7-2 Activating the GPS Feature GPS Receiver, Option 31
7-2 PN: 10580-00305 Rev. L MS20xxC UG
4. When the GPS receiver is tracking at least four satellites, the GPS icon changes to
green. Latitude and longitude information is displayed in the title bar at the top of the
display. Acquiring satellites may take as long as three minutes.
5. Press the GPS Info submenu key to display the following information:
• Tracked satellites
• Latitude and longitude
• Altitude
• UTC timing information
• Fix available
• Almanac complete
• Antenna and receiver status
• GPS antenna voltage and current
Refer to “GPS Menu” on page 7-4 for details on the above GPS Info items.
After GPS location fix is attained, the internal reference oscillator begins to correct its
frequency to match the GPS standard. After the internal frequency is adjusted to match the
GPS standard, the status is indicated by “GPS High Accuracy” showing in the Status menu,
which is displayed on the left side of the measurement display. When the GPS feature is not
enabled, the reference source displays either “Internal Standard Accuracy” or a user-selected
external reference frequency in the Status menu.
Within three minutes of satellite acquisition, the reference oscillator will have an accuracy of
better than 25 ppb (parts per billion). The OCXO internal standard accuracy is ±0.3 PPM.
The correction factor applied to the internal OCXO allows the instrument to maintain GPS
frequency accuracy for three days at better than 50 ppb, even when the instrument is
obstructed from receiving signals from the GPS satellites.
In order to acquire data from the GPS satellites, you must have line-of-sight to the satellites,
or the antenna must be placed outside with no obstructions.
If no GPS is connected for at least three days, the Frequency Reference annotation reads Int
Std Accy.
When GPS is connected, with a fix, and the tuning process has completed (which may take a
few minutes), the Frequency Reference annotation shows GPS Hi Accy. If GPS is
subsequently lost (for example, GPS is turned off, disconnected, or there is no signal due to
physical obstruction), the instrument goes back to Int Hi Accy after a few moments. If GPS
remains disconnected for three consecutive days, whether the instrument is on or off, the
instrument reverts to Int Std Accy.
Figure 7-2. GPS Icon, Green
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