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Thread: Resonance

  1. #1 Resonance 
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    Hi,

    i was walking through the park and then bang! it hit me. This question appeared: Can resonance be picked up by a receiver?


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    Brassica oleracea Strange's Avatar
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    I don't really know what you mean by resonance being picked up.

    Resonance just refers to the fact that some systems have a tendency to oscillate at particular frequencies. You can have acoustic resonance (this is how organ pipes or flutes work). You can have optical, mechanical, electrical and all sorts of other forms of resonance.

    What specifically are you thinking of?

    In terms of receiving signals, a radio receiver uses a tuned circuit that resonates at the frequency of the radio signal you want to pick up. That allows you to amplify that signal and ignore others. Is that the sort of thing you are thinking of?


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    Quote Originally Posted by Sci_Research View Post
    Hi,

    i was walking through the park and then bang! it hit me. This question appeared: Can resonance be picked up by a receiver?
    If by "receiver" you mean a radio receiver, then understand that radio receivers pick up electromagnetic waves. Resonance is often incidentally involved, because resonant circuits respond strongly to a narrow band of frequencies, and only weakly to others. That property confers selectivity to many types of radios (i.e., you pick up only the signals you want, and reject the rest).

    But radios don't pick up resonance; that makes no logical sense.

    ETA: I see that Strange types a lot faster than I do!
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    Well sort of. I was thinking more along the lines of something like this :

    Resonance caused by Frequency and amplification causes the frequency used to be received but because of the amplification applied (using a volume switch) the wave form changes.

    So with this in mind, i'm having difficulty in understanding :

    A) how can frequency change as well as the wave form it produces as you apply less or more current into the same frequency coil (Because you are only using one coil); and
    B) if the frequency that comes out of the output causes resonance, then the frequency used for that resonance would still be present wouldn't it?
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    Brassica oleracea Strange's Avatar
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    Quote Originally Posted by Sci_Research View Post
    Resonance caused by Frequency and amplification causes the frequency used to be received but because of the amplification applied (using a volume switch) the wave form changes.
    Frequency and amplification of what? Sound? Radio? Water waves? A pendulum?

    And in what way does the waveform change? If something is resonating then the frequency is, presumably, reasonably constant (by definition). If you are amplifying whatever-it-is then the amplitude will change.

    It is not at all clear what you are thinking of here.

    A) how can frequency change as well as the wave form it produces as you apply less or more current into the same frequency coil (Because you are only using one coil); and
    If you have a tuned circuit (typically a coil and a capacitor) then the frequency will not change. Are you asking how you can make the frequency change? That would require either the coil or the capacitor to be adjustable. If you look in an old radio you will see that the tuning knob adjusts a multi-vane capacitor to change the resonant frequency of the circuit.

    Of course, it is all done electronically nowadays, using digitally synthesized waveforms, and electronic filters, etc.

    B) if the frequency that comes out of the output causes resonance, then the frequency used for that resonance would still be present wouldn't it?
    Sorry, not sure what that means.
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    Quote Originally Posted by Strange View Post

    Frequency and amplification of what? Sound? Radio? Water waves? A pendulum?
    Various things, more preferably sound. What is a pendulum and how is it involved with amplification and frequency?


    And in what way does the waveform change? If something is resonating then the frequency is, presumably, reasonably constant (by definition). If you are amplifying whatever-it-is then the amplitude will change.
    Well think of it like this (from what i studied): the waveform changes from this 'wwwwwww' at e.i. 20 mhz to this WWWWWWWWWW at e.i. 120 khz. You see the waves get bigger? sometimes they do the 'DNA' waveform. I call it DNA because it looks like a DNA strand but not.


    If you have a tuned circuit (typically a coil and a capacitor) then the frequency will not change. Are you asking how you can make the frequency change? That would require either the coil or the capacitor to be adjustable. If you look in an old radio you will see that the tuning knob adjusts a multi-vane capacitor to change the resonant frequency of the circuit.
    Cool. Are you saying that if i attach a potentiometer to the coil or capacitor, i could change the amount of current produced to fit a desired frequency? But doesn't the frequency change as you apply the number of turns on a coil, thickness of a coil and the amount of current/voltage applied? Also i was thinking if there was one frequency and the amplification part were to change the amount of waves generated at that frequency, wouldn't that mean it's possible that a wave sent could be adjusted? What i mean by this is the amount of waves sent such as ------------- (rapid waves) and this _______________ _______________ ________________ (Long waves)
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    Quote Originally Posted by Sci_Research View Post
    What is a pendulum and how is it involved with amplification and frequency?
    A pendulum (or a swing) is a nice simple example of a resonant system. It has a characteristic frequency. If you give it a regular but small pushes at this frequency, the swing of the pendulum will gradually increase because it stores energy.

    But if you give it regular pushes at a different frequency this will either have no effect or cause it to lose energy.

    Well think of it like this (from what i studied): the waveform changes from this 'wwwwwww' at e.i. 20 mhz to this WWWWWWWWWW at e.i. 120 khz. You see the waves get bigger?
    OK. So that is just a change in the amplitude (size, power, energy, volume) of the waveform. It doesn't change the frequency.

    sometimes they do the 'DNA' waveform. I call it DNA because it looks like a DNA strand but not.
    That sounds like a sine wave.

    Cool. Are you saying that if i attach a potentiometer to the coil or capacitor, i could change the amount of current produced to fit a desired frequency?
    You can build a tuned (resonant) circuit using a resistor and capacitor (or resistor and coil) but this will require some active components as well (to provide feedback). Then you can change the resonant frequency by changing the resistor.

    But doesn't the frequency change as you apply the number of turns on a coil, thickness of a coil and the amount of current/voltage applied?
    The number of turns is the main factor. The size of the coil will also affect it. The voltage and current won't.

    Also i was thinking if there was one frequency and the amplification part were to change the amount of waves generated at that frequency, wouldn't that mean it's possible that a wave sent could be adjusted? What i mean by this is the amount of waves sent such as ------------- (rapid waves) and this _______________ _______________ ________________ (Long waves)
    Ammplification just changes the amplitude of a signal, not the frequency.
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    Quote Originally Posted by Strange View Post
    That sounds like a sine wave.

    You can build a tuned (resonant) circuit using a resistor and capacitor (or resistor and coil) but this will require some active components as well (to provide feedback). Then you can change the resonant frequency by changing the resistor.
    Ok, so if i was looking to send out something like 13 - 60 pulses per second and 1 - 4 pulses per second, does that mean i am sending it out on a frequency between 1 - 4 hz and 13 - 60 hz or am i getting the calculations wrong? pls show me if i am getting wrong. Also i had a look at the resistor/capacitor and resistor/coil layout. I don't understand how the feedback part works and how it changes the resistor that changes the resonant frequency.
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    This shows how to build a resonant circuit using inductors, capacitors and resistors.
    RLC circuit - Wikipedia, the free encyclopedia
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  11. #10  
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    Quote Originally Posted by Sci_Research View Post
    Ok, so if i was looking to send out something like 13 - 60 pulses per second and 1 - 4 pulses per second, does that mean i am sending it out on a frequency between 1 - 4 hz and 13 - 60 hz or am i getting the calculations wrong?
    Yes, hertz (Hz) is cycles per second.

    Also i had a look at the resistor/capacitor and resistor/coil layout. I don't understand how the feedback part works and how it changes the resistor that changes the resonant frequency.
    You can build a resonant circuit from just resistors and capacitors. If you apply a signal to it, it will resonate when the frequency matches the resonant frequency of the circuit. So you can use it as a filter. But it will not oscillate by itself. To make it oscillate you need to apply a signal to it, measure the response and then feed this back as the applied signal. (It's actually rather more complex than that you have to consider phase shifts, etc).

    Once you have such an RC oscillator, you can adjust the frequency by adjusting the resistance. The advantage of that is that it is very easy to make variable resistors. Or you can use a transistor as the adjustable part of the resistance and build a voltage-controlled oscillator.
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    Quote Originally Posted by Strange View Post
    Thanks Strange. So if i get an inverter to power up the oscillator, then find out which resistors and capacitors fit into LFO's, audio and RF oscillators and add a VCO does that mean to send out a wave i just need to add an antenna?
    Also, i am serious about building this for a small project, to see if the waves come out on computer or something. Is there anyway you could guide me through building it? i don't mind how long it will take and afterwards i'll give you credit as the tutor.
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    I get the impression that you don't have anywhere near enough understanding yet to attempt to build such a thing (and I don't have time to help). Designing filters and oscillators can be tricky, especially if you get into RF frequencies.

    This is a quite a good book that covers both theory and practical examples: http://www.amazon.co.uk/Art-Electron.../dp/0521370957

    Others may have other recommendations.
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    Quote Originally Posted by Strange View Post
    I get the impression that you don't have anywhere near enough understanding yet to attempt to build such a thing (and I don't have time to help). Designing filters and oscillators can be tricky, especially if you get into RF frequencies.

    This is a quite a good book that covers both theory and practical examples: http://www.amazon.co.uk/Art-Electron.../dp/0521370957

    Others may have other recommendations.

    That's ok Strange. Thanks anyway. I'll see if i can build a simple one first and go from there.
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  16. #15  
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    [QUOTE=Sci_Research;396455]
    Quote Originally Posted by Strange View Post
    I get the impression that you don't have anywhere near enough understanding yet to attempt to build such a thing (and I don't have time to help). Designing filters and oscillators can be tricky, especially if you get into RF frequencies.
    Hey, i did some work on it. I found out that 6.5 Henries with 0.47 microf = 0.57 hz which is good start. but i wanted to know how could you have a linear pot move with 3 different selections? I mean which circuit would be best suited for this application? (LC, RLC, etc.)
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