[TG] RS 130 GPS Antenna

[AndrewSimon]

I am having problems with my E120 W. Sometimes it shows the heading perfectly, sometimes it shows the heading up to 120 degrees off course. When shown as the red vector line, sometimes it aligns with green vector line, sometimes it's way off. Replaced fluxgate compass last winter, green vector line and autopilot work perfectly on "auto". When red vector line working correctly can set autopilot on "track" and works perfect. When red vector line shows incorrect heading in relation to actual boat direction, setting autopilot to "track" will turn boat but not follow correct track.

I think problem is in RS 130 antenna. Is there a battery that needs to be replaced in the antenna? Am I on the correct thinking antenna is the problem?

[Tom - Raymarine - Moderator]

Hello Andrew,

The RS130 is what generates your Course Over Ground (COG) and Speed over Ground (SOG) data as well as GPS position, but not heading. COG is the direction you're moving, Heading is the direction you're facing. At higher speeds they'll be very similar, but if you were swinging on a mooring they'd be 90 degrees apart. The red line is heading (purple in newer display software), the green is COG.

A problem with your GPS won't give offset COG, it will generally give no COG data at all if it's got a fault. The fact that the problem affects pilot operation in the way you've described confirms that the erroneous data is the Heading (red), not COG (green.)

If you have a significant discrepancy between COG and heading, the cause will be one of:
- a magnetic influence affecting the fluxgate, e.g. cabling or something ferrous on the other side of the bulkhead from where it's mounted
- normal difference between COG and Heading depending on boat movement, e.g. rapid turns, slow speed, large leeway, tide or current
- a broken winding in the fluxgate (more on this below)
- another heading-related problem with the pilot (depending on which pilot model you have.)

Can you describe how the heading data displays on the pilot screen, when the problem occurs and with the pilot in Standby?
For example, is the heading completely static, does it change with boat turns but very slowly (heavily damped, lags behind), does it drift when on a straight course?

When the problem next occurs, try turning the boat through a slow circle, watching the indicated heading as it goes:
If the heading seems to behave normally through part of the circle and then wrongly through part, this is a strong sign of a broken winding in the fluxgate compass sensor (they're very fine wire windings and can get brittle breaks that make intermittent, end-to-end contacts.)
If, on the other hand, the problem seems to be present all the way round, usually the heading will drift or be laggy - this is a good indication of a Rate Gyro fault.

Finally, there were few very early SPX or S1 model pilots that had component issues on the Course Computer circuit board that could cause a range of intermittent heading issues: if you have one of those models, and the fluxgate and rate gyro don't seem to be the cause, I'd suggest getting the CC looked at by one of our technical service dealers or service centres.

Regards,
Tom