Re: Is the mains 'earth' good enough?
Mains earth is for safety, not RF earthing. Nowadays it's very noisy. Even modern equipment can be designed to might safety regulations and have a metal cabinet and yet have no Earth via mains plug.
Never disconnect an earth wire on three wire flex.
Anything that needs an external aerial has either a signal return (balanced or coaxial cable to dipole etc) or needs an earth wire to an outdoor ground spike at least as the "mains" Earth is too noisy.
If it's a two core flex isolated flex, just connect the Earth wire direct. You may want a ferrite choke on mains cable. But that doesn't work well at MW/LW. See below.
If it's a 3 core flex, put a few ferrite chokes on mains cable or 5 to 10 turns of entire cable on an old LOPT core and isolate aerial and earth sockets with 1nF 1000V ceramic capacitors, at the radio.
Water pipes are not reliable anymore as an earth. One galvanised steel 4' (1.2m) earth spike from Electrical wholesale and 4mm wire to it is a minimum. A number of spikes around the garden (more the better) tied together is even better.
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