That's not really what I mean. You don't have to diagnose the signal, just the medium, which can tell you what will happen to the real signal. It requires a f

That's not really what I mean. You don't have to diagnose the signal, just the medium, which can tell you what will happen to the real signal. It requires a fast edge (or a very broadband sweep), but nothing much beyond that. E.g., here's what a bad connector at the far end of an SFF-8654 cable looks like on a TDR: https://i.imgur.com/AiLnSuC.jpeg https://i.imgur.com/AiLnSuC.jpeg . This type of plot can be interpreted as impedance versus distance along the line. It could be made with a small handheld instrument, but currently a human is needed to read the tea leaves. While I was making that measurement, I couldn't help thinking that it would be nice if it didn't require either a 50 GHz VNA or equally-expensive training to read. Equivalent-time sampling gets you out of needing an expensive network analyzer, but it doesn't help with the diagnosis itself. And of course when checking a USB cable you are most likely just after a go/no-go result, not the gory details. That further calls the market economics of such a gadget into question. Still, if somebody offered one at a reasonable price, they'd sell at least one to me.