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Raymarine forum - [CA11] Axiom Pro speed jumps erratically

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I installed an Axiom Pro 12 last spring. I noticed that the speed (from internal GPS) read fine at 8-9 knots but at 14 knots and above the tenths digits jump erratically. I updated the software at the end of the season to v 3.10.42 and finally last week got to test it. It still has the same problem.
I see that there is now a v 3.11.42. I won't be able to test this version for 4 or 5 months. Is this a known problem? Will this new update solve it?
Kevin
Welcome to the Raymarine Forum Kevin,

The reported symptom may be caused by the effects of sea state on the vessel (i.e. slowing and then speeding up again) or may be indicative insufficient GPS signal strength being received by the system's GPS source. Under flat sea conditions, one may expect that SOG should be reasonably stable. However, as seas build, it would be normal to expect such rapid changes in SOG. With regard to ensuring that the system's GPS receiver, the device which is serving as the system's GPS receiver must have an unobstructed view of the skies overhead. If not, then the addition of an external GPS receiver (ex. Raystar 150 GPS Sensor, etc.) to the system should be considered.
The MFD is on the flybridge with only a bimini as an obstruction. The Axiom Pro is located in the exact same location as my former C90W which didn't have this problem.
Kevin
Chuck,
I experience the exact same condition. I’m running 3.11.42. I’ve had the same issue since May when I first started up after install. I have a video that demonstrates the issue. Calm seas. Axiom Pro 12” with a GA150 antenna. Axiom Pro 9” with the internal antenna turned off. I think the video is attached.

John
All,

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. Accordingly, satisfactory GPS reception of a prior Chartplotter / MFD in an installation location is no guarantee of another Chartplotting / MFD design 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. That said, should the chartplotting product / MFD 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 (typically accompanied by high HDOP ... which is normally 1.0 or less, then it would be recommended that the 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 (typically accompanied by high HDOP ... which is normally 1.0 or less, then it would be recommended that the GPS sensor be sent to Raymarine’s Product Repair Center to be bench checked / serviced.

The symptom shown within the John's video (I believe that this may also be what Kevin is also reporting) is fairly typical and may be improved by increasing the COG/SOG Filter configuration setting. The default value of this setting is MEDIUM, and it would be recommended that it be increased to HIGH.
Chuck,
Changing the filter from medium to high has no effect at all, not that I can observe. What else can be checked?
One of the main issues I have when this is occurs (always above 14.8 Knts) when the autopilot is engaged and I’m trying to judge time to a waypoint. The time try’s to recalculate with changes in speed and the display becomes at times, difficult to read or unusable. Plus I have what amounts to flashing numbers on my instrument display which is frankly, kind of annoying.
I don’t understand why at 14.5 knots, it’s rock steady and at 14.9 it is suddenly Varies so much. I have never had any other Raymarine product or any other GPS do this. I definitely have a hard time accepting it as typical.
If I were to change the antenna selected would you expect the exact same issue at the same speed or would expect different antennas mounted in different locations to product different results? If I can duplicate the same issue with all three antennas would that help identify the cause?

Thanks,
John
John,

When the symptom is observed, what is the reported HDOP value?
Chuck, typically between 1 and 1.2. It was 2.5 with the internal antenna under a hardtop but we added an external antenna and it improved.
John,

Thanks for the additional information. Learning the reported HDOP value when the symptom is observed may be helpful in determining the cause of the symptom. Accordingly, this information will aid in recommending the next course of action.
Chuck,
I launched the boat last week. On the ride to my marina I checked the satellite info.
HDOP 0.6
Accuracy 1.4ft

Speed reading on the Axiom is steady until I reach 14.8 knts at which point it begins to fluctuate from 14.6 - 15.5 or so. As soon as I reduce speed to 14.7 or less it becomes constant or normal again.
HDOP remains constant. Highest reading was 0.8 but it remains steady unlike the speed.

John
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