Capturing EM interference with a microphone

jh wrote in news:no-96791C.01580504112005@localhost:

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Any way you can wrap the mic in a "sound proofing" material, so you damp out the acoustic pickup and leave the EMI sounds?

the reason for that is that the dynamic microphone has a voice coil (like in a loudspeaker) anf that coil picks up all the electromagneic interferance (EMI) inside your computer.

You'll need to shield it against EMI. while not blocking too much sound that that won't be easy. basically you need to surround it with a conductive shell, electret mikes (like the "ctrappy lapel mike") are constructed that way.

Bye. Jasen

Try something like this...

|--------------- ----------------+---///////-------+--------| | | |-------------- K r | A | | | | | +-----------------+--------+

where the antenna on the left is maybe 6-12" of wire, K-A is a small schottky diode, 1N5711 maybe, R is 100k, output is audio coax.

Oh, ////// is a small inductor, 100 uH or something. This should pick up both baseband signals and detect RF. Drive a high-impedance audio input.

John

Hi Josh: The high frequency noise is from the cmos technology switching between 1 and

10 nanoseconds or 100MHz to 1 GHz. This noise passes thru the microphone cable and into the amplifier circuitry. At these high frequencies, the signal is rectified and what you hear is the peak detection of the noise. The only other noise is the switching power supply that creates a 1 MHz pulse every 20 to 40 useconds. Therefore, the best way to hear electronic noise with the existing amplifier is to just use a piece of wire about 2" long that connects the shied or ground wire to the signal wire. You don't even need the microphone. This is basically a UHF antenna. Enjoy Harold

An easy way, use an in-ear earphone, or other earphone. They've got a coil of wire inside to pick up EMI, and a jack plug on the end. Tho they're comparitively lo-impedance but, it's an experiment innit?

Like others have said, put a bit of plasticine over the sound holes.

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if love is a drug, then, ideally, it's a healing, healthful drug... it's kind of like prozac is supposed to work (without the sexual side effects and long-term damage to the brain and psyche)

Using an earphone to capture EMI looks usefull to me, but I'm not sure I understood the principle. Please, what to do exactly with an earphone? Should I connect it to aditional power source (like batery) to drive the earphone, or no need? Should I, on the plug side of a cable, make something like antenna?

Nikola

On Tue, 8 Nov 2005 08:22:37 +0100, "Nikola Bosnjak" sprachen:

Just connect it to the mic socket on your tape recorder (or an amplifier or whatever), instead of a microphone.

It's a bit lo-impedance to be ideal, but should work.

No! Just plug an earphone into the mic socket. That's it!

Altho, as an experiment, you could try the antenna. Just a piece of wire, connected to one of the contacts on the jack plug.

I'd like to hear about your results.

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if love is a drug, then, ideally, it's a healing, healthful drug... it's kind of like prozac is supposed to work (without the sexual side effects and long-term damage to the brain and psyche)

Ok, you'll know when I get result.

Basicly, the point is to examine EMI in navigation devices on ships, becouse it can be the reason for some malfunctioning, sometimes. Using osciloscope or other measuring devices is hard (hard to cary it all the time when going to service). Once I saw a man wearing in-ear phones, probably driven with batery, and touching the electronic circuits with conductor (from earphones). He was using earphones instead of an osciloscope. So, what to do to use same principle to measure EMI?

Nikola from Croatia

I thought I posted something, but here goes again.

A telephone pickup coil is an inductive pickup. I think they still sell these.

I listen to noise via a portable handheld amplifier, just an op-amp. I have a switch to either connect a coil or just a rod antenna. The gain is adjustable. Noises from magnetic vs electrostatic can sound very different. Magnetic also penetrate metal. Static magnetic fields can be heard when positioning the coil, but a Hall Effect sensor would be best at this. I still need to configure to measure other noises. I need to connect a photodiode to listen to light noise, 60 Hz etc. DC light should be free of noise. I also need to measure vibration. A vibration sensor will connect to bottom of handheld device, so when its sitting on a table, the noise can be heard. I also need to measure LF audio, as in ventillation noise and changes of less than 10 HZ. This is not just a usefull device I carry, its necessary!

Therte is a product which is basically my electrostatic sensor It says inductive pickup, but I think its really just a rod.

greg

Here's a good link.

Also try and put a radio real close to your computer and see if it slows down any processes. Start at 100Mhz transmitters and work up.

I guess the experiment would be like a counter for 10 second... see if it counts the same number after 10 seconds has elapsed. Then try to scale the distances.

Marc