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natedawgsem

What is the preferred external GPS antenna model number for the Axion Pro's? The GA150 or the RS150?

***Tom - Raymarine - Moderator***

Hello natedawgsem,

There's not a lot of difference in performance between them. Having the GPS receiver electronics away from the display is a bit of a lower-noise environment which will probably give slightly higher (even higher) fix accuracy than using GA150 (when you use a GA150 you're attaching a passive antenna, effectively an aerial, to the internal receiver in the display), and the RS150's STNG cable is probably easier to run through the boat (don't ever cut and re-terminate the GA150's cable, and its connector is bigger), but the RS150 is more expensive.

A 3rd alternative for you: the AR200 (http://www.raymarine.com.au/gps/ar200/) combines RS150-quality GPS with the heading sensor from an EV autopilot, also enables ClearCruise Augmented Reality overlay on connected CAM210, CAM220 and M232 video cameras (http://www.raymarine.com.au/clearcruise/), and is not that big a step up from RS150. If you'd thought of adding a visible-light or thermal camera, or don't have heading data from an autopilot, then the AR200 is well worth looking at.

Regards,
Tom

carlmk

From my experience an external GPS antenna is just much better than the built-in ones found in Axiom 9 and Axiom Pro 12 that are installed. I tried moving the external one to the worst places in my boat and it never lost capture. The Axiom internal attennae lost capture no matter wher I placed them.

***Tom - Raymarine - Moderator*** · 06-04-19, 09:18 PM

Hello carlmk,

Internal antennas, since they're surrounded by other electronics, operate in a higher-noise environment, and have to pick up their signal through the LCD and housing etc.. Axiom standard displays in particular have their antenna set a bit further back in the case compared to Axiom Pro and need a fairly good view of the sky.

We've also seen that - at least here in Australia and New Zealand - you can get a much less reliable fix when Differential mode is enabled, as is the default. This is because when the system uses Differential mode, it prefers to only use satellites for which the differential corrections are available, which means only the satellites which are visible from both your location and where the differential service is aimed at. In Australia/NZ, where there is no local SBAS service, we always recommend turning Differential off.

If you've got an Axiom Pro with recent software and a half-reasonable view of the sky and it's not getting a rock-solid GPS signal with at least half-metre accuracy (we typically get 0.6-0.8m accuracy with Differential off) then either there's another GPS in your system taking priority, or you have lots of RF interference (an increasingly common problem) or you have a fault with the Pro. I am completely confident in Pro's internal GPS. As I say, standard Axiom doesn't have it quite so easy because of where we've had to place the antenna, but they still work fine as long as they have a good sky view.

To anyone else reading this: if you have GPS problems with an Axiom or Pro, what we ask for here in Australia in order to understand the cause is:

clear, wide-angle photos of the mounting location (in relation to the rest of the boat and what's above and around it) of the MFD
photos or better video showing the contents of Home > GPS (top-left) > Satellites
A recording of the NMEA2000 data in the system, at the time when the poor-GPS problems are occurring (http://forum.raymarine.com/showthread.php?tid=6849)

If you can post this back here, we can usually see why the GPS isn't performing as we know they're capable of doing.

Tom

natedawgsem

Why is it not recommended to re-terminate the TNC connector on the GA150? If ou have the correct TNC connector and crimp tool there shouldn't be an issue. Does the length of the cable play a role in the antennas effectiveness? Once connected to the unit, will it show the device under the "GPS" network devices menu?

***Tom - Raymarine - Moderator*** · 06-27-19, 01:45 AM

Hello natedawgsem,

Quote:Why is it not recommended to re-terminate the TNC connector on the GA150? If ou have the correct TNC connector and crimp tool there shouldn't be an issue. Does the length of the cable play a role in the antennas effectiveness?

That depends on the quality of your termination. GPS signals are low-power (see where GPS sits in the scale at https://en.wikipedia.org/wiki/Orders_of_...de_(power)) and it takes very little to either alter the impedance mismatch in the cable which is required to transfer that signal back to the GPS receiver in the display, or to mask that signal in noise picked up on the cable. A connection that looks fine by eye and measures fine for DC resistance on a multimeter might be anything but fine to a low-power, 1.5GHz RF signal.

My general answer to this sort of thing is that if you're an RF tech then you know the answers better than I do, and if you're not then you shouldn't be doing it. I wouldn't. And there's no warranty on the antenna or technical support if you have GPS problems after doing so.

Quote:Once connected to the unit, will it show the device under the "GPS" network devices menu?

This is a common question. No, the GA150 is a passive antenna with no digital communications with the display and it will not be listed as a device in any diagnostic. The only way to tell it's there is the drop in GPS signal strengths in the Satellite Status page (top-left on the Home screen in LH3, Satellites) when you unplug it.

Regards,
Tom