5.4.2.1 GPS-Modes-
Mobile+Mode:!!The!unit!will!continuously!update!its!recorded!position!in!
accordance!to!the!GPS!constellation,!the!internal!GPS!receiver!will!not!perform!any!
position!averaging,!and!will!continuously!compute!both!position!and!time!from!all!
satellites!in!view.!!This!mode!requires!a!minimum!of!five!satellites!to!be!visible!at!all!
times.!
!
This!mode!MUST!be!used!for!portable!applications.!
+
Site+Survey:!!The!GPS!receiver!is!in!the!position!fix!mode!while!it!averages!a!
specified!number!of!sample!positions.!Once!the!averaged!value!is!determined,!the!
receiver!enters!into!position!hold!mode.!
!
Only!use!this!mode!for!FIXED!antenna!locations!such!as!a!rooftop!antenna.!
+
Position+Hold:!!In!this!mode,!the!PTU!will!begin!to!survey!it’s!location!by!collecting!
and!averaging!the!position!that!it!computes!from!the!GPS!satellites.!The!averaged!
position!is!then!stored!into!the!GPS!receiver,!and!the!receiver!transitions!to!a!timing!
mode,!where!the!averaged!position!is!assumed!correct,!and!time!is!only!calculated!
from!all!satellites!in!view.!Erroneous!satellite!tracking!data!can!be!detected!and!
removed!from!the!over-determined!timing!solution!using!the!receiver’s!built!in!
Receiver!Autonomous!Integrity!Monitoring!(RAIM)!function.!In!locations!where!the!
satellite!visibility!is!poor,!the!PTU!can!operate!with!as!few!as!1!satellite!visible!in!
this!mode.!
!
This!mode!gives!the!best!results!with!a!FIXED!antenna.!
5.4.2.2 Cold-Start-GPS-
Forcing!a!gold!start!on!the!GPS!deletes!all!the!current!GPS!almanac!and!real-time!
clock!data!in!the!GPS!receiver,!and!forces!the!GPS!receiver!to!perform!a!sky-search!
to!acquire!GPS!satellite!signals.!!Completion!of!a!cold!start!can!take!up!to!60!minutes.
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