As far as I know this is in working order, it's been in the loft for some time "in case it was useful" but I don't think it's going to be now.
In essence you run your internet through the mains wiring with this pair of devices so if you've a wifi blank area this is supposed to sort that out for you. I have the manual, two of the devices but only one ethernet cable where the box says two are included, but I imagine you could pick the cable up from somewhere
Passthrough Powerline Port (Fenay Bridge HD8)
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