شرح مبسط لعمل الاتصالات اللاسلكية وموجات الراديو

how many of us really understand what goes on when you text your friend across the ocean and they get the ping almost

instantaneously allow me to entertain you with a little thought experiment when you press send on your favorite

messaging app where is your message really going into the air you'd say like radio waves but let's back up a bit when

you press send on a messaging app such as what's that you're essentially sending instructions to your mobile

processor via tiny copper wires on a printed circuit board inside your smartphone now these instructions are

essentially electrical impulses right and electrical impulses are just electrons flowing along the potential

difference how exactly does your message jump into thin air from being electron flows and copper wires at one stage you

had a circuit board that you could touch and feel and even smell and then suddenly you have radio waves in the

invisible part of the spectrum flying away into thin air at incredible speeds what's in between well an odd-looking

device it's an antenna which roughly translates to a pole in Latin an antenna is a metal tongue wudu device that

swallows when pulses and spits out radio waves it's as silent as the dead but it's screams can be heard for miles

specifically a Wi-Fi antenna like the one here in the picture screams that 2.4 gigahertz that's more than 2 billion

beats per second and spits out waves of roughly 12 and a half centimeters in length

unlike visible light these waves can pass through certain materials and even bend around corners but how does an

antenna produce radio waves before we answer this question let's take a small detour to remember the reason buzz in

pop science about gravitational waves the basically fluctuations in gravitational field propagating as

radiant energy Einstein's general relativity predicted their existence many years ago and we've only recently

discovered them just like gravitational waves electromagnetic waves are fluctuations in an electromagnetic field

propagating as radiant energy and not much unlike the story of gravitational waves the existence of invisible

electromagnetic waves was predicted by Maxwell's equation well before their discovery by Heinrich

her so to produce radio waves you need to create fluctuations in the electromagnetic field and to create

those fluctuations you need electrons moving around in a conductor the act of radio waves synthesis is a carefully

choreographed rhythmic dance of electrons and tiny copper wires like perturbations in stillwater that radiate

outward from the point of disturbance the electron flows in an antenna caused perturbations in the electromagnetic

field which radiates out into space as electromagnetic waves when you press send

on your favorite messaging app your mobile operating system sets off a chain of events that ultimately encodes the

message as a carefully choreographed electron dance the stan's results in rhythmic herbs and flows in the

electromagnetic field in the surrounding space which radiates outwards towards a cell tower the receiving antenna on the

cell tower feels these ABS and flows on its conducting surface inducing an electron dance very similar to the one

from the transmitter this electron dance is again a set of electric impulses in tiny copper wires which are decoded by

the hardware at the cell tower the decoded information is then carried on high-throughput cables for thousands of

miles across countries continents and even oceans through transatlantic communication cables or some other

submarine communication cables to a cell tower near your friend across the ocean from the tower to your friends phone is

another Wireless jump and finally your friend hears the familiar ping how does the phone know where the cell tower is

it doesn't and it doesn't need to your phone broadcasts your message in all directions for anyone to listen to but

don't worry your message will be encrypted and only the cell tower can decode your message how does a cell

tower know that the message is from me I hear you ask with every message you transmit you also include a code that

uniquely identifies your device that is how the cell tower knows that it's you but how does the cell tower

differentiate between messages from different phones the phones all agree on a protocol to send messages to the tower

at either different times different frequencies different locations or using different codes the best analogy I have

for this is that of a classroom imagine it contains 100 students and just one teacher now if all the students starts

get once the teacher cannot understand any of them so they agree in a protocol if a student wants to speak they race

their hand and wait for the teacher to point to them if multiple students raise their hand at once the teacher picks

them out one by one so that only one student is speaking at any given time in this case the cell tower is the teacher

and the devices are the students while students can speak at different times to avoid interference devices can speak at

different times different frequencies or different codes to avoid interference so you're telling me that the majority of

the communication is not really wireless yes unless you're using a satellite phone wireless communication is only

used for two steps along the road sender to tower one and tower two to receiver the communication between the cell

towers happens through ultra-high speed communication cables underground but aren't cables so out of fashion for the

21st century why not use wireless all the way well the cables were talking about here like the transatlantic

communication cables are definitely very high-tech that can carry terabytes of data every second and do not face the

problem of interference nearly as much as their wireless counterpart also you'll need a lot of satellites to cater

to billions of users and their data needs if you want to go wireless all the way and launching satellites is a very

expensive process that's it for this episode of tell me why go ahead and check out our other interesting videos

if you're free to subscribe if you haven't done so yet until then stay happy and stay curious

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