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Transformers

Discussion in 'General Electronics Discussion' started by Bluepoint SEO, Jul 28, 2016.

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  1. Bluepoint SEO

    Bluepoint SEO

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    Jul 28, 2016
    Of course I'd still be checking the laws before hand.
     
  2. Chemelec

    Chemelec

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    Jul 12, 2016
    This Circuit is from an OLD, "Popular Electronics" Magazine.

    L1 is a Standard, Adjustable AM Oscillator Coil.
    For Really SHORT DISTANCE Transmission, Do Not add the Antenna.
    AM-Transmitter.PNG
     
    Last edited: Jul 29, 2016
  3. Bluepoint SEO

    Bluepoint SEO

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    Thanks for this Gary and it was nice to speak to you.
     
  4. davenn

    davenn Moderator

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    OK here is a basic FM transmitter ... commonly known as a "bug" transmitter

    [​IMG]

    its about as basic as you can get and you use a standard FM band receiver to receive the signal

    Many electronics shops sell kits for these projects



    Dave
     
  5. Chemelec

    Chemelec

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    Jul 12, 2016
    Dave, He wants AM.
     
  6. duke37

    duke37

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    Bore da.
    There are persons out in the wild world who repair old valve radios and want to use them with various signal sources. The diddy transmitters have been called pantry transmitters. Various ones are out there, either built, in kit or circuit only. Some are quite complex and give low distortion and high modulation index.

    I would think that you could do better than the very old circuit as shown by chemelec (#22), use npn transistors and better biasing.
     
    davenn likes this.
  7. davenn

    davenn Moderator

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    Last edited: Jul 30, 2016
  8. Bluepoint SEO

    Bluepoint SEO

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    Hi yes the question was originally started as a transformers question but veered into AM. Either way I'm happy I've taken 3 things away from this thread so far 1) transformers do not convert DC to AC, 2) FM transmitters can have fairly simple design and 3) FM transmitters don't need a crystal oscillator. Good stuff thanks everyone for the input and diagrams. Actually I've taken more than those 3 away like mics already create AC. Thanks again!
     
  9. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    Looking at all three circuits posted I find an irony embedded in them. The first one is the oldest design, which uses germanium PNP's. Yet that old design will probably fit a basic communications precept better than the other two. I'm referring to an AM transmitter will (ideally) not pull the Osc. freq when speaking into the mic and thus 'not' also transmit an FM component. Conversely an FM transmitter will not (ideally) transmit an AM component.

    Admittedly this observation is a trivial issue in this application but I thought it was worth commenting on. BTW that first PNP circuit employs a modulator that would be pseudo synonymous with preferred Plate Modulation vs Grid Modulation.

    Chris
     
  10. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    Since this was your original question the answer is no. Here's what the outputs of a 1/2 wave rectifier vs. a Full Wave Bridge look like prior to filtering it with a capacitor.

    The transformers in both circuits are 4:1 Step-Up Transformers. Thus they output a voltage 4 times the input voltage supplied by VG1, which swings to +10V Peak and -10V Peak = 20VPP.

    Chris
    upload_2016-7-31_12-6-27.png
     
    Last edited: Jul 31, 2016
    Arouse1973 likes this.
  11. Bluepoint SEO

    Bluepoint SEO

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    That's interesting; if you turned the transformer around i.e. 1:4 I'm guessing that would work as a 1/4 of the input voltage but 4 x the current? I could Google all of this but I'd much rather speak to real people. :)
     
  12. Chemelec

    Chemelec

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    Yes, as long as the input voltage is suitable for that particular winding.
    If you Exceed the proper input voltage for the winding, the transformer will overheat and eventually be damaged.
     
  13. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    While two or more transformers may have the same input/output voltage rating, or better stated "Turns Ratio", they can have totally different current ratings. Basically the larger the wire gauge the higher the current rating. This in turn dictates a larger transformer core.

    You're understanding of the relationship of primary voltage/current vs secondary voltage/current is correct. Current drawn in the secondary is reflected back to the primary and divided or multiplied by the turns ratio. ;)
    Chris
     
  14. Bluepoint SEO

    Bluepoint SEO

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    Jul 28, 2016
    Wahhh so much to learn haha. Brilliant. Thank you guys.
     
  15. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    Well, it's quite fortunate for you that somehow you found your way to EP. Where elitists snobs are not celebrated. ;)

    Chris
     
    davenn likes this.
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