Re: Floppies - Actual Question

From	Robert Riches <spamtrap42@jacob21819.net>
Newsgroups	comp.os.linux.misc
Subject	Re: Floppies - Actual Question
Date	2025-10-10 02:53 +0000
Organization	none-at-all
Message-ID	<slrn10egt97.tgq.spamtrap42@one.localnet> (permalink)
References	(14 earlier) <umlhrlxmm6.ln2@Telcontar.valinor> <cards-20251008130855@ram.dialup.fu-berlin.de> <10c5kqp$1j0pj$1@dont-email.me> <slrn10ee9rk.7di.spamtrap42@one.localnet> <10c8788$2kf2m$6@dont-email.me>

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On 2025-10-09, The Natural Philosopher <tnp@invalid.invalid> wrote:
> On 09/10/2025 04:09, Robert Riches wrote:
>> On 2025-10-08, The Natural Philosopher <tnp@invalid.invalid> wrote:
>>> On 08/10/2025 13:10, Stefan Ram wrote:
>>>> "Carlos E.R." <robin_listas@es.invalid> wrote or quoted:
>>>>> There was no urban legend in those years, floppies were a recent
>>>>> invention. We simply did not know. We invented the urban legends.
>>>>
>>>>     Some people around here are walking around with those
>>>>     RFID cards today, and they're thinking about wrapping
>>>>     them in aluminum foil to make it harder to scan them.
>>>>
>>>>
>>> That may well be true
>> 
>> Did the test.
>> 
>> My second-to-most-recent emplyer had NFC/RFID badge cards that
>> each employee was required to scan at the lobby when entering a
>> facility.  For the test of one of the metal-lined sleeves, I
>> asked the "guard" at the desk for permission to test the sleeve
>> by doing an experiment to see whether the ID badge card could be
>> read while inside the sleeve.  The "guard" said he would watch
>> his monitor while I attempted to scan the sleeved badge card.  He
>> said his system could not see that the badge card existed while
>> it was in the sleeve.  Outside the sleeve, the badge card worked
>> perfectly.
>> 
>> Based on that test, it appears that sleeve was sufficient to
>> sheild at least the type of NFC/RFID used in that badge card.
>> 
> Good. My time designing radios inside tin boxes was not wasted then!
> Irrelevant factoid. Back when I was involved in professional RF design, 
> there was a rule of thumb, which more or less said 'you will never get a 
> design stable unless it has less gain that 20 dB per inch of separation 
> between stages'. It was surprisingly accurate. But then we started 
> needing to pack all this stuff into small guided missiles, and as the 
> parts got smaller so did the permissible separation. Then we started 
> building little tin walls round each stage and got it even smaller...and 
> when ICs game along they were so small that the radiation coupling 
> between input and output was soi low that they could cram 60dB into a 
> single chip.
>
> Tinfoil blocks RF. Juts come to my house which uses foil backed 
> plasterboard everywhere. we ordered some for the bathrooms and over 
> ordered so we used it everywhere.
> Cant get a wifi signal from one room to another at all.

On a house, aluminum siding also attenuates (US bands) AM (and I
think FM) broadcast radio.  A couple of decades ago, I lived in a
house with aluminum siding.  Enough signal got through to listen,
but the SNR was not as good as it would have been without the
aluminum.

On a little different angle of RF oddities, in a house without
aluminum siding but possibly with foil-backed fiberglass
insulation in the exterior walls, my Casio G-Shock watch (near
Portland, Oregon, USA) had great difficulty receiving the 60kHz
signal from WWVB.  Even outdoors, reception was not very
reliable.  However, ever since getting Comcast Xfinity internet
over coax, indoor reception is fairly close to flawless.  Most
nights, it sets at 12:03am, which is the best possible case.  My
hunch is the above-ground (pun not intended) TV distribution
system and the coax from the utility pole to the house act as a
passive antenna booster for the watch.

-- 
Robert Riches
spamtrap42@jacob21819.net
(Yes, that is one of my email addresses.)

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Re: Floppies - Actual Question ram@zedat.fu-berlin.de (Stefan Ram) - 2025-10-06 10:29 +0000
  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 ram@zedat.fu-berlin.de (Stefan Ram) - 2025-10-08 12:10 +0000
              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

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