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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

    Aug 24, 2010
    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.


    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.


    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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