the radio frequency waves away from the antenna in a pattern specific to the type of antenna.

Often, we call it the isotropic radiator, or IR. Now, when I talk about the pattern, you have to remember that not all antennas send everything out in a kind of orb-shaped sphere. We’re going to get into those types of frequencies as well. But you might have some antennas, like a flashlight, that can direct or focus the light in a certain direction. Antennas can do that as well. Now, when connected to the receiver, this is another antenna on the receiver. The antenna is going to take that RF that it receives and the stuff coming from the transmitter and direct that into an AC signal into the receiver, where the receiver can then figure out what the ones and zeros are. So that’s where the receiver will then convert the AC signal to bits and bytes for the data to be sent to whatever end host wants to have it.

5. Antenna Part2

Now, there are two ways that you can increase the power output from an antenna. One is to generate more power from the transmitter, as I mentioned before, to direct or focus that signal that is radiating from the antenna. So, again, I would talk about my flashlight. Or for those of you in other countries, you’d call it a torch. The idea is that you’re right. We’re focusing that light. If it were just a standard, lone bulb, it would certainly not be as bright as when we focus it.

6. Receiver

So to kind of put some of this information together before we talk about the receiver, right, the AC power is coming from the transmitter. And like I said, we could go higher or lower with that power to get more, basically, out of that signal. When that power current strikes the IR, the intentional radiator, that is what the antenna will convert into radio waves. Now, as I said before, we could focus that energy another way to get more power, or we could just let it go out from a typical type of omnidirectional antenna, just let it continue to go out.

In either case, as long as there is enough RF signal for the receiver to hear, the receiver will take that signal from the antenna and correctly translate it. It receives the signal. It’s going to turn that into AC current to get to the receiver. And the receiver will be able to deduce the ones and zeros that it will send from the incoming AC current. So I put one over zero. That’s not a math term. I know it’s a bad division. That just means ones and zeros. But anyway, it’s going to turn that into data and send it to whatever device wants it. It contains the information.

7. Intentional Radiator (IR)

Now, the FCC for the United States does have definitions of what the IR, the intentional radiator, can do when it comes to the type of power used in the radio frequency. By the way, part of the definition of an IR is that the whole purpose of the device is to generate radio frequency instead of it being a byproduct of its main function. A byproduct might be that when you run a vacuum cleaner, the motor will cause some interference. It will send out some signals that could cause interference. But that was not the purpose of the vacuum cleaner. So it was just a byproduct of its function. On the IRS, the FCC is going to regulate the power levels that we can use. And when we get into the math, we’ll talk about why we measure things in milliwatts, but we also use the term “decibels,” which is a way of showing the relationship between the power and the milliwatts that we have.

And so we get in, like I said, when you get into that math, and you’re going to understand, I hope, the difference between decibels and this measurement in milliwatts, or the comparison. So we typically use one milliwatt as our starting point for what we’ll measure in decibels, and the decibels will help us see a relationship between one milliwatt, ten milliwatts, and 100 milliwatts. And I want to tell you so much right now, but it’s a little difficult because we first have to get through understanding all of these different measurements and then put them together in a big picture for you.

8. Equivalent Isotropically Radiated Power (EIRP)

One of the things we have to look at when we are designing our network is what the maximum signal strength of the radio frequency can be. and that is regulated by the FCC in the United States and, of course, similar agencies in other countries. But, as I previously stated, it is referred to as EIRP, or equivalent isotropically radiated power. And now, as I’ve just said, there are several ways that we can increase the strength of the radio frequency. One method is to use a higher electrical current or an alternating current, or to focus that beam.

However, whatever combination you use, you must ensure that you do not exceed the maximum required. And most of the vendors, by the way, make sure that their transmitter, in combination with whatever antenna you buy, will not be able to go over that maximum value. So unless you home-build your own transmitter and antenna, you won’t have to worry about going over that maximum EIRP. You just have to realise there are different ways in which you can increase that, as I said, from the actual electrical power, the AC current, or from the actual antenna.

So again, think of the flashlight idea. Perhaps you’ve seen this, or if you’ve ever used a nozzle on the end of a water hose, you’ve seen how you can focus that energy into a very tight stream, or you can start turning that nozzle and it gets into a wider beam, if you will, of less intense water. All of those together, plus, of course, how much water you’re pumping through the hose, would be the equivalent idea of what we can create with the combination of the transmitter and the antenna that we have to make sure that we don’t go over that certain amount of value.

9. Units of Power and Comparison

We’re going to be moving into some of the mathematics to understand some of the components that we need to use to get the coverage and performance we want. and a lot of that is going to be about the RF power. Now, as we’re measuring this, you may have already remembered that I talked earlier about the use of the term “milliwatt” to understand the amount of power. However, we then discussed decibels, which are a type of comparison unit.

And so for us to understand RF power, we’re going to be using mathematics and what we call a comparison to be helpful in understanding what that total power output is based on—even the distance you are from the antenna. Now, if I were to sit there and say, “Here’s this person,” and again, using stick figures as best I could, I could confidently say that this person is around six feet tall. And then we could talk about another person. And this person, we might say, is five eighths as tall as person A. I’ll put an A on their head. So one is an absolute measurement—exactly, they’re six feet tall. The other is a relative type of measurement, where we’re saying that in relation to person A, the other person is five eighths of that height. And we’re going to see that that’s where these ideas of decibels come in because we’re going to be doing some comparisons based on some of the actual numbers, such as milliwatts, versus then comparing what the strength of a signal is from a certain distance. So we’re going to do it a bit like Isa said, the hard way first, so you understand the exact types of formulas that are used. And then we’re going to get into some of these things we call the rules of threes and tens.

10. Units of Power

So when I talked about units of power, the absolutes are those things that we can measure, which is the term for a watt. We’ll define that here in just a little bit and then look at one thousandth of a watt, which is what we call a milliwatt. And remember, the milliwatts here are what we’re going to be using to measure the amount of power that we’re sending. Again, they’re absolute values that we know. Now, we are going to talk about decibels, which is a kind of relative term, but we do have a starting point of decibels that is going to be relative to one milliwatt. And when we get to the math, you’ll see what the actual relationship is going to be.

Now from there, the units of comparison The idea of a decibel is to really avoid the complexity of the mathematics that it would take to start working with numbers like one, one thousandth of a second, distance, and some other things. As a result, it’s only a relative way of describing. Well, in the world of music, you might have heard about how many decibels you can produce as far as sound, and I’m not going to get into the quality and all that sort of stuff, but really, a decibel is just a comparison of two or more sounds, or in this case, a comparison of radio frequencies. And we’re going to be doing that in relation to the isotropic radiator, which is again what sends the power into the antenna. So you’re going to see this term “DBI,” and then we’re also going to talk about the decibels as they relate to what they call a half-wave dipole antenna, which are the DVDs. And yes, there are some other decibel types of acronyms that you’re going to run into, but I hope by the time we’re done with this, they’ll all make sense to you.