Hello there, QRZers. Resorting to the Community Knowledge. Scenario: FT-991A. Without a computer connected to it, just the radio and the antenna, IPO (no preamps), letting it gaily be, I have a nearly silent band. Less than S1 of background noise (red annotation). You can even see a AM QSO at around 3600 (green annotation). Good stuff, right? Almost. This is the story when I connect the USB cable to the computer: Well. Not so. Almost 6 S-units of background noise and... Where's that QSO around 3600? Engulfed by QRM. Life's hard, right? ¯\_(ツ)_/¯ The 80m band is the worst case scenario, the most badly affected band. Other bands suffers mildly or not affected. SO. Solutions. The first thing I thought about was a USB isolator. But it can only handle up to 12 Mbps of traffic (see https://www.digikey.com/products/en/isolators/digital-isolators/901?k=usb isolator). And honestly, with audio full duplex plus the CAT interface, I'm unsure it would be a good solution - I suspect that the USB traffic might surpass this 12 Mbps limit. Darn. Then, I thought about the good old ferrite choke trick. Actually, this cable already sports two built-in ferrite chokes, one at each end. After thinking a bit more, I realized that the shielding (where the choke blocks any interference), bonds together with the ground power line that runs inside the USB cable inside the radio, BEFORE a ferrite bead. See below: SO, yay, the ferrite might filter out whatever signal is picked by the external shield, but the QRM travels undisturbed and safely through the USB ground lead, safe and sound, protected by the external shielding. Another (maybe) relevant piece of information. If I remove the antenna cable, connecting or disconnecting the USB port has no effect - it stays S0. However, if the antenna is connected, by just touching the USB cable at the USB port, then it spews the QRM. Any ideas to tackle that out? Or is my understanding 100% plain wrong, wrong, wrong as Krusty Olde Kurt used to write? Appreciate your analysis & comment. - Rodrigo.