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From: truesdel@sun418.nas.nasa.gov (David A. Truesdell)
Newsgroups: comp.sys.ibm.pc
Subject: Re: GAS PLASMA SCREENS!!
Message-ID: <5601@amelia.nas.nasa.gov>
Date: 12 Apr 90 20:10:52 GMT
References: <1990Apr10.002440.9812@ux1.cso.uiuc.edu> <1074@lectroid.sw.stratus.com> <5096@cbnewsl.ATT.COM>
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feg@moss.ATT.COM (Forrest Gehrke,2C-119,7239,ATTBL) writes:

>In article <1074@lectroid.sw.stratus.com>, dts@pwllheli.sw.stratus.com (Daniel Senie) writes:
>> In article <26226d66.1467@petunia.CalPoly.EDU>,
>> jdudeck@polyslo.CalPoly.EDU (John R. Dudeck) writes:
>> |>CRT's DO NOT emit any radiation other than visible light!
>> Explain this: Take the handset off of a standard telephone (Bell 2500
>> saeries, for example) and unplug it from the phone. Hold the handset
>> near your CRT and put your ear to the receiver. Where do you suppose the
>> buzzing noise you hear is coming from?

>Before we get too far down this path, let's be certain everyone
>knows the difference between electromagnetic radiation (radio,
>for instance), and ionizing radiation (xrays, for instance).

Yes, lets make sure that everyone DOES know the difference between
between radio waves, and x-rays.  Except for the energy level of the
photons...

	THERE IS NO DIFFERENCE.

Radio waves and X-rays are just differnt forms of the same thing.

If you don't understand this I'd suggest that you refresh your knowledge of
basic science, and quickly.

>What you are hearing in your telephone is the detection of the
>scanning circuits electromagnetic radiation.  If you place a
>radio receiver near your PC you will hear all sorts of radio
>radiation produced by the various circuits in the PC.  None
>of this is produced by the CRT.  This radio emission is the
>same you will hear if you place a receiver near a TV set.

What do the "scanning ciruits" of a CRT emit?  Electromagnetic radiation.
What does a PC emit? Electomagnetic radiation.
What does a TV emit? Electomagnetic radiation.
What does a Xray machine emit? Electomagnetic radiation.

It's all the same thing, just different at different frequencys.

Oh, and a radio receiver is not the best tool for the job of measuring EM
emissions.  It's designed to only look at a small portion of the broadcast
band, which is why it can pick out individual stations.

I expect what you are picking up from the CRT's and TV sets is the fairly
strong, low frequency (10's to 100's of kHz), emissions from the scanning
circuits being picked up by the amplifier, while the tuner is probably picking
up the higher frequency harmonics from the switching of the digital circuits
inside the PC.

--

T.T.F.N.,
dave truesdell (truesdel@prandtl.nas.nasa.gov)