[HN Gopher] RF Shielding History: When the FCC Cracked Down on C...
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RF Shielding History: When the FCC Cracked Down on Computers
Author : shortformblog
Score : 49 points
Date : 2025-10-21 14:26 UTC (8 hours ago)
(HTM) web link (tedium.co)
(TXT) w3m dump (tedium.co)
| superkuh wrote:
| I wish the FCC would go back to doing their job re: radio
| interference and unintentional emissions. The entire concept of a
| computer case 'window' is about equally as anti-social and rude
| as littering in a public park. But it's so pervasive and socially
| accepted when I bring it up the only responses I receive are all
| quite hostile. Even worse are the computer builds that don't have
| any metal case at all. They're broadcasting that <30 MHz
| interference from the high speed switching electronics around the
| world, ruining a shared medium for everyone, and they have no
| idea.
|
| And really, it's not the consumer's place to be aware of these
| things. It's the regulators'. And they've dropped the ball.
| transpute wrote:
| _> computer builds that don 't have any metal case at all_
|
| Would be nice to have more metal cases for SBCs, like the one
| on R4S, https://www.androidpimp.com/embedded/nanopi-r4s-review
|
| KKSB makes metal cases for some SBCs, https://kksb-cases.com
| superkuh wrote:
| I run a handful of odroid sbcs constantly with 3x rtl-sdr usb
| radio receivers each. For their cases I used the cardboard
| box they shipped in covered in overlapping 2" conductive-glue
| backed copper tape. And lots of type/mix 63 ferrites on the
| cords.
| oakwhiz wrote:
| Metallized windows would be nice at least
| transpute wrote:
| One workaround is conductive mesh (metal/fabric) over the
| window interior, bridged to bare metal of the case interior.
| dontlaugh wrote:
| I also don't get the point. Why would you want to look inside
| your PC or even have lots of coloured lights in it to look at?
| sokoloff wrote:
| I think the insides of a PC look more interesting than a flat
| piece of sheet metal. Adding addressable LEDs make that even
| more true.
|
| Visually, I don't care particularly much one way or the
| other, but on a 6-12 layer PCB, there's plenty of opportunity
| to closely couple and shield fast-changing signals, so I
| wouldn't expect surrounding in a Faraday cage would be needed
| (and certainly I've never noticed an issue from the computers
| near my RF receivers).
| dontlaugh wrote:
| Neither is very visible under your desk, except for
| possibly the front of the case.
|
| I went out of my way to avoid extra lights, which sadly
| wasn't possible for the GPU. I had to figure out how to
| turn those off in software.
| afandian wrote:
| I'd heard, probably in a Centre for Computing History [0]
| interview or similar that these regulations contributed to the
| BBC Micro never getting a good foothold in the USA and losing to
| Apple.
|
| It had an amazing selection of ports, all unshielded and designed
| for flat ribbon cables. But that wouldn't fly in the USA.
|
| [0] https://www.youtube.com/@ComputinghistoryOrgUk1
| jaydenmilne wrote:
| Tangentially related: once I bought a no name Amazon HDMI switch
| that would cause FM interference but only when the screen was
| mostly white: https://youtu.be/n2DPLEvwO-k
|
| Another reason to use dark mode I guess
| mmastrac wrote:
| What's interesting is that HDMI is supposed to have a
| scrambling system that prevents any repeating pattern from
| causing EMI. I wonder if there was an unshielded, unscrambled
| raw data path somewhere in the switch.
| EvanAnderson wrote:
| Ahh, alternative futures...
|
| If the FCC hadn't been so strict I think there's a good chance
| we'd be using computers with a lineage going back to Atari versus
| IBM today.
|
| Commodore ate Atari's lunch with the C64 and pricing, but Atari
| could have launched the 400/800 at lower price points with more
| lax emission standards. They would have had lower peripheral
| price points, too, since the SIO bus and "smart peripheral"
| design was also an emissions strategy.
|
| On the home computer front the Atari 8-bits beat the pants off of
| the PET for graphics and sound capabilities. More success in the
| late 70s might have enabled Atari to build down to a price point
| that would have prevented the C64 from even happening.
|
| On the business side Atari R&D had interesting stuff going on (a
| Unix workstation, Transputer machines). Alan Kay even worked
| there! They were thinking about business computing. If the 8-bits
| had had more success I think more interesting future products
| could have been brought to market on the revenue they generated.
| fidotron wrote:
| > If the FCC hadn't been so strict I think there's a good
| chance we'd be using computers with a lineage going back to
| Atari versus IBM today.
|
| And/or many of the other manufacturers of that era. I have
| encountered execs from that era that still believe the whole
| thing was some sort of shrouded protectionism.
| squeedles wrote:
| I happened to buy an Atari 800 at the peak of this and was
| amazed at the metal castings that surrounded everything. That
| little 6502 could survive small arms fire! That shielding was
| far beyond anything else at the time.
|
| And you make a good point about the SIO bus - this was when
| every other machine had unshielded ribbon cables everywhere.
| Their devotion to daisy chained serial really crippled them in
| terms of speed, and when USB finally arrived, I initially
| scorned it due to the prejudice formed by my experience with
| the Atari peripherals! It turns out they were on the right
| track all along!
| EvanAnderson wrote:
| You may not be aware, but Joe DeCuir, who worked for Atari on
| the VCS and 8-bit computers, also worked on the development
| of USB. Some of his Atari engineering notes helped fend off a
| patent troll who tried to claim USB was infringing. It's a
| neat story. There are a ton of interviews with him about it.
| He gave a nice presentation at VCF a few years ago where it
| was mentioned, too: https://youtube.com/watch?v=dlVpu_QSHyw
| mmastrac wrote:
| For those of you who watch Adrian Black on YouTube, you might
| remember him angrily tearing out RF shielding from the older
| computers.
|
| On the other hand, I have been struggling to get my IP KVM at
| home working and it turned out that the cause of its failure was
| some cheap PoE extractors that spew noise across the spectrum,
| especially interfering with VGA sync.
|
| Modern equipment, assuming you aren't buying bargain-basement
| AliExpress junk (which I do, from time to time) is surprisingly
| good at RF rejection.
|
| And, amusingly, this just popped up on Twitter:
| https://x.com/hakluke/status/1980479234159398989
| anjel wrote:
| Back in the mid-century, we used to put an AM radio anywhere on
| the same desk next to the TRS-80 and the revealed cacophany was
| endlessly fascinating. As I recall, radio tuning was unnecessary.
| whartung wrote:
| We used to put them next to our TI-58/59 calculators. You could
| use the radio for sound effects in games.
| bitwize wrote:
| The first application developed for the MITS Altair, besides
| watching the blinkenlights blink, was playing music on a
| nearby AM radio.
| schoen wrote:
| I remember being confused as a kid about the "this device must
| accept any interference received, including interference that may
| cause undesired operation" labels.
|
| I kept reading "must accept" as a technical requirement, somehow
| like "must not be shielded against" or "must not use technical
| means to protect against", rather than what I now think is the
| intended legal sense "does not have any legal recourse against".
|
| It's weird that they phrased it in terms of how the device itself
| must "accept" the interference, rather than the _owner_ accepting
| it.
| bitwize wrote:
| I always thought it meant "must continue to function despite"
| such interference, i.e., it must not blow up or break
| permanently in the presence of such interference.
| transpute wrote:
| _" Using Deep Learning to Eavesdrop on HDMI from its Unintended
| Electromagnetic Emanations"_ (2024),
| https://news.ycombinator.com/item?id=41116682
|
| _" Tempest-LoRa: Cross-Technology Covert Communication via HDMI
| RF Emissions"_, https://news.ycombinator.com/item?id=44483262
| whartung wrote:
| Anecdotes from the age.
|
| When I would fire up my KIM-1, the TV would turn to snow.
|
| There was a toy called the "Big Trak", a programmable ATV toy. If
| you ran that underneath the desk with a TRS-80 on it, it would
| crash.
|
| The TRS-80 Model 1 was notorious for this, as you connected the
| computer to the expansion interface with a bare, 40(? ish?) pin
| ribbon connector. It was a beautiful broadcast antenna for
| computer signals.
|
| The FCC was an impetus for the Model 3.
| MountDoom wrote:
| The regulatory landscape here is pretty funny. In all likelihood,
| the worst RFI offenders in your home are LED lights, followed by
| major appliances. Both of these are regulated less than something
| like a computer mouse. For lightbulbs, I think the manufacturers
| just self-certify.
|
| I guess there are two ways to look at it. Either the regulation
| was wildly successful, so the problems persist only in the less-
| regulated spaces. Or we spend a lot of effort chasing the wrong
| problem.
| Flamingoat wrote:
| If I turn my kettle or microwave on in my kitchen it will kill
| any bleutooth or wifi signal. My microwave is getting on for 15
| years old, maybe newer ones are better, but the kettle was
| bought last year.
| elevation wrote:
| If you cannot change the microwave, consider trying a
| different wifi channel. I once had a 2012 Panasonic microwave
| that killed 802.11g channels 7 and 14 but not channel 0.
| FuriouslyAdrift wrote:
| Microwave ovens hover in and around the 2.4 GHz range just
| like 802.11b/g. Switching to 5 or 6 GHz
| (802.11a/n/ac/ax/etc) - can help immensely.
| Flamingoat wrote:
| I am not too bothered about it. I only use it every other
| day for about 3 minutes to heat up some porridge. I keep on
| meaning to buy a new Microwave, I bought it in ASDA 15
| years ago for PS30 and it just keeps on working.
| jcalvinowens wrote:
| The worst RFI I encounter in my day to day life is from ethernet
| switches... I really wish the FCC would stop allowing the use of
| 125.0MHz on airband. My local airport (KPAO) uses that as it's
| ground frequency, and it's every bit as terrible as you'd expect
| :D
| alwa wrote:
| I was gratified by the last little tidbit: a nod to the Ohio
| "tinkerer" whose 2019 experiment in home automation interfered
| with neighbors' 315MHz-band devices to the point that the power
| company shut off the whole block in an attempt to isolate the
| interference
|
| https://www.nytimes.com/2019/05/04/us/key-fobs-north-olmsted...
|
| (https://archive.is/aTWZ2)
|
| Apparently the regulations work well enough to provoke an
| official response when garage door openers stop working over the
| area of a few houses... a level of reliability I'd long taken for
| granted
| mrandish wrote:
| Having lived through the early 8-bit home computer era as a
| teenaged user and then in the mid-80s working in tech startups
| making hardware peripherals for 16-bit computers - although not
| as a hardware designer, here's my perspective. Early digital
| devices definitely could occasionally cause interference with TVs
| and radios in their immediate area, so there needed to be some
| regulation to address the issue.
|
| However, once aware of the potential problems it wasn't too hard
| or even very expensive to design hardware which avoided the most
| serious problems. Properly grounding components and a little bit
| of light shielding here and there would generally suffice to
| ensure most devices wouldn't cause noticeable issues more than
| two walls and 30 feet away. I think by the 90s the vast majority
| of hardware designers knew how to mitigate these issues while the
| evolution of consumer device speeds and designs reduced the risks
| of actual interference on both the 'interferor' and 'interferee'
| sides.
|
| Unfortunately, the FCC's regulatory testing requirements didn't
| similarly evolve. Hardware designers I worked with described an
| opaque process of submitting a product for FCC testing only to
| receive a "Pass/Fail" with no transparency into how it was
| tested. Sometimes the exact same physical product could be
| resubmitted a month later with zero changes and pass. This made
| things unpredictable and slow, which could be a lethal
| combination for small hardware startups. So there emerged a sub-
| industry of "independent RF testing labs" which you could pay to
| use their pricey gear and claimed expertise to test your device
| and tell you why it failed, let you make a change right there and
| retest again until you passed. This made things more predictable
| but it could cost upwards of $10K (in 90s dollars) which was a
| serious hardship for garage startups. I was told a lot of the
| minor hardware changes made during such interactive testing
| probably did nothing to decrease actual interference in the real-
| world and only served to pass the test.
|
| Then came the era of "weaponizing" FCC certification. Small
| startups could avoid the costs and delay of FCC testing by filing
| their product as a "Class A" device (which meant only for use in
| industrial/scientific environments) instead of as a "Class B"
| (consumer) device. The devices still had to not interfere but
| their makers could self-certify their internal tests without
| going through FCC testing. When new hardware startups would
| threaten a large, established company product with a cheaper,
| better product shipped as "Class A", BigCo would report them
| either interfering or just being used in consumer environments -
| despite the device very likely not interfering with anything.
| This ended up creating a lot of problems for such startups
| because if their cool new product ended up even once in an
| arguably "retail distribution channel", they could get hit with
| big fines - all without ever causing any actual interference -
| and even if the device was able to pass FCC testing and _would_
| have been certified as Class B. It got especially ridiculous when
| a lot of cheaper products were simply generic designs, like a
| modem using the standard Rockwell chip set and reference design.
| These were often made on the same production line and even used
| the same circuit board in a different case as other products
| which all passed FCC testing. But if you didn 't have your
| official "FCC Cert", you could get busted.
|
| I left the hardware space in the early 2000s so I never heard if
| these regs were ever modernized, but it sure seemed like they
| were in need of it.
| bji9jhff wrote:
| I like how you described how I imagine OSA will be used.
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