They would definitely have to be using the same frequency to work properly together. That would be the first clue.

You could just be receiving interference because of the proximity of the unit and sensor while you are testing. To test that it is working properly you would have to install the computer and sensors in their proper positions and compare the results over a known distance.

Why don't you specify the computer brand and model sensor combinations you want to use instead of calling them A and B. Maybe someone has some experience but does not want to play 20 questions with you finding out the computers you have.