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Demodulation

vick5821

Jan 22, 2012
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Your question might win EP's 'Oddest Question Ever Asked' award. I'm not sure what you're asking. It only makes sense if your a student and want to know what your instructor might ask you about your project. As in: "Mr. Vick please explain the purpose of C1 to the class".

So, is this the general idea of what your asking?

Chris

Yes, I am asking about what type of question my instructor will ask ?? I need to prepare on how to answer them.

Thanks :)
 

CDRIVE

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Post the latest schematic that you're working from and we'll go through it.

Chris
 

CDRIVE

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This is my design :
http://www.google.com.my/imgres?img...lCgUaSdNIjqrQeK1oD4Dw&ved=0CDsQ9QEwAQ&dur=282

I am using this kind of envelope detector. Simple one but I nee to udnerstand all the concept that is necessary to face my instructor.

Thanks for the help ! :)

Well, the gentleman that authored those pages ....
Content and pages maintained by: Jim Lesurf ([email protected])
using TechWriter Pro and HTMLEdit on a StrongARM powered RISCOS machine.
University of St. Andrews, St Andrews, Fife KY16 9SS, Scotland.
was quite thorough and it's definitely a college level (math) treatise on the subject. So what concept has you quagmired? Since college level electronics is 95% math there's not a lot of real world nuts & bolts, hands on bench time. Do you need a more basic breakdown? Do you understand the theory of operation of a common AC to DC linear power supply? I ask because a basic Diode Detector (RF Demodulator) and a 1/2 wave power supply rectifier have much in common.

Chris
 

vick5821

Jan 22, 2012
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Well, I understand that. Hehehe.

So what you mean is I have to use the mathematical analysis to explain to my instructor ? Or most probably my instructor will ask about the math stuff ? I think basically he will ask me about the concept about the detector which I am not very sure what will be the questions now ><
 

CDRIVE

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Well, in that case this thread is going to veer off into "Home Work" territory. The mods may elect to move this thread to https://www.electronicspoint.com/electronics-homework-help-f106.html

I will supply you with schematics, plots and TOP as I walk you through it but I won't give you anything that can be repeated verbatim. When we're done you should have an understanding sufficient enough to give your own dissertation. The maths involved with what I give you will also be basic.


Chris
 

Harald Kapp

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When we're done you should have an understanding sufficient enough to give your own dissertation
Hey Chris,
I very much apppreciate and support your attitude. Maybe it won't suffice for a dissertation, but understanding how stuff works is always much better than rote learning.

Give a man a fish and you feed him for a day. Teach a man to fish and you feed him for a lifetime.
Chinese Proverb

Enjoy the party :cool:
And, Chris, remember: don't drink and post ;)
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
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Give a man a fish and you feed him for a day. Teach a man to fish and you feed him for a lifetime.
Chinese Proverb

In the case of some of our posters, I fear this is closer...

Give a man a fire and he's warm for a day, but set him on fire and he's warm for the rest of his life -- Terry Pratchett
 

CDRIVE

Hauling 10' pipe on a Trek Shift3
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Hey Chris,
I very much apppreciate and support your attitude. Maybe it won't suffice for a dissertation, but understanding how stuff works is always much better than rote learning.

Give a man a fish and you feed him for a day. Teach a man to fish and you feed him for a lifetime.
Chinese Proverb

Enjoy the party :cool:
And, Chris, remember: don't drink and post ;)

Ha Harald, I refrained from posting when I returned home. At least I think I did! :D

In the case of some of our posters, I fear this is closer...

Give a man a fire and he's warm for a day, but set him on fire and he's warm for the rest of his life -- Terry Pratchett

That's funny Steve!

Before I post anything for Vick I have to model a 1N34 but first I'm going for a long bike ride. The weather is a bit cooler and dryer today, so I'm hoping not to look like a wet rag sitting atop a bike. :)

Chris
 

dietermoreno

Dec 30, 2012
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This is my design :
http://www.google.com.my/imgres?img...lCgUaSdNIjqrQeK1oD4Dw&ved=0CDsQ9QEwAQ&dur=282

I am using this kind of envelope detector. Simple one but I nee to udnerstand all the concept that is necessary to face my instructor.

Thanks for the help ! :)

You don't need any mathematical analysis to understand how the diode envelope detector works.

edit by moderator --- removed incorrect info

How it works is that a voltage controlled oscillator at the transmitter takes the RF signal generated by an oscillator and the RF is amplitude modulated at audio frequencies.

The audio cancels itself out super imposed on top of the RF carrier wave, so a diode is needed to allow only half of the RF carrier wave with the super imposed audio to pass. Only half of the RF carrier wave with the super imposed audio passes so the audio signal remains and the RF carrier wave can not be heard by the human ear because its frequency is too high. Optionally, a 1,000pF capactor can be added to remove the rectified RF after the detector.

This is for amplitude modulation (AM)

Frequency modulation (FM) reception is also possible with no modification to the radio receiver (other than antenna design, small enough components with low capacitance and low inductance, and keeping the wire leads as short as possible) by using slope detection.
 
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vick5821

Jan 22, 2012
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You don't need any mathematical analysis to understand how the diode envelope detector works.

edit by moderator --- removed incorrect info

How it works is that a voltage controlled oscillator at the transmitter takes the RF signal generated by an oscillator and the RF is amplitude modulated at audio frequencies.

The audio cancels itself out super imposed on top of the RF carrier wave, so a diode is needed to allow only half of the RF carrier wave with the super imposed audio to pass. Only half of the RF carrier wave with the super imposed audio passes so the audio signal remains and the RF carrier wave can not be heard by the human ear because its frequency is too high. Optionally, a 1,000pF capactor can be added to remove the rectified RF after the detector.

This is for amplitude modulation (AM)

Frequency modulation (FM) reception is also possible with no modification to the radio receiver (other than antenna design, small enough components with low capacitance and low inductance, and keeping the wire leads as short as possible) by using slope detection.

Have a question here : http://forum.allaboutcircuits.com/showpost.php?p=613400&postcount=22

What is the relationship actually ?

Thanks !
 

dietermoreno

Dec 30, 2012
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Have a question here : http://forum.allaboutcircuits.com/showpost.php?p=613400&postcount=22

What is the relationship actually ?

Thanks !

Putting an RC circuit after the detector in a TFR (tuned frequency receiver) creates either a low pass or high pass filter depending on which way the capacitor is put, before or after the resistor load. There is no need for the resistor because the wires and the inductor offer DC resistance, thus putting a capacitor after the detector creates a low pass filter. The low pass filter is used in the TFR to remove the remaining half of the RF carrier wave after the detector.

An RC circuit is put before the detector in the super het (super heterodyne receiver) to remove the undesired beat frequencies.

I'm not sure what you were trying to ask about charging and discharging. Yes, a capacitor charges and discharges. A bigger capacitor can hold more charge, and how fast it discharges is determined by the resistive load. Say you have a water pump pumping water up into a bucket. The water pump is the battery which is pumping charge into the bucket. Say that the bucket is connected to a garden house at the bottom. The garden hose is the resistive load. The more coils, kinks, and length of the garden hose, the greater the resistive load and the longer it takes the water molecules or charge to drain from the bucket. The bigger the capacitor, the faster the discharge rate because there is more charge stored in the bucket that has a potential energy (voltage) that forces itself through the garden hose faster. The discharge rate is charge per second, which is electric current. However, the bigger the capacitor, the longer it takes for all charge to drain, which is why bigger capacitors are used in LC circuits at lower resonant frequencies.
 
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CDRIVE

Hauling 10' pipe on a Trek Shift3
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I'm sorry for the delay but I lost my DSL over the past 2 days and what I have now is sporadic. I have been working off-line on what I promised you though .

While I do have access I want to tell you that the only thing that dietermoreno will bring to this discussion will be absolute chaos! I will tell you flat out that I'm not happy that he injected himself in your topic. He can't even comprehend his own projects! Nothing useful can possibly come of his information. About 90% of his last post is gibberish.

Chris
 

CDRIVE

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If the Lord is willing and the Creek don't rise I'll be posting what I promised by this weekend.

Sorry for the delay.
Chris
 

CDRIVE

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I'm sorry for the delay but better late than never.

Let's start with this attachment. It shows an RF generator that is outputting a 500KHz Carrier, Amplitude Modulated by a 1KHz tone. The modulated carrier is then fed into a simple RF Detector (Demodulator), which is nothing more than a rectifier diode and load resistor. I chose RL=100K because I believe a crystal earphone will have an impedance approximating this. That said, RL can't be replaced by a crystal earphone because the diode requires a DC path, which a crystal earphone won't supply.

What are your questions regarding this circuit and plots? Are you clear regarding what a Modulation Envelope means?

Chris
 

Attachments

  • FIG1_RL=100K.JPG
    FIG1_RL=100K.JPG
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