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Amplifying an AM signal. Very cheap equipment.

Discussion in 'Radio and Communications' started by Acid Wire, Aug 24, 2010.

  1. Acid Wire

    Acid Wire New Member

    Joined:
    Aug 24, 2010
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    Hi there!

    I'm new and I tried to look around in existing threads... but I couldn't exactly find what I need. I've built a simple AM radio transmitter with cheap equipment. It's for a science project.

    [​IMG]

    I amplify the signal that goes into my Ipod's headphones, and I add an Offset to it with a simple pair of TL072CN Op-amps (the amplification does not appear on this diagram). Then, with just an AD633JN multiplier and an astable multivibrator (another TL072CN, see diagram below), I do the Amplitude Modulation and have a signal of about 0.80 MHz.
    For all this equiment to work, I have also built my own symetrical -15V/+15V alimentation using transformers, regulators, capacitors and diode bridges. So far, it's cost me very little money, I will not give the details of how I built this symetrical alimentation, since it's not what I'm worried about.

    [​IMG]

    Now, I would like to broadcast this signal. I have 100 meters of cable that I intend to use as my antenna. I need to amplify it beforehand. The problem is: I can't really use an Op-amp to do the job. I'm guessing if I want to broadcast my signal over a 3 mile radius, I need better than an Op-amp...

    ... So: I'm considering the possibility of using a Push-pull amplifier using transistors, but I have a problem: this is beyond my knowledge! I know how to use Op-amps, multipliers and other simple kind of equipments, but I have no idea how transistors and Push-pull amplifiers work. I'm only considering this option since it's advice I've received from a store keeper, but I have no idea how qualified this store keeper really is.

    My question is: Is it a good idea to use a Push-pull amplifier to amplify my 0.80 MHz signal in order to broadcast it over a long distance? What is the bandwidth of such a system? If a Push-pull is a bad idea, how should I amplify my signal before plugging it into the antenna?

    Thanks a lot!
     

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