[net.audio] video terminals VS cassette tapes

andrew@garfield.UUCP (Andrew Draskoy) (07/27/83)

From: garfield!andrew (Andrew Draskoy)
Newsgroups: net.audio
Title: video terminals VS cassette tapes
Article-I.D.: garfield.447
Posted: Wed Jul 27 01:20:53 1983

Here's a question for all you audiophile hackers:

I've been told that most video terminals give off various forms of
electro-magnetic radiation.  Do I need to fear for my cassettes when
I have them near my terminal?

				Andrew Draskoy
				{allegra, ihnp4, utcsrgv}!garfield!andrew

brian@sdcsvax.UUCP (Brian Kantor) (08/04/83)

On terminals with steel cabinets, no fear, the cabinet will contain the
magnetic fields pretty well.  It wouldn't be smart to store your
cassettes on top of it, though.

On plastic (sigh) VDTs, there are several magnetic fields inside that
might get out: the field from the deflection coils that sweeps the
electron beam around the screen; the field from the "flyback"
transformer that generates the high voltage to light up the screen; and
the field from the power transformer.

It's in the manufacturer's own best interest  to control the escape of
these fields from the components that use them, simply for efficiency
reasons (wasted energy), but some escapes anyway.  These fields do
decrease rapidly with distance, but sometimes those coils and
transformers are pretty close to the cabinet faces.

Most telephones are not very well shielded magnetically either; this is
not to suggest that they represent a danger to cassettes, but rather as
a means of testing your terminal.  Just put your phone on top of your
crt, and if you hear buzzing, whistles, high-pitched (~ 15Kc), or hum
during a conversation that goes away when you move the phone or turn off
the terminal, chances are pretty good that the cassette wouldn't like it
either.  This is a quick and dirty test, with no guarantees, but since
most everyone has the necessary test equipment (until Ma Bell get her
rate increases), it might be worth trying.  (By the way, the magnetic
fields generated by a telephone are extremely weak, which is why they
generally are not well shielded - they don't have to be!)
-- 
   Brian Kantor, UCSD.  {philabs,ucbvax} !sdcsvax!brian
		        		  sdcsvax!brian@nosc