The effect of cryptocurrency mining on LTE spectrum
github.com
github.com
DC continuity is not a good measure of impedance as you move into higher frequency RF signals. Wires that look like low-impedance connections can easily become accidental antennas.
If the motherboard is not connected via metal stems and screws through the holes with an earth ground plane it won’t be grounded this is why there are either solder dots or a copper ring around the screwholes in the motherboard and why you should not use plastic standoffs unless they are explicitly specified and then often if you use metal standoffs you might screw something up.
For mining you essentially connect cards via PCIe raisers which often use a USB 3.0 cable and the card is connected to 12v rails which may or may now lead to earth and often they won’t.
It’s really not that hard to screw it up.
They mention they automate the powder coating of paint. So the external case should be well insulated.
Look at the pictures in the original article. He built his open racks from multiple painted metal parts. The metal parts probably don't provide a solid path to ground. Connecting the ground stake to a big piece of metal that's not grounded adds an antenna to the thing and makes emissions worse.
Easy to fix. Use a Dremel tool and grind off the paint where the stake is screwed into the metal rail. Use jumper wires (properly, green ones) and crimped screw lugs to connect the rails together. Connect those to something that has a grounded case. Check with an ohmmeter to see that there's continuity between the metal cooling plate on the GPU and the ground pin of what plugs into the wall. Should be less than 1 ohm. Use an outlet tester to make sure your wall outlet has a valid ground pin. Now most of your RF hash gets clamped by the tie to ground.
One of my roommates has a computer case with an acrylic window — typical DIY gaming PC case. That window means the case provides poor shielding. When the computer's on, it sputters all over the 70cm ham band.
Ultimately the person/company putting a computer together (or importing it) is responsible for the whole computer adhering to EMI standards.
Do GPUs include a secret "crank everything to 11" test mode feature that exercises all the cores and RAM and everything, so you can just bolt it into a case, maybe connect it to a fake motherboard that supplies 3.3V or whatever so the card initializes properly... or do vendors test with a massive pile of motherboards, measuring and offsetting for the EMI generated by each motherboard?
But now I'm wondering if there are motherboards out there that radiate a little bit more than they should, and force peripheral vendors to do extra work clipping EMI in their own products.
This is probably not true, since all PCI card vendors would have to test their products with tons of different boards.
Attach with Velcro. Also keeps out debris and literal bugs as a side benefit.
The crackdown can't happen soon enough!
Operating graphics cards by the thousands in conditions clearly unfit to operate them likely consitutes at least simple negligence w.r.t. interference that may occur.