Today as I was driving, I came up behind one of those "Your Speed Is:" signs from the back. My V1 gave me fairly OK warning that I was coming towards it. On my way back, the V1 alerted me appropriately as I was now heading straight towards the front of the sign. After I passed it though, the alert quickly died out. No real arrows pointing backwards.
It seems, then, that the front antenna is much more sensitive, I'd guess because of size, than the rear. The front did pick up the weak signal from the rear of the sign, whereas the back antenna really couldn't.
Does this have some implications about how to interpret rear alerts? When you're getting a rear signal, it must be fairly strong if it's lighting up the rear arrow. Right?