burns@iuvax.UUCP (01/14/85)
The following query was posted Dec 18 to net.video, but, receiving
no responses from this lively net, I suspect that it may have dropped
into a black hole. Ergo, I am reposting it. In hopes of generating
a reply this time, I am also sending this out on net.analog.
Surely this question is not too tough for you EE types out there? :-)
I am having a cabinet built to hold a 25" TV, VCR's, assorted video
equipment and tapes. I have recently been warned that storing video
tapes within a foot of the monitor is unwise as it may slowly erase
the tapes. Since the current design has only about 5" separation
from the bottom of the monitor to the top of the tapes, I'm concerned.
It would be difficult (expensive) to modify the design at this point.
Question: is there an effective technique for shielding the tapes from
the offending magnetic source?
Thanks,
Jim Burns, Indiana U.
ihnp4!inuxa!iuvax!burnsjhc@hou5g.UUCP (Jonathan Clark) (01/15/85)
<> I read a scholarly article about this some little time ago where the point was made that most TV sets are pretty well shielded on the sides and top. Thus the only direction you have to worry about is straight down. Apparently no-one really knows what effect proximity to a monitor will have on videotapes but gradual deterioration of picture quality over a period of months or years is expected. Try standing the monitor on (or lining the videotape compartment of your furniture with) a sheet of aluminium foil if you like - that should stop most of the low-energy EM radiation. Jonathan Clark ATT ISL Holmdel NJ [NAC]!hou5g!jhc
psal@othervax.UUCP (01/21/85)
==== < FOR THE LINE EATER > ==== Aluminium wouldnt be of much use. A shield of grounded mu-metal would, but would be kind of pricey. C.Thomas Weinbaum von Waldenthal
rfg@hound.UUCP (R.GRANTGES) (01/25/85)
[]
>...Aluminum wouldn't be of much use..."
Yes it would. THe problem, I believe, is shielding from ac fields, not
permanent magnetic effects. If so, Aluminum would serve as well and
probably better than the fiendishly expensive mumetal.
--
"It's the thought, if any, that counts!" Dick Grantges hound!rfgnewton2@ucbtopaz.CC.Berkeley.ARPA (01/28/85)
------- The fields are AC, but not EM. Just the near-(inductive)field. Shorting the E-vector doesn't extinguish the (non-propagating) mag flux. Aluminum makes a good electro"static" (Faraday) shield; need something permeable for a mag shield, hence mumetal.
rfg@hound.UUCP (R.GRANTGES) (01/29/85)
[] Eddy currents. -- "It's the thought, if any, that counts!" Dick Grantges hound!rfg