Telecommunications - A Level Physics

A description of telecommunications: AM and FM; use of carrier waves; analog and digital signals; broadcast options; satellite transmission; gain and attenuation; PSTN; mobile/cell phones and networks.

[@DrPhysicsA]

All the relevant waves are electromagnetic waves. Sound waves are converted. Carrier waves are generated either in the phone or the transmitter (depending on which way the information is flowing). The carrier wave is an EM wave which has the characteristic of being able to travel sufficient distances (usually in the microwave region). The sound wave which is converted to an EM wave is then embedded in the carrier wave. Once it reaches its destination the carrier wave is stripped off.

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[@DrPhysicsA]

One way of doing it is Frequency Division Multiple Access (FDMA) : FDMA separates the spectrum into distinct voice channels by splitting it into uniform chunks of bandwidth. Each call sends its signal at a different frequency within the available band per geographical cell. But there are other ways with digital communications. Wikieducator has a good pdf piece on cell phone technology.

[@bushraimtiaz3723]

Really informative. Thank you so much

[@manahilkhan2555]

OMG. NOW I UNDERSTAND THIS WHOLE TOPIC. THANKYOU SO MUCH! LOTS OF LOVE

[@LarsBerntzon]

Very nice video covering a lot of good information. I detail: the AM modulation you are drawing is not quite like that in normal AM, what you have drawn is side band modulation where no effect is transmitted when the modulation signal is 0 v. With normal AM, the carrier voltage is half its max when modulation signal is at 0 V.

[@linkchibi]

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[@noctavel]

If the power of a mobile is so low, how can be possible for an receiver to get the signal from a mobile phone? can you make a video about it ? Thanks !!

[@etiennesilvio]

1000 Thanks for this video.!

[@krishan]

Hi i just don't quite get the bit about bandwidth, how come if you reduce the bandwidth leading to higher frequencies lost, that will reduce the quality of transmitted signal?

[@Alfster18]

Great video, thank you! What do you mean when you talk about the bandwidth of the AM wave because you say that the amplitude is 20kHz but I thought amplitude was measured as a distance?

[@sohaibabbasi3355]

9:35 i think you mean frequency of the wave

[@DrPhysicsA]

If you embed a signal within a carrier wave then there is a degree of uncertainty about the precise wavelength of the carrier wave. That uncertainty is really the bandwidth. It is the amount of the spectrum that is taken up to cover all the frequencies needed to be included in the signal such that there will be no interference with the signal embedded in a neighbouring carrier away

[@zainabm9650]

please tell me from where the carrier waves are transmitted??from a radio station?and how does the information signal attatch on the radio carrier waves??and the informaton signal refers to the sound waves??

[@spdandavate123]

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[@timmytim9054]

1:18 “coil of WAAAAAH”

[@anayparikh3198]

WAAAAIAAAAA

[@gpsinghgajju]

Hello, why does signal from one mobile does not interfere with another mobile close by, thanks.

[@geoffreyengatkinson]

10 million thanks for this video

[@saadawan8283]

Nice work.

[@Antropovich]

Is it really how ADC works? I mean to represent a wave with a certain amplitude in analog, it takes several waves to represent the same wave in digital... Which is the reason "you loose information density by converting from analog to digital"... Or am I missing something? I am referring to 16:50

[@moshecohen-mn9cj]

you are the best +DrPhysicsA

[@roykharal5978]

well explained lectures

[@Ashique4241532]

Thank you SO SO SO much!!!

[@zatulmutalif3230]

sir what is bandwidth?? i dont really understand part 09:20...thank u:)

[@alexchen2519]

Im still not sure why the frequency of the signal is added to the frequency of the carrier wave. I thought AM has no effect on the frequency?

[@mauthoormotasim6332]

exactly mate. I don't understand too.

[@crossvizannuff]

Sir, thankyou very much!

[@OMAIMHREEM]

Thank you Sir for the wonderful you tube. please give me detail explanation how is Microwave auditory effect this is what I mean microwave hearing, is modulated using satellite.

[@Jayce1712]

Thank you very much sir, you are a-w-e-s-o-m-e :)

[@mohamedmahmoud-ze9sx]

that was so helpful, thank you :)

[@ervinkiller]

thank you very much.

[@fenghc1]

The ADC part: x axis should be time other than frequency. Am I right?

[@pindiboii7247]

no its at a particular instant of time so time is constant

[@mahmoudm451]

at 9:00 what do you mean by "the amplitude is 20KHz" ? how is the amplitude measured in Hz?

[@hadiyousef1704]

He means to say the frequency is 20 kHz, just a silly mistake. well done for catching onto that!

[@fareedaappa2327]

wonderful

[@ashazwar6794]

what to do mean around 14:30 by 200khz=15khz?

[@DrPhysicsA]

At 13:30 i say that FM equates to (rather than equals)

[@zawaideh61]

hey sir, can you please do video on the attenuation per unit length of the signal??

[@learnwithuziharry7035]

A level physics?

[@ArthurZH]

The question now is why is there a bandwidth for AM. If I am merely manipulating my carrier wave's amplitude with respect to the signal, it's frequency should remain unchanged, right? Or am I getting something wrong here?

[@lazeran]

In combining the signal with the carrier you produce two side-bands, one on each side of the carrier.

[@alexchen2519]

Yes but WHYYYY?

[@shifamuhammad7366]

I’m confused about this too! Can someone please please please explain this

[@jacobvandijk6525]

Is the carrier-wave digitalized too (before transmission)? And how does a digital signal move the electrons in the antenna (to create the EM-radiation)?

[@DrPhysicsA]

No. The carrier wave is just a straightforward Electromagnetic wave in the microwave region or radio wave region. There is no signal in it to digitise until you add the signal itself either in analog or digital form.

[@jacobvandijk6525]

DrPhysicsA Okay, thanks!

[@shockingvideos5225]

DrPhysicsA how varying voltage is applied?

[@jacobvandijk6525]

Animation The difficulty is that a lot of the time there is talk about waves, where in fact it's just signal-processing. The only real waves are the incoming soundwave and the outgoing radiowave; inbetween there is no wave.

[@khizeriftikhar9157]

Thanks again 😃

[@DrPhysicsA]

In an AM wave the carrier waves sine wave is itself modulated to carry the signal. The bandwidth is the degree of spread on the carrier wave.

[@bmodon6881]

Thank you very much i have physix=cs exam tomorrow and i think i doing it well!!!!!

[@DrPhysicsA]

All good wishes for the exam.

[@microwavecoffee]

THANK YOU

[@amroto97]

In the Cambridge A level endorsed book, it is log(P2/P1), which is opposite to what you have explained can anybody clarify this for me ?

[@esaskhan95]

amr ramadan yep that was a little confusing

[@zhen3356]

amr ramadan you're forgetting the fact that he took P2 as Pin and P1 as Pout

[@nriver38]

Sir, during your explanation of bandwidth, why did you use kilohertz as the unit of amplitude?

[@DrPhysicsA]

I was adopting too much of a shorthand. Amplitude is not measured in kilohertz.

[@Hammadmk971]

+DrPhysicsA what exactly were you referring to? Frequency or amplitude? I'm a little confused .-.

[@leonardowilhelmdicaprio999]

@@Hammadmk971 Frequency is measured in kilohertz.

[@3551Bashir]

definely a thumps up.

[@leonardowilhelmdicaprio999]

Thumbs, you mean?

[@adithyarathnayake9797]

Thank you

[@DrPhysicsA]

More accurate to say that it will reduce the quality of the embedded signal, that is the actual signal which contains the information about sound etc.

[@glaiver4ever]

well you basically mean 20KHz Frequency and not Amplitude of the info signal, right?

[@maazmunir9213]

Yes

[@adityanalwaya5502]

First of all thank you sir for this wonderful explanation of Telecommunication I have one doubt here that if you are telling that for sending message to far distance we have to modulate it at higher Frequency But On the other hand FM (Which operates at higher frequency) travels less distance as compared with AM (Which operates at lower frequency) Why is it so can you please clarify that???

[@DrPhysicsA]

Long wave radio waves will certainly travel further but are subject to greater interference. FM has a better quality.

[@madarajkc]

thanks :)

[@yuanhuilee3082]

When he said BALLOON at 1.36 i laughed

[@Sairam-ky2os]

its wrong the bandwidth of AM depends on frequency of signal not amplitude of signal which is volts music consists of many frequiences superposed

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[@bilalafzal1914]

How can we measure amplitude in kilohertz?

[@ItsCaydenOG]

+Bilal Afzal Its the number of complete cicles per second, and then you divide it by 1000

[@lazeran]

You can't. Amplitude is loudness, not cycles per second.

[@amir-the-great]

1 there full !!

[@842Mono]

Bishoy George Mohamed Yasser

[@ujjwalmehrotra3149]

9:20 you say amplitude is 20kHz . How can amplitude be in hertz> wtf

[@DrPhysicsA]

I think I probably meant to say frequency.

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