Mine's called a Nova TD-500. The 'D' is for the optional (windows-only) diversity mode, whereby it has a second aerial input and both tuners join forces to give the best signal on a single channel. When not used in 'D' mode, you just use the top socket, the second one seems be pretty much open-circuit and (I've tried) contributes no signal.
The 'D' was all I could find at the time and, before I bought it I did much googling, and found conflicting answers about whether or not it was similar to a T-500, and whether or not it would work in bog-standard Linux. Apart from sensitivity however, it actually worked a treat, straight out of the box. There's supposed to be option for the T-500 to enable a 'low noise amplifier', but it seems to have zero effect with the 'D', there seems to be general agreement on that in the forums.
The circumstances in which mine struggles the most is when both tuners are on the same multiplex, at which point occasional pixelisation becomes continuous. I imagine that each tuner has a tuned circuit that resonates its load at the frequency being received, and when both tuners are loading the same frequency at the same time, there's just not enough signal to keep them both happy