Tuesday, 15 February 2011

Low Cost Powerful AM Transmitter (13Km)

This is a simple AM Transmitter Circuit, but Its very powerful one. It can transmit SW range signals within 13Km circular area. Use external antenna for best results. I recommend to use 12V battery as the power supply. If you hope to using 12V AC-DC adapter you may want to keep very smooth DC out put using stabilizer, unless it will generate low frequency hum when listening to radio out put.  Better to read following instructions before assembling the circuit.


> L1 Coil

Use 22SWG copper wire and make 10 turns, Insert a ferrite rod in to the coil. see figure 1.

>> L2 Coil
Use 22SWG Copper wire and make 10 turns. Don't use a ferrite rod. Coil diameter is 0.6 cm ( 1/4' ).
>> X-tal (Crystal)
Use 4.4333MHz crystal.


  1. * The audio qaulity of this simple circuit is likely to be very mediocre!

    * Carbon mikes are hard to find these days...

    * 4.333 MHz is NOT a licenced frequency, & with the power mentioned all manner of woes may result.

    1. Yo, Anonymous. Which country's laws are you an expert of? You can always change the crystal. If you are a licensed HAM I'm sure a crystal of 3.885 or 3.887 mhz will work just fine and it will be a US "licenced" HAM AM frequency. I currently have a 4.000 mhz crystal in the one I built and it looks very cool. I did not have to change the capacitance of components at all. The audio quality is very good. I'm using a mic element from an old phone. (lots of those at the thrift store; that's where I got mine). I'm not even finished yet. I'm adding an amplifier. This thing rocks! You are a real downer.

    2. Can I use this on Philippine radios with frequency range of only KHz?

  2. I have actually built this circuit and it performs well. With the wide range of antenna matching provided by the pi network it will be great to put a 4.000 MHz crystal in it when they arrive and then to add another air variable to bend the crystal down a bit into the 80 meter ham band. Then I will build a simple linear. I'll mount the whole thing and a nice meter in a metal filing cabinet and it is going to look boss as hell. Nothing is hard to find these days. You just have to know where to look.