Viavi 87339, Руководство по эксплуатации

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Testing
4 -13
4.1.7.A Acquisition (cold start)
Under this condition the receiver does not have any current Almanac or Ephemeris data
and has no memory of previous location. Firstly, at least one GPS frame must be
downloaded from each of the SV’s in view however, as the receiver does not even know it
approximate location and hence what SV’s may be in view, this requires all SV PRN
codes to be searched, over 5000 Hz Doppler frequency shift. Most modern receivers
achieve a position fix from a cold start condition in 30 to 60 seconds. In older receivers
this process may take several minutes.
Perform the following steps for Acquisition (cold 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 cold start mode i.e. no almanac or ephemeris in
memory.
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 (Fig 4-4).
5. Turn ON all SV’s by selecting ON/OFF field to ON in each SV line and then 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).