as we said in this training block we will do our best to explain the basic elements of rf this presentation will teach you the most fundamental aspects of rf and where these aspects play fundamental roles we will start with an introduction on rf as such and will continue with its fundamental properties such as frequency and wavelength we'll explain the impressive electromagnetic spectrum the power that rf can have the unit decibel and the term bandwidth of rf applications we'll zoom into a part of the spectrum and show you some typical applications and finally try to impress you with the united states frequency allocation map to give you an idea of rf's ubiquity and importance what is rf that we spend so much of our time talking about it and even do business with rf stands for radio frequency rf is a form of energy in the modification of time dependent electronic and magnetic fields in short it's an electromagnetic wave which propagates readily in vacuum or rather space or in solid-state media like metal on a circuit board or through a coaxial cable or it can propagate out of an antenna into space in former times people talked about ether as a medium to carry electromagnetic waves however that notion was pretty much wrong it simply takes space our three-dimensional world to carry these types of waves we said rf is an electromagnetic wave to be a bit more specific only the wave frequencies between one megahertz and three gigahertz are generally called rf above 3 gigahertz up to 30 gigahertz we speak about microwaves higher frequencies between 30 and 300 gigahertz are termed millimeter waves as we will see later when we discuss the electromagnetic spectrum even higher frequencies manifest themselves as eg visible light or x-rays or as terahertz body scanners at the airport this slide will clarify the relation of the terms frequency and wavelength for our electromagnetic rf radiation imagine yourself as an observer on the beach the sea waves pass you by and you track the distance between them that's the wavelength then you start counting the numbers of waves passing by per minute say that would give you the frequency of the c waves per minute with our electromagnetic rf waves it's exactly the same the number of waves per second is the same as frequency and the distance between wave maxima is the actual wavelength if one wave passes each second this is known as one hertz very common to rf and microwave are the terms megahertz and gigahertz this is one million and one billion waves per second i. e the frequency equals one megahertz and one gigahertz respectively it's important to note that the speed of electromagnetic waves in vacuum is always the same regardless of its frequency the waves travel with the speed of light if the speed is constant this also means that higher frequency waves must have smaller wavelength to give you an idea your magnetron at home runs at 2. 45 gigahertz frequency which corresponds to a wavelength of about 12 centimeters the reciprocal relation between frequency and wavelength is also the fundamental reason that the techniques that engineers use will vary depending on the portion of the rf spectrum they are working with high frequency engineers design with components that tend to be smaller and lower frequency engineers tend to use physical components that are of larger size what you see here on this slide is a part of the electromagnetic spectrum visualized the table shows the frequency range between 10 to the power of 5 100 kilohertz and 10 to the power of 21 hertz which does not at all imply that it stops at either end it also relates frequency to other parameters like wavelength wave number ie waves per centimeter and electron volt i.
e the energy of the electromagnetic wave at a given frequency you should also note that as the frequency increases more to the right that the wavelength is dropping as we said before you can also see that the higher frequency waves are more energetic by referring to the electron volt scale please note the examples of real applications which are shown here as well on the left most of the signal transmission kind of applications electronics and on the right the light based applications or optics can be found along with frequency and wavelength power is another very important parameter to consider power is the measure of the energy per unit of time that the electromagnetic wave can deliver the more power in the wave the further the wave can be transmitted like for a broadcast signal or the more deeply a wave can penetrate like in certain medical applications more care must usually be given to systems that operate with more power it's important to understand power in a relative way the next slide shows how power and parameters in general can more easily be thought of in relative terms this slide requires a lot of explanation but will be key to understanding the material in the more advanced rf courses so it's important to really understand what's going on here this slide shows the math tricks and vocabulary used by the engineers if we go back to all of that forgotten math from our younger years we remember that instead of multiplying in the linear domain we can add things in the log domain remember this becomes very useful when numbers become very large or likewise very small and when many multiplications are required for instance it becomes much easier to add five two-digit numbers than to multiply five six-digit numbers this practice is common when figuring power gains and losses through long chains of components so engineers will always babble in terms of db dbm dbc etc to know how many db some property is we need to know how many zeros were added to the number in the linear math domain then to get the number of dbs we multiply by 10. for instance if a signal gets amplified and becomes a thousand times larger then three zeros were added to its value this 3 gets multiplied by 10 to get 30 db conversely if a signal becomes 1 millionth as big it became 10 to the negative 6th power as big and minus 6 times 10 is minus 60. so in db it got affected by minus 60 db some other nice db number facts to remember are that every doubling of something in the linear domain adds 3 db in the db domain also every time something gets cut in half in the linear domain it drops by 3 db or you add -3 db in the db domain likewise if an amplifier has a gain of 20 db it amplifies the signal power by a factor of 100 right this allows engineers to go through the gains and losses in a system in a very fast way by adding numbers that are easy to handle i know this sounds clumsy at first but after a few years it's easy to do math in the db domain and you become thankful for it you'll see how this is used in further presentations the bandwidth of a signal can be considered as the width of the spectral chunk that is being covered by the signal or by the system for instance an fm radio can receive waves between 88 and 108 megahertz the car receiver then has a 20 megahertz bandwidth the fm wave per radio station itself has a certain bandwidth as well which indicates how much information the wave can carry so your favorite fm station transmits a wave that is about 200 kilohertz wide the music only covers a chunk around 20 kilohertz wide so the engineers use the remaining frequency space in that 200 kilohertz to pack information onto the wave to help the transmission be more pure and to let your car navigation system know where not to go this same principle applies to all the rf and microwave applications and scales and complexity as the system needs become more stringent for example in highly complex third generation cellular environments system needs far exceed those of music transmission for fm this is why cellular bands operate over broader bandwidths and each transmission from the cell towers is more broadband than for fm transmission the ever increasing need for information transmission usually adds to the demands placed on the electronic components and is the source of many of the challenges for today's engineers and in fact fuels a large part of our hprf business this table shows a few frequency blocks used by most popular applications in general systems that demand larger transmission distance will tend to be granted lower frequency allocations that's because using lower frequencies has a physical advantage of having less degradation caused by obstacles you'll also see four ism bands called out these are bands that are free to use with certain maximum power limitations the industrial scientific and medical ism radio bands were originally reserved internationally for the use of rf electromagnetic fields for industrial scientific and medical purposes other than communications you will again recognize your magnetron's frequency as an ism band together with your wlan in general communications equipment must accept any interference generated by ism equipment the bands and applications up to 3.
