AM Modulation and Demodulation (Edited)

This video uses properties of the Fourier transform to explain modulation and demodulation inside a simple AM radio system.
This video was created to support EGR 433:Transforms & Systems Modeling at Arizona State University. Links to other videos can be found at www.engineeringvideos.org and sites.google.com/a/asu.edu/sig...
This video is made available under the Creative Commons BY-SA license.

[@Eng1neering]

Darryl, you are the king of signal and systems on youtube.

[@GabrielaRodB]

Now I got what my teacher was trying to teach me the whole semester! Thank you.

[@MoeSalamaIbrahim]

I'm still a high school student and I understand signals !!! Good Job Professor, keep it up ^_^

[@timothytong9169]

Absolute gem, thanks so much for the video!!

[@danieltong7900]

Very clear and detailed explanation ! thank you !

[@NarasimhaMurthyV]

Thank you very much. This is a great video on AM.

[@erin19030]

Everybody is an expert now!

[@teakodo]

thank you for sharing your knowledge

[@DarrylMorrell]

Multiplying the baseband signal (m(t) + 1) by cos omega_c t generates the sidebands. Multiplication in the time domain becomes convolution in the frequency domain. In the frequency domain, the cos waveform is two delta functions at -omega_c and omega_c. Convolving the Fourier domain information signal with a delta function shifts it to the frequency of the delta function, so the information signal ends up centered at -omega_c and omega_c.

[@maziarghorbani]

Great video, thanks

[@tvrteja8837]

Thank you for the video

[@muddassirghoorun4322]

Thanks a lot! Perfect!

[@robwasab]

@shiva prasad, I think you add 1 to m(t) so that you can correctly envelope the cos function. If m(t) isn't entirely positive, then the cos function will not be enveloped by the original m(t), it'll be something else, not reflected about the time axis.

[@jenko701]

Your radio graphic is is a fm radio , this is fine ,but as detailed as your video is you should have explained why AM only radios never have an antenna like on your radio. This would be a good way to express characteristic wavelengths of AM, and let your students have an introduction to antennas . This will give insight when just looking at an antenna what it’s designed for. Great video.

[@MohamedElsheikh22]

Awesome :) TY

[@tamyboy1]

love it

[@samchow10]

thanks for your videos. I was wondering if you knew a video explaining the effect of the mixer being cos((w_lo * t) + 90 degrees) . maybe yours does and I am just not catching it.

[@milestopping123]

This is great! Do you also do an FM video?

[@iipvidyaniketan1074]

lovelyyyyyyyyyyyyyyyyyyy..thanks sir jii....

[@chamaraweerasinghe3909]

thanks

[@slap_my_hand]

I should probably look up what a fourier transform is before watching this.

[@DarrylMorrell]

I have taught introductory communications courses, but do not consider myself knowledgeable enough to be a telecom engineer.

[@MexterO123]

I'd don't see how adding one will make a signal all throughout positive. I mean what if you had a signal that goes all the way down to -2 wouldn't the the signal still be negative if you add one to it.

[@FersotJ]

+Memo “MekoxTwiSparkle” Pony He said that the signal has to have amplitude ≤ 1. In general, you would just have to shift it by a, but 1 makes the math easier.

[@okami11408]

Are you telecom engineer?

[@shivaprasadbebetterthanthebest]

why did you add +1 to m(t)

[@joeldjiogo7888]

Hi man, if we even forget about the fact that we are doing AM modulation, a DC signal added to an AC signal just lifts the signal up or down in the y axis. Now in this AM modulation case, we want to lift that signal up away from the third and forth quadrant meaning negative below zero. It makes the modulation super easier to do besides the fact that it is a way to encode, a way to prevent loss of power during transmission of the signal more. etc hopefully it helps and not confuse you more.