How to generate GPS signal continuous

Question

Hi,
I encountered a problem recently and I need your help. A customer used a PXI-5671 to generate GPS signals to test a receiver. The problem was like this:
1) When we used actual GPS signals instead of simulated signals generated from the PXI-5671, the receiver functioned normally.
2) When we streamed bin file to generate signals repeatedly using the PXI-5671, the receiver could receive correctly for the first time, while at the rest of it the receiver couldn't receive the signals nor display how many satellites there were and what the signal strengths were.
I supposed, that this was due to the reason that the timestamp for the second time was earlier than that at previous time. How do we generate GPS signals continuously with the timestamps updated?

Answer 1

Hi,
When you stram from a bin file repeatedly, it will run first time but will lose lock because when it comes tothe beginning of the file, its time suddenly jumps and the receiver does not accept this. For example, lets say your bin file is from GPS time t1=0 to GPS time t2=30000s. When you loop back around the file, the time increases from 0 to 30000 and then jumps back to 0 and that is not acceptable by receiver. You will need a direct streaming from 5671.
I can put that up for you soon if you want.
Regards, 
Sastry 
Sastry Vadlamani
RF and Communications Software R&D
National Instruments