An Advanced Barking-Dog Silencer. Or Is It ?

In 1998, I was instructor for two 3Hr (6Hr days) circuit development and proto-typing classes of 28 men & women, and we had class four days a week in electronics & computer technology.

One of the goofy gadgets I assigned for my classes, was to tune their home bedroom-radio to whatever broadcast station their noisy neighbor’s alarm radio was tuned to, plus the internal “Beat-Frequency” of their own.

The result is an unbearable feed-back screech on the offender alarm-radio, causing it to blare out a most uncomfortable noise.

I didn’t have a purpose for the stunt, I only wanted my students to learn the topic.

Another project, was a Barking-Dog silencer.  With a microphone & speaker, my class built a circuit which would capture the barking-input with the microphone, simultaneously invert that audio input & amplify it, and send that output to the speaker.

The result is that you can see the dog wagging his mouth, but you can’t hear the bark.

That circuit has been known to electronics nerds for a long time.  In fact, this technique is used in aircraft, like helicopters, to damp out the sounds outside the chopper so the pilots can hear each other.  You can also find headphones for the shooting-range to dampen the amplitude of your firearm.

I’m pretty sure the “inverter” circuit is used all over the place.  I’m rather amused to see the Japanese have created another useless invention and am not surprised they believe they can use it as a weapon.  I wonder if they know it only works for the ears of the user?  The two people standing beside each other, won’t be aware someone is trying to use it on them.

On the dark side of that device, looking only at the diagram, the way the device depicted in the article operates, it can eavesdrop on office windows at a very respectable distance.  When you point that Lazar at a window-glass one or one thousand feet away, the reflected light from the glass, varied by the air pressure inside the room, vibrating because of a conversation taking place in, what had been presumed to be a private conversation, can be captured and recorded, somewhat like the Barking-Dog I mentioned earlier.  That is exactly the reason there are no windows in the CIA building in Langley.

Electronics is fun to play with, ain’t it?