Viavi 87339, Operation Manual

Page: 95 / 198

Testing
4 -14
4.1.7.B Acquisition (warm start)
The receiver has some almanac information that is less than one week old but does not
have any ephemeris information.
NOTE:
Ephemeris information is only valid for 4 hrs. Typically, the receiver knows the
time to within 20 seconds and the position to within 100 km. Most modern GPS
receivers achieve a position fix from a warm condition in less than 60 seconds but
can sometimes achieve a position fix in much less time.
Perform the following steps for Acquisition (warm start) TTF measurement.
STEP PROCEDURE
1, If connecting GPSG-1000 via Antenna Coupler, perform Antenna Coupler
Installation procedure Section 4.1.1. If directly connecting GPSG-1000 to GPS
receiver under test, proceed to step 2.
2. Perform Setup procedure Section 4.1.2.
3. Ensure GPS receiver is in warm start mode i.e. no ephemeris in memory or
receiver has not seen an ephemeris for over 4 Hrs.
4. Select Launch Bar tab to display launch bar. Select SV PRN function key to
display the SV PRN Function Window. The GPS SV’s in view will be displayed in a
table.
5. Turn ON all SV’s by selecting ON/OFF field to ON in each SV line and select
Apply. Select the close icon to close the Function Window.
6. On the Setup Simulation Function Window select PRN Signal drop down menu.
Select VARIABLE, this ensures the relative SV signal levels are set proportional
to the respective pseudo ranges.
7. Select RF Level and set to the receiver manufacturers TTFF RF level.
8. Select Run key to restart simulation and measure the Time to Fix (TTF).