This is a true RF isolation transformer which is rather hard to find - from a DC point of view it completely isolates the ground/earth connection of the input from the output side and can be used to 'break' the hum loop problems sometimes encountered with complex audio-visual installations, where multiple earthing points in the system can cause an annoying 50Hz hum. The Axing TZU 10-00 is a much better alternative to home-made bodge-ups involving 2 capacitors and a coax plug & socket since it preserves the 75ohm impedance matching throughout and ensures minimum insertion loss to the RF signal.

It's a well-made sealed unit in what appears to be a corrosion-resistant casing that simply plugs into a TV, FM radio or DAB radio co-ax socket with whatever is being fed with signal from it plugging into the outlet socket. It works fine with both a direct signal from a TV aerial and with the amplified signal from an aerial distribution system.