That's called the Doppler Filter.

So, if an UAV is moving at less than 60-80km/h, it's 'invisible'. ....and then, if one turns the Bayraktar - which can fly as slow as…

That's called the Doppler Filter. Radars are set to ignore/filter out any objects moving at less than 80km/h (or 60km/h etc), in order not to oversaturate pilots/crews with echoes of ground vehicles.

So, if an UAV is moving at less than 60-80km/h, it's 'invisible'. ....and then, if one turns the Bayraktar - which can fly as slow as 40km/h - 'into the wind' (so to create enough uplift under its wings), it's 'standing still' in the air (relative to the ground).