@Geojoek I've run "floating" stations many times. I'm doing it right now. (Second floor, very old house, no grounds anywhere to be found). If you ignore DC grounding / lightning protection, I wouldn't bother with a common grounding bus-bar or earth ground. It will work fine if and only if what's at the far end of the coax is matched and absorbs or radiates all the RF that the transmitter sends up the coax. If not, and RF is coming back on the shield of the coax, you'll have problems ranging from RF burns to computer upsets. As an extra measure I usually use a "coax choke balun" at the shack end of the coax. This is usually some number of turns, like 8, on an FT240-43 toroid to choke off any small amounts of RF that the coax shield might pick up by radiation from the antenna. I also use FT-140-43 cores around the shack on mouse, keyboard, video, headphone, USB cables to catch any stray RF and to stop those devices from interfering with the radio.