Science Buddies: "Ask an Expert"

Okay. I am going to do the idea with the dimmer lights to make electromagnetic interference and test the disturbance on a handheld radio. I understand the concept of it now. I am also going to test different shields on the radio to find if I can block the disturbance.

The big questions I have now are:
I need to find the frequency and power of the interference made by the dimmer switch!!?
Also, I need a way to make my data numerical. As far as I know, I am just testing to see if there is interference or not. Can i test it with a decibel reader or something? Won't the interference from the dimmer light mess up the decibel reader? I really need help.

I'm sorry if this doesn't make sense. Its pretty hard to explain. See my other forum topic to get more sense out of it.

Well, to start off with, you'll want to get your nomeclature correct. The kind of noise you'll get off of a dimmer switch is not EMP, but EMI (electromagnetic interference).

EMP is usually defined as a very large amplitude, short, broad spectrum EM field, generally created by lighting, nuclear weapons, and a few other outlandish things like that.

Anyway, there are a number of ways to measure EMI, but most of them require moderately expensive equipment. Your idea of a DB meter measuring the noise coming out of the radio is a reasonable one. I can't think of a better idea off the top of my head unless you have access to a digital oscilloscope.

If the dimmer switch were putting out an actual EMP, it's reasonably likely that the DB meter would be affected too. However, with this kind of low level interference, the DB meter is unlikely to see it. They have filters, and even the inertia of the needle would likely damp out any noise at these kinds of frequencies.

The biggest problem you're going to have is controlability and repeatability. There are a lot of sources of electrical noise out there in the world, and they vary rapidly.

The way actual radio engineers do this kind of stuff is to work in an anechoic chamber (look that up for your research). It's a faraday cage (look that up too , that also is designed not to reflect EM waves, so measurements are more controllable.

You could, I suppose, come up with some way to build your own faraday cage out of metallic screening material so you can keep out the outside noise.

On the other hand, if you did a lot of background measurements without the dimmer on, you might find that your location doesn't have much EM noise, and you could account for the background noise levels in your measurements.