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Ground Meter?

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Alan

Wed Oct 17 2007, 07:30PM

Registered Member #1069 Joined: Wed Oct 17 2007, 06:23PM
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Posts: 22

The basic idea for these devices is that EM waves go into the device and sound waves come out of speakers in the device or headphones. I used one once although I know nothing of where the person who showed me it is now. With it I could hear.

Wrist watches (crrrr, swish, crrrr, swish, etc..., only at very close range)
Remote controls (bleep, beepy, tweet, bleep, bleep, etc...)
Thunderstorms many miles away (odd muddled scratch low frequency tweety noise, hard to describe)
Laptops (fuzz)
a CRT TV that was on (fuzz)
Wires in walls (A low frequency buzz)

The device I presume had a coil\coils and\or an aerial\aerials or other electrically conductive components inside. It also had a dip meter on the front of the outside of the device (looked like a very short florescent light).

I presume the makeup of such a device would have to be very careful not to interfere with itself.

Alternatively some analysis could be done and information could be displayed. Such as a list of all electronic components in range and what they where, (ipod x 2, mobile phone x2, other hand-held device, TV, Radio signals, TV signals, CRT Monitors etc...). A directional version would also presumably be possible.

I also presume that frequency analysis would have to be done to shift frequency's to high or low up or down, something like a logarithmic curve between EM frequency and the frequency you could hear would be good.

Shaun

Thu Oct 18 2007, 04:44AM

Registered Member #690 Joined: Tue May 08 2007, 03:47AM
Location: New Jersey, USA
Posts: 616

That sounds like a really cool device. I would definitely build one it it wasn't too complicated (sounds like it would be tho!).

Off the top of my head I can think of things that respond to some of the stuff you mentioned, for example you can hear lightning on am radios, and this I once modded with a speaker to hear a 60Hz tone in proximity to live mains (extremely easy 20min project).

I couldn't find anything about this on google, but if you find a schematic please let me (us?) know.

Bjørn

Thu Oct 18 2007, 05:16AM

Registered Member #27 Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058

A microphone amplifier and a suitable coil would do that. Not sure about the thunderstorm, I have never tried that. Since accuracy is not important you can use the simplest of amplifier with enough gain.

It is simple to test if a coil is suitable by just connecting it to the microphone input of the PC. Remember to set the microphone boost in the recording properties if there is such a setting. You should then be able to listen to all sorts of devices and with some luck also record VLF transmitters.

Dave Marshall

Thu Oct 18 2007, 12:18PM

Registered Member #16 Joined: Thu Feb 02 2006, 02:22PM
Location: New Wilmington, PA
Posts: 554

Any device capable of detecting signals up to a few hundreds of KHz would have no problem at all detecting thunderstorms at substantial distances.

Below about 15KHz you get a phenomenon known as Spherics and Whistlers (atmospheric noise usually initiated by lightning) and up to 25MHz or so, lightning strikes out to about 500 miles are audible as intense static crashes. Perhaps when the storms in the Ohio Valley kick off this evening I'll jump on 3 and 5MHz to make a couple audio captures.

As for the other sounds, I agree with BjÃ¸rn. Any coil should do, though personally I'd focus on maximum bandwidth to allow reception of the widest spectrum possible. Similar to the coil, any HF receiver can hear most of those things (whether you want them to or not) under the right conditions.

Dave

Alan

Thu Oct 18 2007, 04:30PM

Registered Member #1069 Joined: Wed Oct 17 2007, 06:23PM
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Connected to a PC is not going to be much good, it's got to move about and also the PC is going to give off a lot of EM noise.

Tom540

Thu Oct 18 2007, 04:37PM

Banned on 3/17/2009.
Registered Member #487 Joined: Sun Jul 09 2006, 01:22AM
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I know if something that will do that. There s a wire tracing system called fox and hound.

The receiver can be brought close to wires electronics and you can hear whats going on. We had one at a place I worked and I was playing around with it. You can hear sounds on lan lines phone lines, ac outlets arcade machines computers. it was really cool. The arcade machine was making a weird beep noise every few seconds. I almost bought one to play with and to see how it worked.

ShawnLG

Thu Oct 18 2007, 05:45PM

Registered Member #286 Joined: Mon Mar 06 2006, 04:52AM
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I have built something like this years ago. It may have been posted on the old fourm. I belive that this device is called an ELF receiver. I have used a large solenoid coil with a large iron bolt through it. This is then fed through a low noize OP amp such as an OP07. then through a final amp which drive a speaker. I was able to hear the 60hz mains over one mile into the woods with a portable version. In the woods where the interference is low I can hear the natural EM sounds such as spherics and whistlers.

If you do not have a low noize OP amp you could use a J-FET or maybe a J-FET input OP amp.

I have tried to find any ELF military transmittions and the Schumann Resonance with spectran, but my location is too noizy.

This site has everything you would ever want to know about ELF radio.

Alan

Thu Oct 18 2007, 11:00PM

Registered Member #1069 Joined: Wed Oct 17 2007, 06:23PM
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It seams that both ELF and VLF span human hearing and so could be transfered directly from EM to Sound.

Id love to know if there are any hand heled sized ELF\VLF receivers on the market and more details about the fox and hound, can't seem to find much detail about it apart from that it is for testing wires.

Nik

Fri Oct 19 2007, 03:47AM

Registered Member #53 Joined: Thu Feb 09 2006, 04:31AM
Location: Ontario, Canada
Posts: 638

A hand held VLF reciever would be a really long wire, an amplifier (some op-amp) and a speaker. I had decent luck with a long wire and my laptop line-in.

Dr. Dark Current

Sat Oct 20 2007, 06:58PM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

I've just built a quick&dirty version using a coil from big relay and TDA2822M battery-powered audio amp (requies 2 external components) and it works just fine. When nothing is near the coil I can hear some tones and noises and as I move hand near it, the tones and noises change like tuning an old AM radio. Touching any wires changes the output a lot too. I've tried a remote control and mobile phone, the remote control makes interesting sounds (in some conditions these can be heard with the remote control up to 50cm away from the coil).

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