[CA] [CA11] Axiom 12 GPS speed variations

[Chuck - Raymarine - Moderator]

dtfeld,

Should a GPS receiver be unable acquire sufficient GPS signal strength, or an optimal set of satellites, or be interfered with by RF emissions from within the product or from an external source, GPS reception and accuracy can be adversely affected. Inaccuracies will be manifested as jumping SOG, inaccurate COG, COG values being reported by a vessel is stationary, plotted movement of a stationary vessel (ex. range well in, start a track and leave it on for an hour ... a well functioning system will produce a very small track plot, which may fit entirely beneath the vessel icon). Please click here to view a FAQ providing additional information on this subject.

Chartplotting / MFD products featuring internal GPS receivers differ in their sensitivity, not only due to the quality of the GPS receiver/antenna assemblies used, but also in the RF interference effects of additional circuity (ex. fishfinder, video processing, etc.) housed within the the product. When flush mounted, the mounting surface materials can also have an effect upon reducing GPS signal strength received by the MFD's internal GPS receiver. Satisfactory GPS reception of a prior Chartplotter / MFD in an installation location is no guarantee of another Chartplotting / MFD design being able to satisfactorily receive in that same location. While a hard top would qualify as an obstruction to GPS signal, a fabric bimini would not typically be considered an obstruction ... however, a heavily saturated bimini top may reduce received GPS signal. Satisfactory GPS signal reception is generally determined by verifying that:
- the system's Data Sources feature has been configured to specify that the GPS receiver having the clearest view of the skies overhead has been manually selected as the system's Data Source for GPS, GPS Datum, and Date & Time; and
- the system rapidly acquires and maintains a GPS position FIX; and
- the HDOP reported with the MFD's GPS status dialog is low. This value will typically be 1.0 or less (lower is better) for a GPS receiving device which has been installed in a location affording good reception conditions.

Should there be a concern that the chartplotting product's / MFD's internal GPS receiver is not functioning properly, then it would be recommended that it be temporarily positioned in a location affording it an unobstructed view of the skies overhead and that it be tested in that location to verify its ability to acquire a GPS position FIX, maintain GPS FIX, and report a low HDOP value. Should the MFD's internal GPS sensor pass this test, then it would appear that the MFD's installation location may necessitate that it be interfaced to an external GPS sensor (ex. Raystar 150, Raystar 130, etc.) which in turn will be installed in a location affording it an unobstructed view of the skies overhead. Should the MFD's internal GPS sensor not pass this test, then it then it would be recommended that the Raymarine chartplotting product / MFD be sent to Raymarine’s Product Repair Center to be bench checked / serviced. Similarly, should and external GPS sensor (ex. Raystar 150, Raystar 130, etc.) be the system's GPS data source and be installed in a location affording it an unobstructed view of the skies overhead and be unable to acquire a GPS position FIX, intermittently lose GPS FIX, or produce an inaccurate GPS position FIX, then it would be recommended that the GPS sensor be sent to Raymarine’s Product Repair Center to be bench checked / serviced.

If responding to this post, please respond with the reported HDOP when the vessel is tied dockside and a SOG value greater than 0.0kts being reported by the MFD.