BR1 Positioning question



We have a vechicle installation with a MAX BR1. In the same vehicle we also have a TETRA radio unit.
Both of these has an external antenna on the roof of the car.
However, somtimes there are adverse conditions and the radio loses the GPS signal, but the BR1 unit still reports position data.
Since it seems unaffected by this, does MAX BR1 use any other satellite system (GLONASS or Galileo) to aggregate position data?



I think it is just GPS