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“as i understand it, the basic idea is that you use your audio source to modulate the amplifier’s power supply via either a transistor or a transformer. there seems to be lots of ways to do this but i am having trouble finding detailed explanations.”
Carl, one of our contributors, started and maintained a thread where he detailed his development of a 13.56 MHz transmitter. You might find some good information here: http://part15.us/node/2870
I advise using high level modulation instead of low level modulation for an AM only transmitter. Low level modulation requires a linear final amplifier and its attendant lower efficiency compared to class C, D, or E. It is easy to produce the required audio power for 100 mW AM transmitters. An IC such as the LM386 audio power amplifier can readily drive a modulation transformer at these power levels. This chip looks like it could be used to supply both the modulation and power to the final since it is DC coupled and has self centering output which could be changed using the + or – input or by using an adjustable LM317 regulator for the LM386 supply. A transformer wouldn’t be needed if this is the case. As a starting point, a class C, D, or E final designed for a 50 ohm load would require about 2.5 to 3 volts at 40 mA from whatever power supply is used for 100 mW operation.
I have seen nice tutorials on AM schemes and if I run across them I will post. Otherwise, a net search may turn up what you seek.