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Need advice

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epilot said:
Yes the pic is taken from my digital scope it has a spectrum analyser too and I have seen to FFT of the wave too

the below are the time domin and FFT of the wave at 500uS

Are you sure that the upper level of the wave is not the upper sideband as I have assumed in the papers:?**broken link removed**

yes I meant 'see', sorry for mistype. what YUK means?!
Upper and Lower do not refer to the voltage levels on the scope. They refer to the mathematical values Fc-Fmod (lower) and Fc+Fmod (upper). As others have said, you can't see sidebands in the time domain - only in the frequency domain.
 
Nigel Goodwin said:
Yes, it's NOT the upper sideband, it's just a VERY highly distorted attempt at AM modulation - in fact, it looks like it's been rectified?.

Well, the whole circuit was made of a 4066 Quad Bilateral Switch IC and 3 resistors. when I was not able to see the lower part of the wave then I thought perhaps I lost the lower sideband, although do not know what is lost yet(an envelope?!)?
 
Ron H said:
Upper and Lower do not refer to the voltage levels on the scope. They refer to the mathematical values Fc-Fmod (lower) and Fc+Fmod (upper). As others have said, you can't see sidebands in the time domain - only in the frequency domain.

But perhaps can refer to the time!?

I am using a sine wave as modulating signal so why the FFT shows several spikes rather than just 3? I am not able to make a guess about that harmonics?
 
epilot said:
what YUK means?!

Yuk is an expression of disgust.

If you were to try and eat some food which had gone rotten, it would taste bad, you would spit it out and say "yuk, that is awfull!"
OK?

JimB
 
A few posts ago I wrote:

JimB said:
I am not sure I completely agree with RonH about what is in that trace, my first impression is YUK!.
JimB

Having given this a bit of thought, I now completely agree with RonH.
The problem which epilot has, is that he does not have any tuned circuits after his modulator to reject the base band (audio) signal which appears at the output along with wanted modulated HF signal.

JimB
 
JimB said:
Yuk is an expression of disgust.

If you were to try and eat some food which had gone rotten, it would taste bad, you would spit it out and say "yuk, that is awfull!"
OK?

JimB

Thanks Jim,
but according to my dictionary it must be 'YUCK'
 
JimB said:
A few posts ago I wrote:



Having given this a bit of thought, I now completely agree with RonH.
The problem which epilot has, is that he does not have any tuned circuits after his modulator to reject the base band (audio) signal which appears at the output along with wanted modulated HF signal.

JimB

OK, I'll post the current circuit and the tuned section (ie the baseband filter) which want to make today.
 
The first pic is the circuit which I have and the second is what I want to modify.
 

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epilot said:
The first pic is the circuit which I have and the second is what I want to modify.
You have to select the Q for the filter depending on the bandwidth of your modulating signal.
 
Ron H said:
You have to select the Q for the filter depending on the bandwidth of your modulating signal.

Know I am reading about Q but it would be very good if you explain more about it.

the modulating signal would be the 20Khz of audio

by the way the circuit uses a 12V single ended.
 
Are you saying that you want to modulate 40kHz with as high as 20kHz? I seem to recall you are trying to use single sideband. I'll guarantee you won't get double sideband, because your lower sideband is the same frequency as your carrier, which you are trying to filter out. I can show you how to use the 4066 and a couple of op amps to get balanced AM without the spurious modulating signal, but I'm not at all sure you will be able to use SSB or DSB with that wide percentage bandwidth. Demodulating the DSB signal would require synchronous demodulation (meaning you have access to the original carrier), and even that might be tricky A diode demodulator (detector) won't work. Demodulating SSB, of course, also requires access to the original carrier. I don't think "approximately the same frequency" is good enough in this situation.
Tell us again what you are trying to do.
 
We've been telling him this for most of last year Ron, he just doesn't listen!, also the bandwidth of the ultrasonic transducers is far too narrow for sending wideband audio.
 
Nigel Goodwin said:
We've been telling him this for most of last year Ron, he just doesn't listen!, also the bandwidth of the ultrasonic transducers is far too narrow for sending wideband audio.
At first I thought I was experiencing déjà vu, but then I remembered that I had actually read this before. I probably would not have spent so much time on the AM modulator discussion if I had realized where it was going!
Epilot, you remind me of Mstechca (who?).
 
Ron H said:
Are you saying that you want to modulate 40kHz with as high as 20kHz? I seem to recall you are trying to use single sideband. I'll guarantee you won't get double sideband, because your lower sideband is the same frequency as your carrier, which you are trying to filter out. I can show you how to use the 4066 and a couple of op amps to get balanced AM without the spurious modulating signal, but I'm not at all sure you will be able to use SSB or DSB with that wide percentage bandwidth. Demodulating the DSB signal would require synchronous demodulation (meaning you have access to the original carrier), and even that might be tricky A diode demodulator (detector) won't work. Demodulating SSB, of course, also requires access to the original carrier. I don't think "approximately the same frequency" is good enough in this situation.
Tell us again what you are trying to do.

Thanks Ron,
No I have no intention to generate SSB via this circuit. You can see that I mentioned the storry of 4066 in this thread, that means I want to inspect the storry of bandwidth and sidebands here.
The circuit seems very simple and the waveforms are very clear so I want to make several tests with the circuit.
Surely I have no INTENTION to demodulate anything at the moment, just try to learn modulation.
 
Nigel Goodwin said:
We've been telling him this for most of last year Ron, he just doesn't listen!, also the bandwidth of the ultrasonic transducers is far too narrow for sending wideband audio.

Nigel,
I don't want to send anything by any ultrasonic transducer.
If you are suspect just becuase I am saying '40KHz' carrier, I must say that I have no tenacity fot that freq, the reason is that I have an oscillator which was made to work at that freq for another projecy and I am using it for this test too (Sorry Don't have a function generator).
 
If you're just wanting to learn about modulation you still need a higher frequency - or only very low modulating frequencies. How about posting the circuit that generated that bizarre waveform?.
 
Ron H said:
At first I thought I was experiencing déjà vu, but then I remembered that I had actually read this before. I probably would not have spent so much time on the AM modulator discussion if I had realized where it was going!
Epilot, you remind me of Mstechca (who?).

Well, are you sure I am like him?:
https://www.electro-tech-online.com/threads/bye.21562/

Are you sure I am asking the same questions?
Are you think that this thread is just like my other threads in the field?

My math is not so good so I have alot of problems to understand the modulation (yes I have read several papers about that). So different questions come in my brain and I'll try to find the answer with trial and error and asking different question, but I am sure the time will solve the problem.
Plesae pardon me for any annoyance.
 
Nigel Goodwin said:
If you're just wanting to learn about modulation you still need a higher frequency - or only very low modulating frequencies. How about posting the circuit that generated that bizarre waveform?.

The oscillator?
 
epilot said:
Well, are you sure I am like him?:
https://www.electro-tech-online.com/threads/bye.21562/

Are you sure I am asking the same questions?
Are you think that this thread is just like my other threads in the field?

My math is not so good so I have alot of problems to understand the modulation (yes I have read several papers about that). So different questions come in my brain and I'll try to find the answer with trial and error and asking different question, but I am sure the time will solve the problem.
Plesae pardon me for any annoyance.
No, I'm not saying you're like him. I said you reminded me of him. That was when I came to the apparently erroneous conclusion that you were still pursuing wideband modulation of an ultrasonic transducer. I apologize. :eek: You are certainly not irritating like he was.

Nigel, he did post the schematic yesterday.
 
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