Second connector is MCX
I've actually bought one of these recently to use for our main TV which is hooked up to a Mac mini. The second input does actually use a coax cable, but the plug on the end is an MCX plug, which is a bit unusual. Even Maplins didn't have any appropriate adapter, but there is a guy in Hong Kong who is selling adapters on ebay that a lot of people have recommended (search ebay for "RF Coaxial to MCX Plug Antenna Rooftop Adaptor DVB-T" to find them).
Alternatively there is the quick and dirty method which is to simply cut the cable of the supplied secondary antenna and solder that to a coax cable with a normal RF connector on the other end. That's what I did and it's fairly easy. I just used a splitter then to take the feed from our roof and then plugged that into both inputs. Then I was getting great signal for both tuners and the dual tuner mode works marvellously.