Now let's start with the physics what is wireless essentially wireless is a term we're using for electromagnetic waves electromagnetic fields that travel in space and time these waves they have a frequency they have a wavelength and they have a speed with which they travel the speed we're typically calling the speed of light because light is also just one of these electromagnetic waves and that speed of light is very very fast it's three times ten to the eighth meter per second if you want to memorize this you can think a foot a third of a meter in a nanosecond as a rule of thumb the wavelength often called lambda and that's something we measure in meters or centimeters and millimeters that's coupled to the frequency so it's different from frequency to frequency and we'll be looking at some of those and the frequency is the number of oscillations in a second and we call that a hertz so when we're saying something has an oscillation of frequency of 1000 hertz it would mean it oscillates it swings 1000 times in one second and the two things the wavelength and the frequency are coupled together their product makes the speed of light i think you can imagine that when you think this is the length of this wave and this is how often it moves per time then you put these two things together and you have the the speed with which it moves so and to give you some examples of frequencies that we'll be uh using that we'll be looking at in particular wi-fi frequencies such as 2.4 gigahertz 2.4 times 10 to the 9th hertz or 5 point something gigahertz and these have wavelengths of respectively 12 centimeters and around 6 centimeters depending on the exact frequency electromagnetic waves are a little bit difficult to understand they're different from mechanical waves that we know mechanical waves such as sound imagine when you're playing a guitar or you're beating a drum then there is an object that vibrates that moves the guitar string the skin of the drum when sound travels from that instrument to our ears it actually does so carried by the air molecules that go into some form of vibration so these mechanical waves they have a medium that carries them and the guitar string the skin of the drum the air molecules electromagnetic waves don't have any such bearing medium and they can travel through nothing through vacuum they can also travel through air but they don't need the air to to carry them um they can go through some materials more or less good and we'll look at that in more detail but the important point here is it is not the medium that carries them they are traveling through nothing i sometimes like to say they're a dance without a dancer we can identify a traveling form of energy but we can't say this is the thing the matter that actually carries that energy the energy is carried by nothing the energy is traveling through nothing examples of electromagnetic waves i've named a few already light x-ray radar mobile networks wi-fi networks all of these are electromagnetic waves let's look at the spectrum of this spectrum is the term for showing all the different frequencies here left to right from low frequencies to higher frequencies and in this picture in the low end we see different forms of radio am fm radio then followed by cell phones wi-fi microwave ovens live here further up we'll be having first infrared warmth radiation infrared is the carrier of what we perceive as warming radiation as the frequencies get higher the wavelength shorter we will be having visible light that's probably the form of electromagnetic radiation that we know the best because we see it it's only a tiny part of the electromagnetic spectrum though and then on top of that comes ultraviolet uv and if we go even further up we get ionizing radiation radioactive electromagnetic radiation powerful enough to actually crack electrons out of atoms and molecules to crack molecules and damage living matter in particular so this is the very very high energy electromagnetic radiation the terms we're using and i've used them already i've said wireless i've said radio they can be a little bit complicated and confusing radio is a term that's used for typically everything from 30 hertz to 300 gigahertz microwave little bit narrower is a term we're typically using from 300 megahertz to 300 gigahertz and then you have terms like vhf very high frequency 30 megahertz to 300 megahertz and an ultra high frequency 300 megahertz to three gigahertz now these terms obviously are historically grown first we set very high then that wasn't high enough and we said ultra high frequency since it can be confusing let's remember we can con we can call all of these radio without making the mistake we may summarize these all as radio so i'll be talking of radio in general here for the frequencies and the radiation that we're using for wireless for mobile phones and so forth.

© Produced by Philip Smith and the Network Startup Resource Center, through the University of Oregon.

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