A simple directional microphone with a reflector for listening to weak audio signals from a distance. The audio amplifier is built around three transistors, the gain of which is adjusted by resistor R3. The 2SC3199GR transistor was chosen for its low noise level. Another low-noise transistor can be used instead.
Powered by a 3.7V battery. The amplifier is powered by a low-ripple power source. If the amplifier is powered by a source with ripple, you will hear it in your headphones. This is why it's best to power the amplifier from a battery.
I cut the reflector out of a 25-liter plastic bottle. You can take a different reflector and of different sizes.The cable from the microphone to the amplifier input needed to be shielded, so I used a USB cable.
The microphone must be placed at such a distance from the reflector that the reflected sound signals from the reflector will be maximally received by the microphone.
Connect the microphone to an oscilloscope to monitor the signal level. Place a sound source, say a 1000 Hz signal from a generator, near the reflector. Glue a curved plate to the microphone. Use the microphone to find the maximum signal reflected from the reflector and secure the microphone.
This is where the signal level is at its maximum, so I leave the microphone in this place.
It's time to test the directional microphone. I went out into the forest where there are birds perched in the trees. By pointing the reflector at a weak sound source, I can hear an amplified signal in the headphones.
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