Fundamentals of RF

11. Frequency Part2

So just graphically looking at the idea of these frequencies when we're measuring time, as you can see, from zero to 1 second, as it says here, how many times do we see the peaks in that time represent the frequency? And at a high frequency, that means simply that we see that event occur more often in that one time slot versus the lower frequency, where we see the peaks occurring less often.

12. Amplitude

Amplitude is what we would call the strength or power of a signal. If you were to use something like an oscilloscope,you would be able to measure the amplitude because the amplitude is basically represented by the positive crest and the negative troughs of the sine wave. And really, if we look at it from this centre line, the height of that signal would indicate that it has a strong or weak amplitude, depending on how we're measuring it. So to be stronger, that distance would be greater than it would be down here on a lower amplitude. Now, the amplitude, and we'll get into some of the ideas behind this, is an important aspect because, like I mentioned, with some of these communications, like microwave communications, they would not have as much power. And so, fortunately for us, that means they don't cause us, that we know of anyway, any significant harm. But when we get more and more power, more amplitude, then that wave could become dangerous again. I think about the microwave oven, and if you wonder why the glass front door has got that little cage on there, it's because we're trying to make sure we keep the strength of that signal inside the microwave oven so it doesn't cook the poor person who put the TV dinner in the microwave oven.

13. Phase Part1

We talked about phase previously, and we're talking about a relationship between two or more signals that have the same frequency. And the phase involves, as I said before,the relationship between the position of the amplitudecrests and the troughs of the two waveforms. So if I had a signal that I generated, I know it's not very accurate in my drawing. But if I have this signal frequency and I say Okay, It started at zero degrees. And then that same frequency is transmitted again. In this case, If it was Let's say 90 degrees out of phase. We would hopefully see that this negative trough would hopefully not affect the positive trough because they're not really occurring at the same time. So, in fact, if I had, let me make another chart.

If I had that first signal and then had another one that is at a zero degree difference in phase, meaning another frequency, the same frequency, but a different transmission occurring at the same time because it also would follow that same path, you would actually see that they would boost each other. Of course, data communications would be horrible at this point, but you'd actually see that we'd almost combine them. And so we would have a higher amplitude because of the additional frequency at the same phase. The other one basically boosts the other one. So they're boosting each other as if they were 180 degrees out of phase. Let's see if I can try to do a better sine wave this time. So if we were 180 degrees out of phase, what you would see is that a second signal, at the same frequency, would occur. It's negative at the same time. This one is on a positive crest. As a result, both of those would effectively cancel each other out, or have the potential to do so. It does also depend on the amplitude of each of those transmissions.

14. Phase Part2

So, graphically A better picture than what I was showing you here is that if we looked at the main signal and had one that was in phase, meaning that they were complementing each other, then together we would see that they would basically amplify each of the two signals together.If you're 90 degrees out of phase,we don't see as many problems. The negative part of this really isn't affecting too badly the negative trough on the first signal. And if it's 180 degrees out of phase, as I said, when that positive peak occurs and we have that negative trough, they would basically cancel each other out.

15. RF Behaviors

So, as your radio frequency signal travels through the air and other types of media, it may behave differently, implying that these media or objects may affect the overall ability of that radio frequency signal to travel. It could even, in some cases, bend the signal. By the way, it doesn't mean we're changing the frequency, by the way.It just means that we're going to see some different behaviors. Now, some of the ones we're going to talk about are things like absorption, reflection, scattering,refraction, diffraction, the FSPL, the free space, pathloss, multipath, attenuation, and gain. These are behaviours that are important for us to understand, especially because when we get into the world of actually putting in something like your access points, knowing the location and what the environment is like will help you make decisions, good decisions, about where to place these different, basically, antennas, the access points.

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