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FM transmitter power

Discussion in 'General Electronics Discussion' started by pidja105, Oct 11, 2017.

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  1. pidja105

    pidja105

    106
    1
    Oct 16, 2015
    Hello,
    Can someone here tell me approx. power of this transmitter in attachment?
     

    Attached Files:

  2. davenn

    davenn Moderator

    13,424
    1,803
    Sep 5, 2009
    with a BC548 ( a very poor output choice) probably less that 100 mW ( at first glance, I was initially thinking maybe ~ 10 - 20 mW)
     
  3. pidja105

    pidja105

    106
    1
    Oct 16, 2015
    If I replace transistors with bigger power ones, do I need to replace something more, or power will be increased only by transistors?
     
    Yan Kyaw Min likes this.
  4. duke37

    duke37

    5,273
    733
    Jan 9, 2011
    You will need to do a redesign, changing resistors, capacitors and inductors. Also you may need more gain by adding another amplifier. It will all depend on the frequency which is not specified.
     
    davenn likes this.
  5. Audioguru

    Audioguru

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    Sep 24, 2016
    It is obviously designed to operate on the FM broadcast band around 100MHz. It will sound muffled because it is missing pre-emphasis that ALL FM radio stations have. All FM radios have matching de-emphasis.
     
    hevans1944 likes this.
  6. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    May 8, 2012
    There's a huge chasm between the name of that .gif and the circuit design. A far more appropriate name would be "Basic FM Transmitter.gif".

    Chris
     
  7. Audioguru

    Audioguru

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    Sep 24, 2016
    It is not a basic FM transmitter because it has an RF amplifier so that the radio frequency does not change when something moves towards or away from the antenna which happens if there is only the RF oscillator transistor (and the antenna connects to its tuning LC).

    But its radio frequency will change anyway as its battery voltage runs down because it is missing a voltage regulator.
     
  8. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    May 8, 2012
    An ignition coil, sometimes called a spark coil is intended to provide the spark required to ignite the compressed air/fuel mixture within the cylinder of an internal combustion engine. It also makes one hell of a wide band transmitter! Does the name Marconi ring a bell?

    Besides that bit of minutia here's my take on that circuit:
    T1 serves the function of OSC/Modulator. Intended to pull the center frequency (fc) in proportion to audio input level. It's intent is to produce FM. I'm sure it will but it will also produce a fair level of unwanted AM. In short it's only fit to demonstrate the FM concept.

    T2 is the RF Final lacking any (but preferable) buffers / drivers. While the choice of BC548 is poor it doesn't change its function. The fact that moving near the antenna will reflect back to the oscillator (pulling it) is also true but it still doesn't change the fact that T1's function is as an amplifier.

    I won't criticize the value of that circuit. It serves its purpose of demonstrating the basic FM concept. This is where students start .... the "Basics". ;)

    Chris
     
    Last edited: Oct 12, 2017
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