I find radar in general to be pretty much a waste of time in SH3.
As was pointed out, in foul weather, when you need it most, it keeps cutting out when water hits it.
But with map contacts turned off, it's next to useless. It's very difficult to get a contact to show on the oscilloscope when you actually have visual contact of the target. I don't think I was ever able to use the radar manually successfully in a combat environment. I think by the time you got it to work you'd have broadcast your position many times over.
The Type XXI is supposed to have a PPI indicator (like this:
) but it still has the old style oscilloscope display.
Steve