Wouldn't that answer the topic question with a resounding "Not very good"? The strategypage front page has a article on it; should be somewhat informative.

If the firefinder is forcing the attacking mortar teams to come in closer, then it is very useful. Its existence denies the attackers the safest ground, the areas from which they might easily escape after attacking, the areas where they can get to more easily and unnoticed, by which I mean those areas which are furthest from the target. If it can do that, then it sounds like a fantastic success.

First the article is misleading/badly written because it implies that the radar needs line of sight to the baseplate. This, of course, is untrue Firefinder is not a ground surveillance radar, it has to track the projectile in flight for a few seconds, and flight could be either the up or down part of the trajectory. There are actually a couple issues here. First, is the mortar in the radar's arc when it fires? If not then someone has to tell the radar where to look, keep the mortar time of flight short and by the time the radar is looking in the right direction the bombs have probably impacted. Next is the question of whether or not the radar is switched on, some of these systems aren't too good at running 24x7 for weeks on end, and what the warm up time is like. More likely the radars may be kept in a standby mode that allows quick transition to full power, but they still have to point in the right direction, getting all-round coverage would need several radars and I suspect the US Army has nowhere near enough radars to do this for every base in Iraq. However, if attacks only ever come from one direction you don't need all round radar cover. Interestingly the Brits don't seem to be having this problem, although they are receiving bombs and rockets. They use a very modern radar (MAMBA AKA ArtHur) that is designed for continuous operation against guns, mortars and rockets) but it still has a limited arc. Interestingly when they went North last year they didn't take MAMBA with them, instead they took ASP. ASP is a fully developed version of HALO that was first used very succesfully in the Balkans. It uses sound ranging not radar, this means it's passive and provides all round coverage. It also seems that it can also be programmed to pick up and discriminate between all sorts of weapon firing. Interestingly it's been reported that in 2003 in acquired Iraqi guns at almost 60km range. The Brit approach seems to be to use ASP to locate and then dispatch a QRF. Ground surveillance radar would enable you to spot suspicious activity (given line of sight), whether it would spot a firing mortar would depend on its mode (GSRs often use doppler) and the velocity range that is searched for (usually men, animals, vehicles and helicopters, which are mostly slower that mortar bombs).

there is good article in the latest FA journal about this subject, specific to the counter mortar fight in Mosul(i think). one of the major problems is time; a good example is this- 3 guys drive around until they are ready to fire, a guy opens the back door and fires a couple of rounds, then they're off. not very accurate, they aim towards a base camp and hope it hits something. i think you can access FA jounal on the Ft. Sill website.

Of course rockets are even more tricky, set them up on 'field expedient' (eg bits of timber) launchers and use a timer to fire them when the preparation party is well away. I think it was the VC who first did this, I'm also fairly sure it was used by the Adoo in Oman, and no doubt others elsewhere.