Viavi 87339, Operation Manual

Page: 84 / 198

Testing
4 -3
STEP PROCEDURE
9. Perform the following steps to complete Simulation:
PVT:
Latitude = For Optional entry of test Latitude
Longitude = For Optional entry of test Longitude
Altitude = For Optional entry of test Altitude
10. Select RUN key to start simulation.
11. Select STOP key to discontinue simulation.
NOTE:
Most GPS receivers expect ACTIVE antennas, this means they supply a DC
voltage to the antenna connector. The GPSG-1000 has built in DC voltage
blocking on the GPSG - 1000 TX Port.
NOTE:
Some receivers “sense” current draw on the DC supply to their active antenna.
If there is no current drawn, they may assume that no antenna is connected. In
such cases, the current draw must be simulated by some resistive load and
perhaps a series inductor between the signal line and the ground. Such a device
may need to be custom built, depending on the receiver requirements.
NOTE:
It is recommended that the receiver under test is “cold started” and a fresh
almanac obtained from the GPSG-1000 simulation. This process may take several
minutes, dependent on specific receiver.
NOTE:
Some receivers will not obtain a stable fix when using a simulation time earlier
than the selected almanac. Generally it is best to utilize an almanac that is dated
at least one day before the simulation date.
NOTE:
NOTE: It is important that the receiver under test is not able to receive signals
from the real GPS constellation as the pseudo-ephemeris data of the simulation is
different enough from the real constellation that the mix of data can cause
problems with the receivers positional calculation.
GPS TX PORT: APPLIED DC SHOULD NOT 50 V
C A U T I O N