finding orientation with two gps recievers

Hi everyone

Im trying to make a system using two gps recievers to find not position, but orientation eg which way is north. The distance between the two recievers should be less than a meter. Do any of you know how much the relative distance between the two recievers will vary?

I know that in order to get consistent results, the two reciever should get their positional data from the same satellites, but when they are so close, are there any chance that they will choose different satellites?

There are military equipment using this principle to find orientation, so I know it is theoreticaly possible to make this work. What my question is, is wheter I can do this with two common consumer GPSs.