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radio frequency circuit design

Discussion in 'Electronic Projects Design/Ideas/Reviews' started by bananasiong, Mar 8, 2006.

  1. Roff

    Roff Well-Known Member

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    Post detailed schematics of the transmitter and receiver that you are using, with component values.
     
  2. bananasiong

    bananasiong New Member

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    yes.. the 555 is the tx and the LM393 is the rx.

    the 684R is a 1K VR.

    the LED's are connected to see whether it receives signal or not by blinking.
     

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  3. Roff

    Roff Well-Known Member

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    What are you using as a transmitting antenna? Forgive me if you've already answered that question.
    You can't make a decent receiving antenna with a 2200uF cap and a 10mH inductor. The Q of the inductor is much too low. Seeing a blinking light should not be your primary goal here. :roll:
    You would be much better off trying 10kHz, like Russ suggested. If you want to make sure your 555 is oscillating, touch a 10uF cap across the .01uF timing cap momentarily, and see if the LED flashes.
    BTW, if you have an LED in series with your loop antenna, that will reduce the current in the loop, which will reduce the sensitivity (which you may or may not need). You could use a separate LED and resistor, to either GND or +5V. you don't need much LED current. A 300 ohm resistor should suffice.
     
  4. dave

    Dave New Member

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  5. bananasiong

    bananasiong New Member

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    the 100 ohm as transmitting antenna.
    okay.. i will try to construct using the same value given by Russlk

    i don't get this, how to touch a 10uF cap across the 0.01uF? in series or in parallel and the other pin connected to the ground?


    and.. for the receiving part, i get a 1 when there is no signal, it shouldn't be, right? i connected a LED from output of the rx and ground. but it gave 1 when there is no signal. how come?? :roll:
     
  6. mstechca

    mstechca New Member

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    Why do you care?
    There is one mistake.

    According to the Receiver circuit the "tank" circuit you made is connected to the input of the amplifier. This gives the indication that you are trying to receive your signal through radio waves.

    But when I look at your so-called transmitter, it actually isn't a transmitter which works for your circuit, because it sends output to either an LED or an infrared light.

    Did you look on the internet for FM transmitter schematics?

    And, I have to agree that your inductor value is very high.

    For better performance, you should try lower inductor values. If you must keep the same frequency, just increase the capacitor value.
     
  7. bananasiong

    bananasiong New Member

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    but most of them from this forum told me that a 555 timer can transmit. :roll: :roll:
     
  8. audioguru

    audioguru Well-Known Member Most Helpful Member

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    This is how it works:
     

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  9. Roff

    Roff Well-Known Member

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    Mstechca doesn't appear to understand that a magnetic field is created by passing a current through a wire, and that, if it is fluctuating, will induce a voltage/current in a nearby wire (or coil of wire). It works the same way a transformer works.
    Mstechca, will you ever figure out that you are currently a rank novice? You need to be in the questioning and "listening" mode, and not in the answering mode, except maybe on rare occasions. When you post garbage, which is about 80-90% of the time, you just further confuse an already befuddled fellow novice. I think you are drunk on the little knowledge you have gained, and feel you must do a "core dump" every time you see a high-tech term you recognize. I don't want to discourage you from experimenting, and asking questions, but please back off a little. Some of us spend about a third of our time here doing damage control.
     
  10. hyedenny

    hyedenny Guest

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    I, too, am a novice in the first degree, but I recognize mstechca's posts as rubbish. Reading them is like reading Ken Kesey or Timothy Leary. I love the way he throws the jargon around without having the slightest idea of what hes saying! ITS GREAT!!! Some people pay to be entertained like this. Why doesnt he get a clue when people ask him to shut up?! I read the posts here as a resource in addition to my books and tinkering. If theres one thing Ive learned very quickly, its to SKIP HIS POSTS!
     
  11. bananasiong

    bananasiong New Member

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    can u tell me how to touch the 10uF cap across the 0.01uF ?? in series or parallel?

    and my output of the receiving part is always high. it should be low if there is no signal, right? but how come?
     
  12. AllVol

    AllVol New Member

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    Being also a newbie, I risk the ire of the group by pointing out that banana is trying to use a 22uF timer cap in his 555 circuit. His cycle is such a fraction of a hertz it should not be considered applicable to his project.
     
  13. audioguru

    audioguru Well-Known Member Most Helpful Member

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    "Across" is in parallel.

    Look again at my explanation:
     

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  14. bananasiong

    bananasiong New Member

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    i put the 22uF to reduce the tx frequency to around 34Hz. can it works? then what is your suggestion?
     
  15. bananasiong

    bananasiong New Member

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    okay.. thanks!! u mean, if there is no signal, the output of rx is high, and if there is signal, the output of the rx is pulses. am i right?
     
  16. AllVol

    AllVol New Member

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    what is your suggestion?

    If I were attempting this project, I would go back and do exactly what they suggested five pages ago.... and get the values right. I even question your 34 hz figure.... it's more like .34 hertz - a mere tick. And take that LED out of the output circuit of the 555. That tells you nothing.

    If you want to see if your 555 is oscillating, simply put an AM radio next to your project... tune to a blank space on th AM dial... and you can hear the 555 working. THE FREQUENCY ON THE DIAL IS NOT THE TIMER'S frequency, however, but merely a harmonic.

    As one newbie to another.... when working on a project, follow the instructions to the letter for good results.
     
  17. Roff

    Roff Well-Known Member

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    Re: what is your suggestion?

    I can't disagree with you first suggestion, but regarding the 34Hz:
    You mentioned the 22uF cap. Did you even look at the resistor values? Do the math, dude. The equation is right there in the 555 datasheet.
     
  18. AllVol

    AllVol New Member

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    Sorry if I am in error. Decimal points have always given me trouble and my calculator o'loaded! But I have fooled with 555's a lot, and know that a total of less that 1200 in both Ra and Rb, plus 22 uF gives a slow beat. If I'm wrong, another lesson learned.
     
  19. akg

    akg New Member

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    'bananasiong' , it has been already explained in the forum that the system is not entierly RF , actualy it uses magnetic induction(weak) between the loop (ant) and the i/p of op-amp. since basic principle is magnetic induction ,higher the freq better the result(refer:-rate of change of magnetic field) , The tuned ckt is used to reject other interferece emf that occur like the mains power supply freq..etc.also there is no need to use the LED .
     
  20. akg

    akg New Member

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    In the diagram u posted , the pin 7 of 393 is connected to pin 2 , that is wrong and should not be done.
     
  21. bananasiong

    bananasiong New Member

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    u mentioned this last time, didn't u? or maybe i have misunderstood with my lousy english? please forgive me with the misunderstanding.
     

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