AM Detector Demodulator

[@AllAmericanFiveRadio]

Harvey The basics are so very important. And it is a good idea to to do the same subject again, and it is always a little different. I took basic electronics because of requirements a least seven times. After the third time and I had to take it for the fourth time I thought why. After the fifth time, I realized I learned something each time. KZbin, man do I wish I had this in high school. This new stuff is awesome. I wrote two books pictures, illustrations and text, all me. Just amazing stuff.

[@MrHarveyluke]

Richard, I always enjoy your videos which teach us the basics of radio. Even though I have been a ham for 44 years, and I know most of this stuff, it's always good to see a good presentation of the basics. Wish we had KZbin in the 60's! 73, Harvey, KM4JA

[@ricktighe191]

Excellent series of videos. Preserves the past for the future. Well done!

[@AllAmericanFiveRadio]

Thank you.

[@AllAmericanFiveRadio]

Thank you, and your welcome.

[@AllAmericanFiveRadio]

Thanks AndyDaviesByTheSea Hey Andy, Thanks again. I am happy with the response and surprised too. My KZbin Video List keep growing so I won't run out of ideas for videos. I thinks all this new technology is fantastic, and the applications are amazing. All the stuff you can do today really is remarkable. Three years ago I did not know if anyone would be interested. But it keeps growing. Regards, Rick

[@terryblackman6217]

Extremely well put. Thank you for sharing your experience with others.

[@AllAmericanFiveRadio]

Thank you, and your welcome.

[@AllAmericanFiveRadio]

Thanks 78recordrepair Because of the RC time constant of the 3MEG and the 0.1MFD it captures or stores the DC negative potential of the negative DC audio from the detector circuit. Those two parts were chosen so that the negative voltage on the grids of the first two tube would not change to fast or slow. If you did not have the radio tuned to a station the discharge path for the 0.1MFD is through the 3MEG and the Volume control to ground.

[@barn5923]

I love it, You make a grate Teacher , I wish you had been my Teacher in School. Thanks Darryl

[@AndyDaviesByTheSea]

Hi Rick, another really elegant explanation, I think your calm and considered delivery is excellent. Looking at the comments you're getting you're having a huge impact on your viewers, you've got me held when you're telling me what I already know, you do it so well. What a wonderful use of KZbin, to share useful experience and knowledge around the world and what a wonderful contribution to have made, Well Done! Kind Regards....Andy gw0jxm

[@AllAmericanFiveRadio]

Thanks CameramanLink Hey Bryan, I hope you are working on some projects. I think the reason why a diode can be a detector, is the most interesting part. Rick.

[@tunicana]

thank you allamericanfiveradio your vids are very instructive and helped me a lot to understand a lot of stuff in electrical engineering...

[@AllAmericanFiveRadio]

@CameramanLink Lasers are real interesting. Of course AM modulation is good, but I bet the frequence limit is much higher. The FM transmitter work really well. For stability it must be built as small as possible. It is amazing how far some KZbinrs have peeked it up, using an outside antenna.

[@togst]

Really great video, as always! I were not aware that the negative audio signal also could control the amplification. Very simple, yet ingenious idea! Best regards, Frank

[@fleminggp]

Thank you so much ... I have a much greater understanding now - Paul

[@AllAmericanFiveRadio]

Thanks togst Hey Frank, Some radios put in some kind of strength indicator too. The more negative, the stronger the station. Regards, Rick

[@tunicana]

thank you for this tutorial can you please show as how the capacitor separate the high and the low frequencies?

[@TDDMS]

I got your reply from your video you made today. Now I understand the difference between a demodulator and discriminator. So basically the LC or tank circuit is functioning as a band stop or notch filter to remove the carrier frequency?

[@AllAmericanFiveRadio]

Thank tunicana I did do a video on this a few years ago, don't remember the name, but I'll be glad the do another one. I'm sure the first one is not HD and I have better tools now.

[@whrgeorge]

Hi, I really like the way you teach. I got a question about it, so how capacitor can drain off those green part of signal ? thanks

[@franksmith4078]

great information, you make it easy!

[@allradio2]

Why did the demodulated and filtered negative audio signal end up with half the audio signal going positive again (you showed the 0 line through the center)? Thank You, Rich

[@AllAmericanFiveRadio]

+allradio2 The negative half of the audio modulated 455 Hz is chosen because of the automatic volume control circuit. You can do a channel search on my channel for 'automatic volume control'. After the 455 Hz is removed from the audio information, the only thing that will get amplified is the audio and at this point it does have a positive and negative component. So another words the audio modulated 455 Hz information is on the edge, the up-and-down part, when the 455 Hz is removed all you're left with is the audio, the up-and-down part.

[@AllAmericanFiveRadio]

+allradio2 On the oscilloscope screen there is a horizontal centerline and that represents the zero point. Anything above is positive anything below is negative.

[@vladan_kovacevic]

To get pure AC signal (which goes positive and negative) from pulsating DC (in this case it was on the negative side) you just put capacitor in series which blocks DC component of the signal, and only leaves you with AC which is what your speaker likes. So short answer would be: "Capacitor in series".

[@hunt555fish]

Great job as always Rick. Ron KA3WEL

[@AllAmericanFiveRadio]

Thanks MrHarveyluke 73, Rick

[@Kennynva]

Can you hook one channel thru the scope to see the audio and one to the other channel to see the carrier at the same time??

[@s.m.ehsanulamin7235]

I made a demulator detector but while checking the output I was getting both positive and negative values of the signal. After that I used a parallel 100kohm resistor with the input of demodulator. Then I was getting the modulated positive signal. My question is why I had to use this 100kohm resistor?

[@AllAmericanFiveRadio]

To complete the circuit

[@mcbublick]

great video! thanks!

[@AllAmericanFiveRadio]

Thanks raddios2

[@kurchak]

I understand that the carrier is taken way and the audio signal remains, but how? If we remove the carrier, and the audio signal was merely a representation of the amplitude of that carrier, then how are we left with the audio signal once the carrier is removed? Another way to say my question is, if we remove the carrier, isn't it's amplitude removed too? If so, how do we still have n audio signal? Considering the fact that AM radio works, I know that I am certainly missing something. Can anyone help with this? Thank you! Excellent video btw. ☺️

[@AllAmericanFiveRadio]

I have done a number of demodulation videos. The link below is the latest. Looking at the wiring diagram in this video C8A does drain off most of the RF. Remembering that AC will pass through a capacitor and DC is blocked. This is why the audio is left and the RF is gone. The complete RF filter consists of C8A, R3, and C9. These three components make up an RF Pi filter. Hope this video helps. How the Volume Control works in a All American Five Radio kzbin.info/www/bejne/qajLh3ljrMeSm68

[@kurchak]

@@AllAmericanFiveRadio I think it finally just clicked. So, the audio signal is captured by the charge/discharge of the capacitors, right? It's the AMPLITUDE of the carrier wave that determines how charged the caps are, and as they discharge between each carrier wave period that level will always be close to what the amplitude of the carrier wave was during that individual period. But since the caps are set up to only capture lower frequencies the carrier wave itself doesn't make it through, only the modulation, or amplitude of the carrier. Is this correct?

[@AllAmericanFiveRadio]

@@kurchak Capacitors blocks DC. The value of the capacitor determines the AC frequencies that can pass through it. Here are some videos that may help. Capacitors, DC, AC, and Frequencies kzbin.info/www/bejne/j5etfIGJoN-Sgs0 Capacitors, DC and AC Current kzbin.info/www/bejne/hHrRpWSJqJiph5Y Wire, Resistor, Capacitor, Coil, DC AC Characteristics kzbin.info/www/bejne/o3rJe6GMqqZrgKs Audio Coupling Capacitor, how it Functions in a Circuit kzbin.info/www/bejne/hnKzn6qOa76cf68 Oscillators, the Basic Tank Circuit 1 kzbin.info/www/bejne/nIKXqoWMet-Lh6M How Capacitors charge and discharge kzbin.info/www/bejne/d5iVg6ighK2kgJo

[@OIE82]

@@kurchak Capacitors PASS AC. Alternating (as in positive and negative relative to ground) Current. After the diode, only the negative half of the signal and carrier remains. And it is always negative. The signal gets more and less negative but always stays negative so the capacitor lets all of it through. But the negative part of the carrier doesn't go through because the 200 pF cap bleeds it off. The size of that cap is important to that frequency. If you slowly increase the size you would see that it would start letting more and more of the carrier through. Hope that helps.

[@AllAmericanFiveRadio]

Thanks UmaBlinky

[@rob_scooter6199]

thank you.👍

[@AllAmericanFiveRadio]

Thank you, and your welcome.

[@AllAmericanFiveRadio]

Thanks mcbublick

[@AllAmericanFiveRadio]

Thanks MEverett98

[@AllAmericanFiveRadio]

Thanks hunt555fish

[@javierbiaggi3072]

Great!

[@AllAmericanFiveRadio]

Thanks

[@AllAmericanFiveRadio]

Thanks vener6

[@AllAmericanFiveRadio]

Thanks tunicana

[@AllAmericanFiveRadio]

Thanks barn5923

[@brento2890]

Pico Fared is my name. Cool.

[@AllAmericanFiveRadio]

Thanks! Your welcome.