Hall 5 radar... how does it exactly work?

I’ve some questions about the halo 5 radar. Sometimes i see the enemy on the radar when he is near but sometimes not. When do you activate the radar? When you shoot, spartan charge, thrust or even sprint? I don’t know. Can someone explain this to me? Thank you guys

If i’m not wrong, you’re visible on the radar when you move to fast (faster than crounch position allow you to move) and when you shoot.