Somewhere in the early 60s, one device was patented in the USA, which is a radio transmitter that does not require the usual power source.And it feeds on the energy of sound.In fact, it is an eternal and “spy” transmitter.The louder the sound, the more powerful the radio transmitter will emit.The sound receiver is a speaker that converts sound into electrical vibrations.Well, then these oscillations are rectified into a constant voltage that feeds the simplest transmitter.I decided to check if this is even possible.
What will be required.You need a speaker with a possibly large diffuser and a resistance of 8 ohms or more.A 220 Volt mains step-down transformer, I took the first one I came across without selection.Any germanium diode is suitable for a rectifier, there will be a slight voltage drop on it.The germanium transistor chose П27A, it works perfectly when powered from 110 millivolts and up to 1 MHz frequencies.
The inductor coil contains 20 turns of 0.14 mm wire wound on a ferrite core with a diameter of 8mm and a length of 2 cm.This is an experimental coil and you can wind it on another ferrite.
Now check.First, we look at the sound voltage that will be on the terminals of the transformer 2.It has a large amplitude, the transformer has increased the sound voltage from the speaker to the voltage we need.We look at the signal from the output of the transmitter.As you can see, this is a high-frequency signal with frequencies up to hundreds of kHz.
Now it remains to place the receiver next to the transmitter coil and catch the signal from the transmitter.It is necessary to speak loudly into the speaker with your palm covered.In the receiver you will catch the harmonics of the transmitter at frequencies 700-1500 kHz, tune in to the best signal.
