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Comment by superkuh | Hacker News Reader

Computers used to come in proper full metal cases. Now they don't. Even when you try to find a metal case for a personal build most cases have giant holes in the side (case windows) acting as slot antennas. And plastic case laptop designs are even worse. Radiated emissions are much easier to achieve at useful intensities these days because of it. Sure, before the conductors going in and out radiated somewhat effectively (and still do). But now even core system components inside are just being let emit without any mitigation.

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I have my computer in a metal box because it has caught fire twice.

Ignoring the obvious "dmd is truly blazing fast" quip, wildly curious how this happened to you twice? Was it the PSU? Only once heard of a house fire caused by a computer, but no information on component actually caused it.

The first time it was the graphics card. It burst into flames and smoke poured out. The fire went out when I yanked the power. Fortunately, I was sitting next to it when it went. To be fair, it was doing a long graphics job.

After that, I set the computer on a metal plate to keep a fire from spreading to the floor.

Some years later, the PSU went out with a bang and a lot of smoke.

(dmd is so fast, the computer doesn't have time to heat up!)

i'm guessing some overclocking was involved, maybe some dust.

> most cases have giant holes in the side (case windows) acting as slot antennas.

They won't act as slot antennas unless they are tuned to the frequency you wish to transmit on, and actually electrically connected on each side to your transmitter.

Correct. But also, an antenna doesn't have to be exactly resonant at the desired frequency in order to help. You can see this most often in the antennas people use for HF, which to be resonant have to be giant and many meters in size, but instead they use small non-resonant antenna that still transmit enough, even at very low efficiency, to radiate an annoying amount of interference.

Not having a giant slot antenna is a lot better than having a slot antenna. Even if the slot antenna is best resonant at mid-VHF (ie, ~144 MHz which is what many GPU RAMs are blasting at at high current).

And just as important: a huge hole is a hole. Even if it's not acting as an efficient antenna. It's basically an entire side of the case missing.

Well, exactly. It's acting as a huge hole, it's not acting in any way as an antenna.

To work as a slot antenna you'd have to have a low impedance feed right into the middle of each side of the hole, and for 144MHz the sides of your PC would need to be about 2.5 metres along each edge.

You're talking about being right on resonance as if it won't help if it's off by 20% of the center frequency. But that's not true. Just like you can use a stumpy monopole whip for 144 Mhz even though it's 6 inches long, and it will help significantly (but behave like an omni capacitive reactance element), so will this not quite right slot antenna mode. There are many ways to excite and feed a slot antenna that do not depend on having the two excitation terminals on each side of the slot. Especially if you're doing it off frequency. Any conductor in the near field is going to couple via induction.

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