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Groups > comp.os.linux.misc > #75070 > unrolled thread
| Started by | c186282 <c186282@nnada.net> |
|---|---|
| First post | 2025-09-24 00:02 -0400 |
| Last post | 2025-09-28 01:00 -0700 |
| Articles | 20 on this page of 180 — 23 participants |
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Floppies - Actual Question c186282 <c186282@nnada.net> - 2025-09-24 00:02 -0400
Re: Floppies - Actual Question Charlie Gibbs <cgibbs@kltpzyxm.invalid> - 2025-09-24 05:06 +0000
Re: Floppies - Actual Question Lawrence D’Oliveiro <ldo@nz.invalid> - 2025-09-24 05:43 +0000
Re: Floppies - Actual Question Stéphane CARPENTIER <sc@fiat-linux.fr> - 2025-09-27 15:21 +0000
Re: Floppies - Actual Question c186282 <c186282@nnada.net> - 2025-09-27 14:17 -0400
Re: Floppies - Actual Question Stéphane CARPENTIER <sc@fiat-linux.fr> - 2025-09-27 22:31 +0000
Re: Floppies - Actual Question Lawrence D’Oliveiro <ldo@nz.invalid> - 2025-09-28 00:26 +0000
Re: Floppies - Actual Question Lawrence D’Oliveiro <ldo@nz.invalid> - 2025-09-28 01:21 +0000
Re: Floppies - Actual Question Stéphane CARPENTIER <sc@fiat-linux.fr> - 2025-09-28 10:21 +0000
Re: Floppies - Actual Question Lawrence D’Oliveiro <ldo@nz.invalid> - 2025-09-28 19:27 +0000
Re: Floppies - Actual Question Stéphane CARPENTIER <sc@fiat-linux.fr> - 2025-10-04 09:37 +0000
Re: Floppies - Actual Question Bobbie Sellers <bliss-sf4ever@dslextreme.com> - 2025-10-04 12:04 -0700
Re: Floppies - Actual Question "Carlos E.R." <robin_listas@es.invalid> - 2025-09-29 14:12 +0200
Re: Floppies - Actual Question Stéphane CARPENTIER <sc@fiat-linux.fr> - 2025-10-04 09:43 +0000
Re: Floppies - Actual Question Rich <rich@example.invalid> - 2025-10-04 15:22 +0000
Re: Floppies - Actual Question Richard Kettlewell <invalid@invalid.invalid> - 2025-10-04 17:38 +0100
Re: Floppies - Actual Question "Carlos E.R." <robin_listas@es.invalid> - 2025-10-04 20:34 +0200
Re: Floppies - Actual Question Stéphane CARPENTIER <sc@fiat-linux.fr> - 2025-10-04 20:53 +0000
Re: Floppies - Actual Question Pancho <Pancho.Jones@protonmail.com> - 2025-10-04 22:56 +0100
Re: Floppies - Actual Question Richard Kettlewell <invalid@invalid.invalid> - 2025-10-05 09:51 +0100
Re: Floppies - Actual Question c186282 <c186282@nnada.net> - 2025-10-06 02:17 -0400
Re: Floppies - Actual Question Pancho <Pancho.Jones@protonmail.com> - 2025-10-07 09:56 +0100
Re: Floppies - Actual Question c186282 <c186282@nnada.net> - 2025-10-08 01:55 -0400
Re: Floppies - Actual Question Pancho <Pancho.Jones@protonmail.com> - 2025-10-08 12:58 +0100
Re: Floppies - Actual Question c186282 <c186282@nnada.net> - 2025-10-09 02:36 -0400
Re: Floppies - Actual Question John Ames <commodorejohn@gmail.com> - 2025-10-08 09:02 -0700
Re: Floppies - Actual Question The Natural Philosopher <tnp@invalid.invalid> - 2025-10-08 17:35 +0100
Re: Floppies - Actual Question "Carlos E.R." <robin_listas@es.invalid> - 2025-10-10 09:29 +0200
Re: Floppies - Actual Question The Natural Philosopher <tnp@invalid.invalid> - 2025-10-10 09:58 +0100
Re: Floppies - Actual Question "Carlos E.R." <robin_listas@es.invalid> - 2025-10-10 13:45 +0200
Re: Floppies - Actual Question The Natural Philosopher <tnp@invalid.invalid> - 2025-10-10 14:02 +0100
Re: Floppies - Actual Question "Carlos E.R." <robin_listas@es.invalid> - 2025-10-10 21:17 +0200
Re: Floppies - Actual Question Lawrence D’Oliveiro <ldo@nz.invalid> - 2025-10-11 00:55 +0000
Re: Floppies - Actual Question c186282 <c186282@nnada.net> - 2025-10-11 02:35 -0400
Partitioning (was Re: Floppies - Actual Question "David W. Hodgins" <dwhodgins@nomail.afraid.org> - 2025-10-08 14:54 -0400
Re: Partitioning (was Re: Floppies - Actual Question Lawrence D’Oliveiro <ldo@nz.invalid> - 2025-10-08 21:15 +0000
Re: Partitioning (was Re: Floppies - Actual Question The Natural Philosopher <tnp@invalid.invalid> - 2025-10-09 12:35 +0100
Re: Floppies - Actual Question Lawrence D’Oliveiro <ldo@nz.invalid> - 2025-10-08 21:13 +0000
Re: Floppies - Actual Question John Ames <commodorejohn@gmail.com> - 2025-10-08 14:29 -0700
Re: Floppies - Actual Question The Natural Philosopher <tnp@invalid.invalid> - 2025-10-09 12:37 +0100
Re: Floppies - Actual Question Rich <rich@example.invalid> - 2025-10-09 15:07 +0000
inodes, customizing partitions "Carlos E.R." <robin_listas@es.invalid> - 2025-10-10 09:45 +0200
Re: inodes, customizing partitions c186282 <c186282@nnada.net> - 2025-10-11 00:57 -0400
Re: inodes, customizing partitions "Carlos E.R." <robin_listas@es.invalid> - 2025-10-11 15:28 +0200
Re: inodes, customizing partitions Nuno Silva <nunojsilva@invalid.invalid> - 2025-10-11 23:46 +0100
Re: inodes, customizing partitions "Carlos E.R." <robin_listas@es.invalid> - 2025-10-12 02:42 +0200
Re: inodes, customizing partitions c186282 <c186282@nnada.net> - 2025-10-13 03:13 -0400
Re: inodes, customizing partitions "Carlos E.R." <robin_listas@es.invalid> - 2025-10-13 10:53 +0200
Re: inodes, customizing partitions c186282 <c186282@nnada.net> - 2025-10-11 22:49 -0400
Re: inodes, customizing partitions c186282 <c186282@nnada.net> - 2025-10-11 21:51 -0400
Re: inodes, customizing partitions c186282 <c186282@nnada.net> - 2025-10-13 03:10 -0400
Re: Floppies - Actual Question John Ames <commodorejohn@gmail.com> - 2025-10-09 09:00 -0700
Re: Floppies - Actual Question c186282 <c186282@nnada.net> - 2025-10-09 21:24 -0400
Re: Floppies - Actual Question The Natural Philosopher <tnp@invalid.invalid> - 2025-10-10 09:52 +0100
Re: Floppies - Actual Question c186282 <c186282@nnada.net> - 2025-10-11 01:45 -0400
Re: Floppies - Actual Question Charlie Gibbs <cgibbs@kltpzyxm.invalid> - 2025-10-11 17:48 +0000
Re: Floppies - Actual Question c186282 <c186282@nnada.net> - 2025-10-11 22:11 -0400
Re: Floppies - Actual Question c186282 <c186282@nnada.net> - 2025-10-09 02:56 -0400
Re: Floppies - Actual Question c186282 <c186282@nnada.net> - 2025-10-09 02:50 -0400
Re: Floppies - Actual Question Lawrence D’Oliveiro <ldo@nz.invalid> - 2025-10-05 20:25 +0000
Re: Floppies - Actual Question "Carlos E.R." <robin_listas@es.invalid> - 2025-10-04 20:35 +0200
Re: Floppies - Actual Question The Natural Philosopher <tnp@invalid.invalid> - 2025-09-28 09:55 +0100
Re: Floppies - Actual Question Richard Kettlewell <invalid@invalid.invalid> - 2025-09-28 11:08 +0100
Re: Floppies - Actual Question Stéphane CARPENTIER <sc@fiat-linux.fr> - 2025-09-28 12:19 +0000
Re: Floppies - Actual Question Richard Kettlewell <invalid@invalid.invalid> - 2025-09-28 15:07 +0100
Re: Floppies - Actual Question The Natural Philosopher <tnp@invalid.invalid> - 2025-09-28 15:36 +0100
Re: Floppies - Actual Question Lawrence D’Oliveiro <ldo@nz.invalid> - 2025-09-28 23:35 +0000
Re: Floppies - Actual Question Charlie Gibbs <cgibbs@kltpzyxm.invalid> - 2025-09-29 00:28 +0000
Re: Floppies - Actual Question c186282 <c186282@nnada.net> - 2025-09-28 21:08 -0400
Re: Floppies - Actual Question Lawrence D’Oliveiro <ldo@nz.invalid> - 2025-09-29 05:31 +0000
Re: Floppies - Actual Question Charlie Gibbs <cgibbs@kltpzyxm.invalid> - 2025-09-29 16:32 +0000
Re: Floppies - Actual Question The Natural Philosopher <tnp@invalid.invalid> - 2025-09-29 18:36 +0100
Re: Floppies - Actual Question Lawrence D’Oliveiro <ldo@nz.invalid> - 2025-09-29 19:30 +0000
Re: Floppies - Actual Question The Natural Philosopher <tnp@invalid.invalid> - 2025-09-29 10:12 +0100
Re: Floppies - Actual Question Lawrence D’Oliveiro <ldo@nz.invalid> - 2025-09-29 19:33 +0000
Re: Floppies - Actual Question candycanearter07 <candycanearter07@candycanearter07.nomail.afraid> - 2025-09-29 19:50 +0000
Re: Floppies - Actual Question The Natural Philosopher <tnp@invalid.invalid> - 2025-09-28 15:31 +0100
Re: Floppies - Actual Question "Carlos E.R." <robin_listas@es.invalid> - 2025-09-29 14:15 +0200
Re: Floppies - Actual Question Bobbie Sellers <bliss-sf4ever@dslextreme.com> - 2025-09-29 08:18 -0700
Re: Floppies - Actual Question Lawrence D’Oliveiro <ldo@nz.invalid> - 2025-09-29 19:27 +0000
Re: Floppies - Actual Question Rich <rich@example.invalid> - 2025-09-28 00:31 +0000
Re: Floppies - Actual Question Nuno Silva <nunojsilva@invalid.invalid> - 2025-09-28 11:19 +0100
Re: Floppies - Actual Question The Natural Philosopher <tnp@invalid.invalid> - 2025-09-28 15:22 +0100
Re: Floppies - Actual Question Charlie Gibbs <cgibbs@kltpzyxm.invalid> - 2025-09-28 18:07 +0000
Re: Floppies - Actual Question Lawrence D’Oliveiro <ldo@nz.invalid> - 2025-09-28 19:18 +0000
Re: Floppies - Actual Question The Natural Philosopher <tnp@invalid.invalid> - 2025-09-28 23:55 +0100
Re: Floppies - Actual Question The Natural Philosopher <tnp@invalid.invalid> - 2025-09-28 09:53 +0100
Re: Floppies - Actual Question Peter 'Shaggy' Haywood <phaywood@alphalink.com.au> - 2025-10-02 18:28 +1000
Re: Floppies - Actual Question Tauno Voipio <tauno.voipio@notused.fi.invalid> - 2025-10-02 21:44 +0300
Re: Floppies - Actual Question Nuno Silva <nunojsilva@invalid.invalid> - 2025-10-03 00:10 +0100
Re: Floppies - Actual Question c186282 <c186282@nnada.net> - 2025-10-03 00:35 -0400
Re: Floppies - Actual Question c186282 <c186282@nnada.net> - 2025-10-03 00:32 -0400
Re: Floppies - Actual Question c186282 <c186282@nnada.net> - 2025-10-03 00:21 -0400
Re: Floppies - Actual Question Peter 'Shaggy' Haywood <phaywood@alphalink.com.au> - 2025-10-04 12:55 +1000
Re: Floppies - Actual Question Andy Burns <usenet@andyburns.uk> - 2025-09-24 06:49 +0100
Re: Floppies - Actual Question The Natural Philosopher <tnp@invalid.invalid> - 2025-09-24 11:45 +0100
Re: Floppies - Actual Question Charlie Gibbs <cgibbs@kltpzyxm.invalid> - 2025-09-24 16:53 +0000
Re: Floppies - Actual Question c186282 <c186282@nnada.net> - 2025-09-24 14:35 -0400
Re: Floppies - Actual Question c186282 <c186282@nnada.net> - 2025-09-24 15:05 -0400
Re: Floppies - Actual Question c186282 <c186282@nnada.net> - 2025-09-24 21:32 -0400
Re: Floppies - Actual Question Lawrence D’Oliveiro <ldo@nz.invalid> - 2025-09-24 20:38 +0000
Re: Floppies - Actual Question rbowman <bowman@montana.com> - 2025-09-25 00:04 +0000
Re: Floppies - Actual Question Robert Riches <spamtrap42@jacob21819.net> - 2025-09-25 00:44 +0000
Re: Floppies - Actual Question c186282 <c186282@nnada.net> - 2025-09-24 20:58 -0400
Re: Floppies - Actual Question "Carlos E.R." <robin_listas@es.invalid> - 2025-09-25 13:07 +0200
Re: Floppies - Actual Question The Natural Philosopher <tnp@invalid.invalid> - 2025-09-25 12:48 +0100
Re: Floppies - Actual Question c186282 <c186282@nnada.net> - 2025-09-25 15:52 -0400
Re: Floppies - Actual Question Lawrence D’Oliveiro <ldo@nz.invalid> - 2025-09-25 22:09 +0000
Re: Floppies - Actual Question The Natural Philosopher <tnp@invalid.invalid> - 2025-09-25 09:44 +0100
Re: Floppies - Actual Question "Carlos E.R." <robin_listas@es.invalid> - 2025-09-25 13:04 +0200
Re: Floppies - Actual Question The Natural Philosopher <tnp@invalid.invalid> - 2025-09-25 12:48 +0100
Re: Floppies - Actual Question "Carlos E.R." <robin_listas@es.invalid> - 2025-09-25 22:15 +0200
Re: Floppies - Actual Question c186282 <c186282@nnada.net> - 2025-09-25 21:06 -0400
Re: Floppies - Actual Question Lawrence D’Oliveiro <ldo@nz.invalid> - 2025-09-25 22:10 +0000
Re: Floppies - Actual Question c186282 <c186282@nnada.net> - 2025-09-25 21:09 -0400
Re: Floppies - Actual Question Lawrence D’Oliveiro <ldo@nz.invalid> - 2025-10-06 22:08 +0000
Re: Floppies - Actual Question c186282 <c186282@nnada.net> - 2025-10-06 23:30 -0400
Re: Floppies - Actual Question Rich <rich@example.invalid> - 2025-10-07 15:16 +0000
Re: Floppies - Actual Question "Carlos E.R." <robin_listas@es.invalid> - 2025-10-08 02:34 +0200
Re: Floppies - Actual Question c186282 <c186282@nnada.net> - 2025-10-08 01:05 -0400
Re: Floppies - Actual Question "Carlos E.R." <robin_listas@es.invalid> - 2025-10-08 10:58 +0200
Re: Floppies - Actual Question The Natural Philosopher <tnp@invalid.invalid> - 2025-10-08 11:06 +0100
Re: Floppies - Actual Question "Carlos E.R." <robin_listas@es.invalid> - 2025-10-08 14:14 +0200
Re: Floppies - Actual Question c186282 <c186282@nnada.net> - 2025-10-09 02:44 -0400
Re: Floppies - Actual Question "Carlos E.R." <robin_listas@es.invalid> - 2025-10-09 21:10 +0200
Re: Floppies - Actual Question c186282 <c186282@nnada.net> - 2025-10-09 21:36 -0400
Re: Floppies - Actual Question The Natural Philosopher <tnp@invalid.invalid> - 2025-10-10 09:54 +0100
Re: Floppies - Actual Question c186282 <c186282@nnada.net> - 2025-10-11 01:57 -0400
Re: Floppies - Actual Question "Carlos E.R." <robin_listas@es.invalid> - 2025-10-10 13:49 +0200
Re: Floppies - Actual Question c186282 <c186282@nnada.net> - 2025-10-11 02:29 -0400
Re: Floppies - Actual Question "Carlos E.R." <robin_listas@es.invalid> - 2025-10-11 14:32 +0200
Re: Floppies - Actual Question Joerg Walther <joerg.walther@magenta.de> - 2025-10-09 12:50 +0200
Re: Floppies - Actual Question "Carlos E.R." <robin_listas@es.invalid> - 2025-10-09 21:11 +0200
Re: Floppies - Actual Question c186282 <c186282@nnada.net> - 2025-10-09 21:37 -0400
Re: Floppies - Actual Question Joerg Walther <joerg.walther@magenta.de> - 2025-10-10 11:19 +0200
Phone wallet "Carlos E.R." <robin_listas@es.invalid> - 2025-10-10 13:51 +0200
Re: Phone wallet c186282 <c186282@nnada.net> - 2025-10-11 02:30 -0400
Re: Phone wallet "Carlos E.R." <robin_listas@es.invalid> - 2025-10-11 14:32 +0200
Re: Phone wallet c186282 <c186282@nnada.net> - 2025-10-11 21:35 -0400
Re: Phone wallet "Carlos E.R." <robin_listas@es.invalid> - 2025-10-12 14:48 +0200
Re: Floppies - Actual Question c186282 <c186282@nnada.net> - 2025-10-09 21:17 -0400
Re: Floppies - Actual Question Charlie Gibbs <cgibbs@kltpzyxm.invalid> - 2025-10-10 06:51 +0000
Re: Floppies - Actual Question c186282 <c186282@nnada.net> - 2025-10-10 03:29 -0400
Re: Floppies - Actual Question The Natural Philosopher <tnp@invalid.invalid> - 2025-10-10 09:55 +0100
Re: Floppies - Actual Question c186282 <c186282@nnada.net> - 2025-10-11 02:10 -0400
Re: Floppies - Actual Question The Natural Philosopher <tnp@invalid.invalid> - 2025-10-08 13:18 +0100
Re: Floppies - Actual Question Robert Riches <spamtrap42@jacob21819.net> - 2025-10-09 03:09 +0000
Re: Floppies - Actual Question c186282 <c186282@nnada.net> - 2025-10-09 02:58 -0400
Re: Floppies - Actual Question The Natural Philosopher <tnp@invalid.invalid> - 2025-10-09 12:45 +0100
Re: Floppies - Actual Question Robert Riches <spamtrap42@jacob21819.net> - 2025-10-10 02:53 +0000
Re: Floppies - Actual Question c186282 <c186282@nnada.net> - 2025-10-09 23:44 -0400
Re: Floppies - Actual Question c186282 <c186282@nnada.net> - 2025-10-09 02:45 -0400
Re: Floppies - Actual Question c186282 <c186282@nnada.net> - 2025-10-09 02:38 -0400
Re: Floppies - Actual Question Rich <rich@example.invalid> - 2025-10-09 15:16 +0000
Faraday cages (was: Re: Floppies - Actual Question) Nuno Silva <nunojsilva@invalid.invalid> - 2025-10-09 17:02 +0100
Re: Faraday cages Rich <rich@example.invalid> - 2025-10-09 18:48 +0000
Re: Faraday cages The Natural Philosopher <tnp@invalid.invalid> - 2025-10-10 09:49 +0100
Re: Floppies - Actual Question The Natural Philosopher <tnp@invalid.invalid> - 2025-10-10 09:47 +0100
Re: Floppies - Actual Question c186282 <c186282@nnada.net> - 2025-10-11 01:05 -0400
Re: Floppies - Actual Question c186282 <c186282@nnada.net> - 2025-10-08 01:52 -0400
Re: Floppies - Actual Question c186282 <c186282@nnada.net> - 2025-10-08 01:38 -0400
Re: Floppies - Actual Question c186282 <c186282@nnada.net> - 2025-09-24 20:45 -0400
Re: Floppies - Actual Question rbowman <bowman@montana.com> - 2025-09-25 05:27 +0000
Re: Floppies - Actual Question c186282 <c186282@nnada.net> - 2025-09-25 15:42 -0400
Re: Floppies - Actual Question rbowman <bowman@montana.com> - 2025-09-26 04:59 +0000
Re: Floppies - Actual Question c186282 <c186282@nnada.net> - 2025-09-26 01:36 -0400
Re: Floppies - Actual Question The Natural Philosopher <tnp@invalid.invalid> - 2025-09-27 09:12 +0100
Re: Floppies - Actual Question c186282 <c186282@nnada.net> - 2025-09-27 13:58 -0400
Re: Floppies - Actual Question c186282 <c186282@nnada.net> - 2025-09-27 03:11 -0400
Re: Floppies - Actual Question "Carlos E.R." <robin_listas@es.invalid> - 2025-09-29 14:22 +0200
Re: Floppies - Actual Question c186282 <c186282@nnada.net> - 2025-09-29 23:03 -0400
Re: Floppies - Actual Question "Carlos E.R." <robin_listas@es.invalid> - 2025-09-30 09:32 +0200
Re: Floppies - Actual Question Rich <rich@example.invalid> - 2025-09-26 15:19 +0000
Re: Floppies - Actual Question c186282 <c186282@nnada.net> - 2025-09-24 20:23 -0400
Re: Floppies - Actual Question The Natural Philosopher <tnp@invalid.invalid> - 2025-09-25 09:45 +0100
Re: Floppies - Actual Question Marco Moock <mm@dorfdsl.de> - 2025-09-24 08:41 +0200
Re: Floppies - Actual Question "Carlos E.R." <robin_listas@es.invalid> - 2025-09-24 12:04 +0200
Re: Floppies - Actual Question c186282 <c186282@nnada.net> - 2025-09-24 14:34 -0400
Re: Floppies - Actual Question John McCue <jmclnx@SPAMisBADgmail.com> - 2025-09-24 17:11 +0000
Re: Floppies - Actual Question Daniel <me@sc1f1dan.com> - 2025-09-28 01:00 -0700
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| From | Lawrence D’Oliveiro <ldo@nz.invalid> |
|---|---|
| Date | 2025-09-24 20:38 +0000 |
| Message-ID | <10b1krp$3tbca$4@dont-email.me> |
| In reply to | #75111 |
On Wed, 24 Sep 2025 16:53:00 GMT, Charlie Gibbs wrote: > On 2025-09-24, The Natural Philosopher <tnp@invalid.invalid> wrote: > >> Reformatting *at a low level* should work however. >> Its so long I cannot remember how to do that. > > First you get a large magnet... I remember a friend describing a test that was done with those huge magnets that are used to pick up cars in wrecking yards. It was used to grab a bunch of magnetic tape reels. The tapes read perfectly fine afterwards. An oscillating magnetic field, on the other hand, like you got with CRT monitors, also speakers ...
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| From | rbowman <bowman@montana.com> |
|---|---|
| Date | 2025-09-25 00:04 +0000 |
| Message-ID | <mjjf90Ftbb2U5@mid.individual.net> |
| In reply to | #75126 |
On Wed, 24 Sep 2025 20:38:17 -0000 (UTC), Lawrence D’Oliveiro wrote: > An oscillating magnetic field, on the other hand, like you got with CRT > monitors, also speakers ... I was wondering what a degaussing coil would do.
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| From | Robert Riches <spamtrap42@jacob21819.net> |
|---|---|
| Date | 2025-09-25 00:44 +0000 |
| Message-ID | <slrn10d943v.aj5.spamtrap42@one.localnet> |
| In reply to | #75144 |
On 2025-09-25, rbowman <bowman@montana.com> wrote: > On Wed, 24 Sep 2025 20:38:17 -0000 (UTC), Lawrence D’Oliveiro wrote: > >> An oscillating magnetic field, on the other hand, like you got with CRT >> monitors, also speakers ... > > I was wondering what a degaussing coil would do. Degaussing coils were intended to demagnetize the ferrous metal pieces around a CRT. I'd guess it would probably erase at least some magnetic media. When I worked at a TV station around 1980, we had a bulk tape eraser that would do a fairly decent job on 2" wide quadaplex tape. With tape of that width, it was necessary to do both sides of the reel. The erasure wasn't complete, because the field could not reach the middle of the tape. It wasn't a big surprise that the aluminum reel would not block the effect. Remodeling the core of a large power transformer from a tube-type TV can create a bulk tape eraser strong enough for 1/4" audio tape. However, I haven't used it in long enough that I don't remember exactly where it is. Then, there's an apocryphal story about a DEC field service guy who put a tape in briefcase and rode the subway to the customer's location only to find the tape unreadable. Reportedly, putting the briefcase on the floor of the subway got it too close to the magnetic fields of the subway car's motors. Reportedly, the solution was to take a taxi rather than the subway. HTH -- Robert Riches spamtrap42@jacob21819.net (Yes, that is one of my email addresses.)
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| From | c186282 <c186282@nnada.net> |
|---|---|
| Date | 2025-09-24 20:58 -0400 |
| Message-ID | <FwWdnUVvLosKDkn1nZ2dnZfqn_WdnZ2d@giganews.com> |
| In reply to | #75151 |
On 9/24/25 20:44, Robert Riches wrote: > On 2025-09-25, rbowman <bowman@montana.com> wrote: >> On Wed, 24 Sep 2025 20:38:17 -0000 (UTC), Lawrence D’Oliveiro wrote: >> >>> An oscillating magnetic field, on the other hand, like you got with CRT >>> monitors, also speakers ... >> >> I was wondering what a degaussing coil would do. > > Degaussing coils were intended to demagnetize the ferrous metal > pieces around a CRT. I'd guess it would probably erase at least > some magnetic media. When COLOR TVs came into the picture it was sometimes necessary to degauss the shadow mask, which often did include some iron in the alloy. Once had a huge lightning bolt pass over my house and hit a nearby tree. My TV was suddenly all weird colors. A tech brought a degaussing coil - all fixed. > When I worked at a TV station around 1980, we had a bulk tape > eraser that would do a fairly decent job on 2" wide quadaplex > tape. With tape of that width, it was necessary to do both sides > of the reel. The erasure wasn't complete, because the field > could not reach the middle of the tape. It wasn't a big surprise > that the aluminum reel would not block the effect. Tape that wide, yea, it would be hard to get a simple coil to put a good field all the way through ... you'd need a 'bar' magnet and rotate the tape under it. > Remodeling the core of a large power transformer from a tube-type > TV can create a bulk tape eraser strong enough for 1/4" audio > tape. However, I haven't used it in long enough that I don't > remember exactly where it is. There used to be bulk erasers for VHS tapes - but that's only half-inch. > Then, there's an apocryphal story about a DEC field service guy > who put a tape in briefcase and rode the subway to the customer's > location only to find the tape unreadable. Reportedly, putting > the briefcase on the floor of the subway got it too close to the > magnetic fields of the subway car's motors. Reportedly, the > solution was to take a taxi rather than the subway. Ummm ... MIGHT just be a cautionary "story". I'd think there is enough iron in subway cars to absorb/dissipate anything coming off the motors underneath.
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| From | "Carlos E.R." <robin_listas@es.invalid> |
|---|---|
| Date | 2025-09-25 13:07 +0200 |
| Message-ID | <jckfqlxilj.ln2@Telcontar.valinor> |
| In reply to | #75153 |
On 2025-09-25 02:58, c186282 wrote: > On 9/24/25 20:44, Robert Riches wrote: >> On 2025-09-25, rbowman <bowman@montana.com> wrote: >>> On Wed, 24 Sep 2025 20:38:17 -0000 (UTC), Lawrence D’Oliveiro wrote: >>> >>>> An oscillating magnetic field, on the other hand, like you got with CRT >>>> monitors, also speakers ... >>> >>> I was wondering what a degaussing coil would do. >> >> Degaussing coils were intended to demagnetize the ferrous metal >> pieces around a CRT. I'd guess it would probably erase at least >> some magnetic media. > > When COLOR TVs came into the picture it was sometimes > necessary to degauss the shadow mask, which often did > include some iron in the alloy. Once had a huge lightning > bolt pass over my house and hit a nearby tree. My TV was > suddenly all weird colors. A tech brought a degaussing > coil - all fixed. Many TVs or computer displays did a degausing at some instant during power up or off, before it displayed anything. -- Cheers, Carlos. ES🇪🇸, EU🇪🇺;
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| From | The Natural Philosopher <tnp@invalid.invalid> |
|---|---|
| Date | 2025-09-25 12:48 +0100 |
| Message-ID | <10b3a6u$8nn9$3@dont-email.me> |
| In reply to | #75186 |
On 25/09/2025 12:07, Carlos E.R. wrote: > On 2025-09-25 02:58, c186282 wrote: >> On 9/24/25 20:44, Robert Riches wrote: >>> On 2025-09-25, rbowman <bowman@montana.com> wrote: >>>> On Wed, 24 Sep 2025 20:38:17 -0000 (UTC), Lawrence D’Oliveiro wrote: >>>> >>>>> An oscillating magnetic field, on the other hand, like you got with >>>>> CRT >>>>> monitors, also speakers ... >>>> >>>> I was wondering what a degaussing coil would do. >>> >>> Degaussing coils were intended to demagnetize the ferrous metal >>> pieces around a CRT. I'd guess it would probably erase at least >>> some magnetic media. >> >> When COLOR TVs came into the picture it was sometimes >> necessary to degauss the shadow mask, which often did >> include some iron in the alloy. Once had a huge lightning >> bolt pass over my house and hit a nearby tree. My TV was >> suddenly all weird colors. A tech brought a degaussing >> coil - all fixed. > > Many TVs or computer displays did a degaussing at some instant during > power up or off, before it displayed anything. > > > All of them did. -- "And if the blind lead the blind, both shall fall into the ditch". Gospel of St. Mathew 15:14
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| From | c186282 <c186282@nnada.net> |
|---|---|
| Date | 2025-09-25 15:52 -0400 |
| Message-ID | <vUmdnYJRCv4bAEj1nZ2dnZfqnPGdnZ2d@giganews.com> |
| In reply to | #75186 |
On 9/25/25 07:07, Carlos E.R. wrote: > On 2025-09-25 02:58, c186282 wrote: >> On 9/24/25 20:44, Robert Riches wrote: >>> On 2025-09-25, rbowman <bowman@montana.com> wrote: >>>> On Wed, 24 Sep 2025 20:38:17 -0000 (UTC), Lawrence D’Oliveiro wrote: >>>> >>>>> An oscillating magnetic field, on the other hand, like you got with >>>>> CRT >>>>> monitors, also speakers ... >>>> >>>> I was wondering what a degaussing coil would do. >>> >>> Degaussing coils were intended to demagnetize the ferrous metal >>> pieces around a CRT. I'd guess it would probably erase at least >>> some magnetic media. >> >> When COLOR TVs came into the picture it was sometimes >> necessary to degauss the shadow mask, which often did >> include some iron in the alloy. Once had a huge lightning >> bolt pass over my house and hit a nearby tree. My TV was >> suddenly all weird colors. A tech brought a degaussing >> coil - all fixed. > > Many TVs or computer displays did a degausing at some instant during > power up or off, before it displayed anything. Yep ... but the field created by the bolt was too intense for the inbuilt degausser to fix. Had to bring in the big gun, so to speak. Anyway, the TV continued to work well for another ten years after.
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| From | Lawrence D’Oliveiro <ldo@nz.invalid> |
|---|---|
| Date | 2025-09-25 22:09 +0000 |
| Message-ID | <10b4ej2$jqe8$4@dont-email.me> |
| In reply to | #75186 |
On Thu, 25 Sep 2025 13:07:31 +0200, Carlos E.R. wrote: > Many TVs or computer displays did a degausing at some instant during > power up or off, before it displayed anything. I can remember the first time I (and my colleagues) encountered the legendary Apple 13” RGB monitor, in 1987. This was built around a Sony Trinitron tube (itself a legend of the CRT days). It was the first colour monitor we had seen that was so good, you could use it as a black-and- white monitor and not notice it could do colour. In other words, it didn’t sacrifice text readability for colour capability. (Hard for the young folks to believe, I know, but such a compromise was all too common in those days.) Every time you switched it on, it emitted a loud “thump” noise. I don’t think this was actually the degaussing: that was activated by a separate button, and all it made was a “click” sound.
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| From | The Natural Philosopher <tnp@invalid.invalid> |
|---|---|
| Date | 2025-09-25 09:44 +0100 |
| Message-ID | <10b2vdc$5u19$9@dont-email.me> |
| In reply to | #75151 |
On 25/09/2025 01:44, Robert Riches wrote: > Degaussing coils were intended to demagnetize the ferrous metal > pieces around a CRT. I'd guess it would probably erase at least > some magnetic media. Back in the day the death rate of floppy disks kept in storage boxes next to the CRT monitor was impressive -- "I guess a rattlesnake ain't risponsible fer bein' a rattlesnake, but ah puts mah heel on um jess the same if'n I catches him around mah chillun".
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| From | "Carlos E.R." <robin_listas@es.invalid> |
|---|---|
| Date | 2025-09-25 13:04 +0200 |
| Message-ID | <r7kfqlxilj.ln2@Telcontar.valinor> |
| In reply to | #75151 |
On 2025-09-25 02:44, Robert Riches wrote: > On 2025-09-25, rbowman <bowman@montana.com> wrote: >> On Wed, 24 Sep 2025 20:38:17 -0000 (UTC), Lawrence D’Oliveiro wrote: ... > Then, there's an apocryphal story about a DEC field service guy > who put a tape in briefcase and rode the subway to the customer's > location only to find the tape unreadable. Reportedly, putting > the briefcase on the floor of the subway got it too close to the > magnetic fields of the subway car's motors. Reportedly, the > solution was to take a taxi rather than the subway. At some point in the 80's, a friend at uni wanted to go home with his floppies kept safe (the train was electric). We told him to try wrapping in aluminum kitchen foil, or perhaps in a cookie tin box. I don't remember what he did exactly, but it worked. If you are interested I can ask him. -- Cheers, Carlos. ES🇪🇸, EU🇪🇺;
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| From | The Natural Philosopher <tnp@invalid.invalid> |
|---|---|
| Date | 2025-09-25 12:48 +0100 |
| Message-ID | <10b3a5u$8nn9$2@dont-email.me> |
| In reply to | #75184 |
On 25/09/2025 12:04, Carlos E.R. wrote: > On 2025-09-25 02:44, Robert Riches wrote: >> On 2025-09-25, rbowman <bowman@montana.com> wrote: >>> On Wed, 24 Sep 2025 20:38:17 -0000 (UTC), Lawrence D’Oliveiro wrote: > > ... > >> Then, there's an apocryphal story about a DEC field service guy >> who put a tape in briefcase and rode the subway to the customer's >> location only to find the tape unreadable. Reportedly, putting >> the briefcase on the floor of the subway got it too close to the >> magnetic fields of the subway car's motors. Reportedly, the >> solution was to take a taxi rather than the subway. > > At some point in the 80's, a friend at uni wanted to go home with his > floppies kept safe (the train was electric). We told him to try wrapping > in aluminum kitchen foil, or perhaps in a cookie tin box. I don't > remember what he did exactly, but it worked. If you are interested I can > ask him. > Tinfoil does not block magnetic fields, Only µ-metal does that. Or distance. Iron is a help too -- "And if the blind lead the blind, both shall fall into the ditch". Gospel of St. Mathew 15:14
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| From | "Carlos E.R." <robin_listas@es.invalid> |
|---|---|
| Date | 2025-09-25 22:15 +0200 |
| Message-ID | <5gkgqlx61n.ln2@Telcontar.valinor> |
| In reply to | #75193 |
On 2025-09-25 13:48, The Natural Philosopher wrote: > On 25/09/2025 12:04, Carlos E.R. wrote: >> On 2025-09-25 02:44, Robert Riches wrote: >>> On 2025-09-25, rbowman <bowman@montana.com> wrote: >>>> On Wed, 24 Sep 2025 20:38:17 -0000 (UTC), Lawrence D’Oliveiro wrote: >> >> ... >> >>> Then, there's an apocryphal story about a DEC field service guy >>> who put a tape in briefcase and rode the subway to the customer's >>> location only to find the tape unreadable. Reportedly, putting >>> the briefcase on the floor of the subway got it too close to the >>> magnetic fields of the subway car's motors. Reportedly, the >>> solution was to take a taxi rather than the subway. >> >> At some point in the 80's, a friend at uni wanted to go home with his >> floppies kept safe (the train was electric). We told him to try >> wrapping in aluminum kitchen foil, or perhaps in a cookie tin box. I >> don't remember what he did exactly, but it worked. If you are >> interested I can ask him. >> > Tinfoil does not block magnetic fields, Only µ-metal does that. Or > distance. Iron is a help too Cookie tins are made of iron. Partially, at least. -- Cheers, Carlos. ES🇪🇸, EU🇪🇺;
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| From | c186282 <c186282@nnada.net> |
|---|---|
| Date | 2025-09-25 21:06 -0400 |
| Message-ID | <NLqdnbr4z8aKekj1nZ2dnZfqn_adnZ2d@giganews.com> |
| In reply to | #75242 |
On 9/25/25 16:15, Carlos E.R. wrote: > On 2025-09-25 13:48, The Natural Philosopher wrote: >> On 25/09/2025 12:04, Carlos E.R. wrote: >>> On 2025-09-25 02:44, Robert Riches wrote: >>>> On 2025-09-25, rbowman <bowman@montana.com> wrote: >>>>> On Wed, 24 Sep 2025 20:38:17 -0000 (UTC), Lawrence D’Oliveiro wrote: >>> >>> ... >>> >>>> Then, there's an apocryphal story about a DEC field service guy >>>> who put a tape in briefcase and rode the subway to the customer's >>>> location only to find the tape unreadable. Reportedly, putting >>>> the briefcase on the floor of the subway got it too close to the >>>> magnetic fields of the subway car's motors. Reportedly, the >>>> solution was to take a taxi rather than the subway. >>> >>> At some point in the 80's, a friend at uni wanted to go home with his >>> floppies kept safe (the train was electric). We told him to try >>> wrapping in aluminum kitchen foil, or perhaps in a cookie tin box. I >>> don't remember what he did exactly, but it worked. If you are >>> interested I can ask him. >>> >> Tinfoil does not block magnetic fields, Only µ-metal does that. Or >> distance. Iron is a help too > > Cookie tins are made of iron. Partially, at least. Yep, considerable improvement. Haven't seen mu-metal at the local superstore ... though WalMart DOES list it online. Did see some, MIGHT have bought some, from a surplus store however. Amazon SOMETIMES has sheets in stock.
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| From | Lawrence D’Oliveiro <ldo@nz.invalid> |
|---|---|
| Date | 2025-09-25 22:10 +0000 |
| Message-ID | <10b4ekb$jqe8$5@dont-email.me> |
| In reply to | #75184 |
On Thu, 25 Sep 2025 13:04:59 +0200, Carlos E.R. wrote: > At some point in the 80's, a friend at uni wanted to go home with his > floppies kept safe (the train was electric). We told him to try wrapping > in aluminum kitchen foil, or perhaps in a cookie tin box. I don't > remember what he did exactly, but it worked. “Faraday cage”.
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| From | c186282 <c186282@nnada.net> |
|---|---|
| Date | 2025-09-25 21:09 -0400 |
| Message-ID | <6tmdnfU90LA4ekj1nZ2dnZfqn_GdnZ2d@giganews.com> |
| In reply to | #75250 |
On 9/25/25 18:10, Lawrence D’Oliveiro wrote: > On Thu, 25 Sep 2025 13:04:59 +0200, Carlos E.R. wrote: > >> At some point in the 80's, a friend at uni wanted to go home with his >> floppies kept safe (the train was electric). We told him to try wrapping >> in aluminum kitchen foil, or perhaps in a cookie tin box. I don't >> remember what he did exactly, but it worked. > > “Faraday cage”. A Faraday cage is fair at shielding from electric fields and some EM radiation ... but not magnetic. For that you need iron or mu-metal.
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| From | Lawrence D’Oliveiro <ldo@nz.invalid> |
|---|---|
| Date | 2025-10-06 22:08 +0000 |
| Message-ID | <10c1ekm$ivvt$7@dont-email.me> |
| In reply to | #75250 |
On 6 Oct 2025 10:29:47 GMT, Stefan Ram wrote: > Lawrence =?iso-8859-13?q?D=FFOliveiro?= <ldo@nz.invalid> wrote or > quoted: >> >>On Thu, 25 Sep 2025 13:04:59 +0200, Carlos E.R. wrote: >>> >>> At some point in the 80's, a friend at uni wanted to go home with >>> his floppies kept safe (the train was electric). We told him to >>> try wrapping in aluminum kitchen foil, or perhaps in a cookie tin >>> box. I don't remember what he did exactly, but it worked. >> >> “Faraday cage”. > > And it seems that, in practice, a Faraday cage can possibly protect > to some extend against fast changing magnetic fields, but less > against slowly changing magnetic fields. Good enough. Don’t forget to give your pet AI a tip.
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| From | c186282 <c186282@nnada.net> |
|---|---|
| Date | 2025-10-06 23:30 -0400 |
| Message-ID | <v0-dnQ5xTdrtFHn1nZ2dnZfqn_adnZ2d@giganews.com> |
| In reply to | #75250 |
On 10/6/25 06:29, Stefan Ram wrote: > Lawrence =?iso-8859-13?q?D=FFOliveiro?= <ldo@nz.invalid> wrote or quoted: >> On Thu, 25 Sep 2025 13:04:59 +0200, Carlos E.R. wrote: >>> At some point in the 80's, a friend at uni wanted to go home with his >>> floppies kept safe (the train was electric). We told him to try wrapping >>> in aluminum kitchen foil, or perhaps in a cookie tin box. I don't >>> remember what he did exactly, but it worked. >> “Faraday cage”. > > In a perfect conductor, inside the material itself (such as > the cage walls), the electric field E is zero because free > charges move to cancel any applied electric field. > > Faraday's law then implies that within the conductor, the magnetic > field B cannot be changing with time. > > Changing magnetic fields induce currents (eddy currents). > These induced currents generate opposing magnetic fields > that cancel the time-varying components inside the conductor, > effectively shielding against changing magnetic fields. > > But this does not imply zero magnetic field inside the conductor's > hollow interior (the cage's interior space). Static fields do not > induce currents because there is no changing magnetic flux within > the conductor to generate an electromotive force. Consequently, > these magnetic fields penetrate the cage interior unaffected. > > Also, real materials might not be perfect conductors. And it > seems that, in practice, a Faraday cage can possibly protect > to some extend against fast changing magnetic fields, but less > against slowly changing magnetic fields. It would take a fairly extreme static/slow-changing field to erase floppies. You can do it - I just did a couple weeks ago - using a neo magnet at point blank range - but fields from train motors, I just don't see it. High-frequency mag fields are more dangerous but even THEN would need to be pretty strong. My guess is that we're hearing an "urban legend" here. As for metal boxes ... they can mostly absorb electric/EM and fast-changing mag fields (if iron) - but they're not perfect with mag fields. There WILL be a field inside the box ... you can test it, the devices necessary are pretty cheap. Hell, try a 50-cent compass and a tiny hole for looking through. This sort of thing becomes of strategic interest when it comes to protecting mil tech against EMP attack. Designing devices meant to be put into vehicles and/or with cheapo little motors some years ago the MAIN issue was strong electrical noise caused by engine ignition systems. Actual magnetic was not a real thing. SOME input filtering and, most useful for the job, OPTO- ISOLATORS solved my problems. Optos require CURRENT to light up - but electrical noise doesn't have enough. Not good for high-SPEED connections though.
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| From | Rich <rich@example.invalid> |
|---|---|
| Date | 2025-10-07 15:16 +0000 |
| Message-ID | <10c3arg$111ce$1@dont-email.me> |
| In reply to | #75744 |
c186282 <c186282@nnada.net> wrote: > On 10/6/25 06:29, Stefan Ram wrote: >> Lawrence =?iso-8859-13?q?D=FFOliveiro?= <ldo@nz.invalid> wrote or quoted: >>> On Thu, 25 Sep 2025 13:04:59 +0200, Carlos E.R. wrote: >>>> At some point in the 80's, a friend at uni wanted to go home with >>>> his floppies kept safe (the train was electric). We told him to >>>> try wrapping in aluminum kitchen foil, or perhaps in a cookie tin >>>> box. I don't remember what he did exactly, but it worked. >>>> “Faraday cage”. >> >> In a perfect conductor, inside the material itself (such as the >> cage walls), the electric field E is zero because free charges >> move to cancel any applied electric field. >> >> Faraday's law then implies that within the conductor, the >> magnetic field B cannot be changing with time. >> >> Changing magnetic fields induce currents (eddy currents). These >> induced currents generate opposing magnetic fields that cancel >> the time-varying components inside the conductor, effectively >> shielding against changing magnetic fields. >> >> But this does not imply zero magnetic field inside the >> conductor's hollow interior (the cage's interior space). Static >> fields do not induce currents because there is no changing >> magnetic flux within the conductor to generate an electromotive >> force. Consequently, these magnetic fields penetrate the cage >> interior unaffected. >> >> Also, real materials might not be perfect conductors. And it >> seems that, in practice, a Faraday cage can possibly protect to >> some extend against fast changing magnetic fields, but less >> against slowly changing magnetic fields. > > It would take a fairly extreme static/slow-changing > field to erase floppies. You can do it - I just did > a couple weeks ago - using a neo magnet at point blank > range - but fields from train motors, I just don't > see it. High-frequency mag fields are more dangerous > but even THEN would need to be pretty strong. The drop off of magnetic field intensity by distance can be **approximated** as 1/(d^3) (inverse cube drop). So yes, the field from the train motors would need to be extremely strong, or the OP's floppies would have had to be very close to the motors, for the electric train motors to have any impact on the floppies. > My guess is that we're hearing an "urban legend" > here. Yes. There are a lot of those that go around. And since the "foil wrap" did nothing, but the floppies were undamaged (and the person did not do an A-B test with some wrapped, some unwrapped) they delude themselves into belieiving the foil wrap actually did something.
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| From | "Carlos E.R." <robin_listas@es.invalid> |
|---|---|
| Date | 2025-10-08 02:34 +0200 |
| Message-ID | <95ogrlxsru.ln2@Telcontar.valinor> |
| In reply to | #75766 |
On 2025-10-07 17:16, Rich wrote: > c186282 <c186282@nnada.net> wrote: >> On 10/6/25 06:29, Stefan Ram wrote: >>> Lawrence =?iso-8859-13?q?D=FFOliveiro?= <ldo@nz.invalid> wrote or quoted: >>>> On Thu, 25 Sep 2025 13:04:59 +0200, Carlos E.R. wrote: >>>>> At some point in the 80's, a friend at uni wanted to go home with >>>>> his floppies kept safe (the train was electric). We told him to >>>>> try wrapping in aluminum kitchen foil, or perhaps in a cookie tin >>>>> box. I don't remember what he did exactly, but it worked. >>>>> “Faraday cage”. >>> >>> In a perfect conductor, inside the material itself (such as the >>> cage walls), the electric field E is zero because free charges >>> move to cancel any applied electric field. >>> >>> Faraday's law then implies that within the conductor, the >>> magnetic field B cannot be changing with time. >>> >>> Changing magnetic fields induce currents (eddy currents). These >>> induced currents generate opposing magnetic fields that cancel >>> the time-varying components inside the conductor, effectively >>> shielding against changing magnetic fields. >>> >>> But this does not imply zero magnetic field inside the >>> conductor's hollow interior (the cage's interior space). Static >>> fields do not induce currents because there is no changing >>> magnetic flux within the conductor to generate an electromotive >>> force. Consequently, these magnetic fields penetrate the cage >>> interior unaffected. >>> >>> Also, real materials might not be perfect conductors. And it >>> seems that, in practice, a Faraday cage can possibly protect to >>> some extend against fast changing magnetic fields, but less >>> against slowly changing magnetic fields. >> >> It would take a fairly extreme static/slow-changing >> field to erase floppies. You can do it - I just did >> a couple weeks ago - using a neo magnet at point blank >> range - but fields from train motors, I just don't >> see it. High-frequency mag fields are more dangerous >> but even THEN would need to be pretty strong. > > The drop off of magnetic field intensity by distance can be > **approximated** as 1/(d^3) (inverse cube drop). So yes, the field > from the train motors would need to be extremely strong, or the OP's > floppies would have had to be very close to the motors, for the > electric train motors to have any impact on the floppies. Well, some trains have motors on every carriage. Then also there was the thought that the overhead cable carried large currents and perhaps produced large fields. It was just the fear that something might happen to the floppies, and what should we do to prevent hypothetical damage. We had no experience, and there was no internet to ask other people. > >> My guess is that we're hearing an "urban legend" >> here. > > Yes. There are a lot of those that go around. And since the "foil > wrap" did nothing, but the floppies were undamaged (and the person did > not do an A-B test with some wrapped, some unwrapped) they delude > themselves into belieiving the foil wrap actually did something. I don't remember if we used just foil, or a tin box, or both. Also, I don't remember if there was another floppy outside. I might ask the other chap if you people are that interested. -- Cheers, Carlos. ES🇪🇸, EU🇪🇺;
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| From | c186282 <c186282@nnada.net> |
|---|---|
| Date | 2025-10-08 01:05 -0400 |
| Message-ID | <af-dncNqL6mEbHj1nZ2dnZfqn_adnZ2d@giganews.com> |
| In reply to | #75771 |
On 10/7/25 20:34, Carlos E.R. wrote: > On 2025-10-07 17:16, Rich wrote: >> c186282 <c186282@nnada.net> wrote: >>> On 10/6/25 06:29, Stefan Ram wrote: >>>> Lawrence =?iso-8859-13?q?D=FFOliveiro?= <ldo@nz.invalid> wrote or >>>> quoted: >>>>> On Thu, 25 Sep 2025 13:04:59 +0200, Carlos E.R. wrote: >>>>>> At some point in the 80's, a friend at uni wanted to go home with >>>>>> his floppies kept safe (the train was electric). We told him to >>>>>> try wrapping in aluminum kitchen foil, or perhaps in a cookie tin >>>>>> box. I don't remember what he did exactly, but it worked. >>>>>> “Faraday cage”. >>>> >>>> In a perfect conductor, inside the material itself (such as the >>>> cage walls), the electric field E is zero because free charges >>>> move to cancel any applied electric field. >>>> >>>> Faraday's law then implies that within the conductor, the >>>> magnetic field B cannot be changing with time. >>>> >>>> Changing magnetic fields induce currents (eddy currents). These >>>> induced currents generate opposing magnetic fields that cancel >>>> the time-varying components inside the conductor, effectively >>>> shielding against changing magnetic fields. >>>> >>>> But this does not imply zero magnetic field inside the >>>> conductor's hollow interior (the cage's interior space). Static >>>> fields do not induce currents because there is no changing >>>> magnetic flux within the conductor to generate an electromotive >>>> force. Consequently, these magnetic fields penetrate the cage >>>> interior unaffected. >>>> >>>> Also, real materials might not be perfect conductors. And it >>>> seems that, in practice, a Faraday cage can possibly protect to >>>> some extend against fast changing magnetic fields, but less >>>> against slowly changing magnetic fields. >>> >>> It would take a fairly extreme static/slow-changing >>> field to erase floppies. You can do it - I just did >>> a couple weeks ago - using a neo magnet at point blank >>> range - but fields from train motors, I just don't >>> see it. High-frequency mag fields are more dangerous >>> but even THEN would need to be pretty strong. >> >> The drop off of magnetic field intensity by distance can be >> **approximated** as 1/(d^3) (inverse cube drop). So yes, the field >> from the train motors would need to be extremely strong, or the OP's >> floppies would have had to be very close to the motors, for the >> electric train motors to have any impact on the floppies. > > Well, some trains have motors on every carriage. Then also there was the > thought that the overhead cable carried large currents and perhaps > produced large fields. > > It was just the fear that something might happen to the floppies, and > what should we do to prevent hypothetical damage. We had no experience, > and there was no internet to ask other people. > > >> >>> My guess is that we're hearing an "urban legend" >>> here. >> >> Yes. There are a lot of those that go around. And since the "foil >> wrap" did nothing, but the floppies were undamaged (and the person did >> not do an A-B test with some wrapped, some unwrapped) they delude >> themselves into belieiving the foil wrap actually did something. > > I don't remember if we used just foil, or a tin box, or both. Also, I > don't remember if there was another floppy outside. I might ask the > other chap if you people are that interested. SOME precautions are logical, esp when the level of danger is unclear. However train motors/feeds ... sorry, just can't see it. The fields would be much too small. The train body also acts as protection. The field needed to erase a floppy ... it'd also fatally magnetize mechanical watches and such and erase audio tapes. Remember when music came on cassette tapes, you paid $$$ for those. The neo mag I used to 'clear' a mis-sectored floppy is, at point-blank range, EXTREME. You don't want to get your finger between two of those. Before the tariffs you could buy 6x4x2-inch neo mags polarized across the z axis. Don't know HOW you'd get those off anything they stuck to. They all came with warning messages. If your hand was in the way it'd be literally pulped. I have a stack of 25x12mm discs - indeed it's two stacks of 6 to 8. I keep them separated by attracting each other thru a 3/4" shelf board. So, floppies/tapes/hdds erasing ... I'm still going to put it down as an old "urban legend". High freqs, 400hz and a bit above, are best for erasing magnetic media. The reversing field does not have time to solidify a new bias in the media. The best scheme is to start with a large field and then taper. For "destruction" 50/60hz will do ok.
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