http://www.ebay.com/itm/50mW-AM-Transmitter-DIY-Kit-for-learning-/152523...
I found this small AM broadcaster kit on eBay and built it, take a look at the schematic, at first it looked like the modulator control just varied the audio input and this was amplified by the two transistors controlling the DC voltage to the RF power amplifier in order to modulate .
However under test I found the RF amplifier when not under any modulation and the control turned all the way to minimum modulation, the RF amplifier will put out about 300 Mw. When modulating the transmitter so you get 100% modulation, the power output drops to about 50 Mw carrier as advertised.
The power from the amplifier does not increase under modulation when read as a DC voltage though a diode across a 50 ohm dummy load.
Can anyone explain the modulator circuit to me?
Thanks,
Radio Joe