Need help identifying a device

[alan2here]

The threat title sucks but I couldn't really fit much explonation into that space.

 

I once used a device that was a small handheld box with a speaker and a volume controll on the front it. The sound waves that came out of the speaker when it was turned on was the same the electromagnetic waves travevling though the device.

 

The end result was that just by listening you could hear distant thunderstorms you couldn't hear with your ears as they where to far away, somone who had a watch with a magnetic pendulum inside it could be heard from about a half meter away, fuzz generated by TV sets which where meters away (and there where flat screen), sets of bleeps make by pressing buttons on TV remotes and much more other stuff I couldn't Identify.

 

I am no longer in contact with the people who make them, they where paronormal invesigators and called the device a "ground meater". This was no obvious fake, they where quite genuine people and nobody was following me around pressing sound effect buttons or anything, it didn't seem possible that it was not real.

 

It is supposed to work like a radio without a tuner, I take this to mean an arial attached to an amplifier and then a speaker, however there is the problem with this that doing that you could only hear sound at cirtain frequencies and would not be able to here the watch (1 time a second) or the inferred tv remote (300,000,000,000 to 300,000,000,000,000 times a second). I know you canshift frequencies on a computer but even with my fairly high powered PC this is only moderatly good and they cannot be shifted to millions of times diffren't than there starting frequancys and still sound ok.

 

Instead of using an aerial it used what looked like a white tube that fluorescent lights use.

 

The most facinating thing about it is the diffrence in what the diffrence in sound between all thease things seemed so great that with a bit of time you might be able to tell what something was from a distance (though things you couldn't see though) by listening to the sound.

 

If it had been half the size and half the price I definatly would have bought it off him.

 

My question is can anyone fill in the gaps as to how to make it or has anyone ever seen anything like this before?

[John Cuthber]

My best guess is that it was a coil of wire, perhaps with a ferrite core, connected to an amplifier.

Any change in the magnetic field would produce a voltage in the coil and if this were amplified and fed to a speaker you could hear it. As you say, there's no way you could hear the IR remote control signal directly, but the IR signal is pulsed in order to carry information to the TV or whatever. Those pulses happen a few times a second so you could hear that.

Also, while the IR would have no direct effect on a coil of wire, the current in the remote control would vary as the IR LEDS went on and off. This would produce a variable magnetic field.

I bet you are glad you didn't buy it now.

[alan2here]

Well, It picked up a lot of stuff both emediatly obvious (as to what it is) and otherwise, I would have wanted it for just the stuff in the demonstration even if that was all it could do. You'r explanation does make it seem rather less impressive than what I had imagined. Why would IR have no direct effect on a coil of wire (as it is an electromagnetic wave)? The tube thing was attached to the outside of the device, I guess the coil may be inside that?

[Rocket Man]

IR can't produce any immediately useful magnetic effects.

it's part of the electromagnetic spectrum but the oscillations in the coil would be so fast that NO electronics could ever hope to keep up. (IIRC visible is in the terahertz range while pentium has clocked a supercooled transistor at only 500GHz)

 

that device really only picks up on electromagnetic radiation in the acoustic range (20 - 20000Hz)

[YT2095]

it`s a simple EM amplifier, and the "thing" that looks like the starter for a fluorescent tube is the coil head from a Dip Meter.

I`ve made dozens of them, all you need is a simple off the shelf audio amp and a pick-up coil, even better if you use a FET as a front end pre-amp.

VLF radio works on a similar principal, although it has Pi filters to block out 50/60Hz mains hum etc...

the noise you get from the TV is from the 16KHz flyback transformer mostly, Compact Fluorescent bulbs are as noisy as hell too!

also you`re not picking up the IR, you`re listening to the current that fires up the LED being switched on/off.

[alan2here]

Thank you all for the info

 

Email me YT2095 --> alan2here@gmail.com

 

I would be verry intrested in this. I could probbebly cover the costs of components + prophet if you could make me a good one.

[Rocket Man]

get an AM radio, as cheap as you can buy with a rotary dial. (expensive ones have all sorts of filters etc)

extend the antenna and coil it up.

tune it to a silent spot and there is a close equivalent to the device you're describing

 

i tried it with my radio, works fine as long as the source is close to the base of the antenna.

[alan2here]

One way of getting a bigger range of frequencies could be to take sample's a quickly as possible, pass them into a chip that could do spectrum analysis. Then convert the bands into addable sound at a condensed rage of frequency's?

 

Edit:

that device really only picks up on electromagnetic radiation in the acoustic range (20 - 20000Hz)

Oh

 

 

get an AM radio, as cheap as you can buy with a rotary dial. (expensive ones have all sorts of filters etc)

extend the antenna and coil it up.

tune it to a silent spot and there is a close equivalent to the device you're describing

 

i tried it with my radio, works fine as long as the source is close to the base of the antenna.

I tried doing some of this with my radio. It worked to a point.

[Rocket Man]

the am radio has a filter on it so you only get the recurring pops and crackles.

if you can bypass the filter you'll get the actual wave shapes over the speaker.

a suitably hacked radio can give you that.