You'll need to progress through the main story until you reach mission 21 called in search of past glory, where getting a psi-radiation suppressor blueprint to dr dvupalov unlocks this high-end detector. When you hand over the blueprint, you'll get what's probably the most precise artifact detector in the game honestly worth the effort to get.

The veles basically works like a super accurate radar that shows exactly where artifacts and anomalies are hiding with these red directional pings. It's a bit on the heavier side at 0.9kg compared to the echo's 0.4kg, but the precision makes up for it. Something interesting - traders will start stocking it after you complete the mission so don't worry too much if you accidentally sell it or lose it somehow.

A tip that might help - try using both the veles and hilka detectors together since the hilka's got better range but the veles gives you that pinpoint accuracy you'll really want, especially when you're exploring tougher areas like dead city or wandering around pripyat outskirts. Just make sure your game's updated to at least version 1.4.3b, since older versions had some issues with quest rewards in this mission chain.