Probably shouldn't have your decoder in the attic anyway, as they aren't well suppressed in terms of EM interference which will seep into the antenna. Particularly a cheap AC-DC wall wart, they're basically broad-spectrum noise-jammers.
I shunt the USB output of the SSR dongles onto Ethernet and pipe that to the PC downstairs.
Huh? It’s ADSB 1090 MHz on a short run of coax to a FlightAware SDR USB dongle. It’s an urban environment so I don’t expect much but I receive plenty of aircraft over 300 nm. Any further away and I would have loss due to inherent limitations of the coax. I could go with like LMR400 but I am not going to spend that kind of money or add like a LNA. This is a setup people commonly use
I shunt the USB output of the SSR dongles onto Ethernet and pipe that to the PC downstairs.