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G3X - GPS Antenna Offset query

BoyRacer

Member
Hi Folks,

For the Garmin G3X, the transponder configuration page provide a “GPS Antenna Offset” entered in feet to show the distance from the GPS antenna to the nose of the aircraft.

If you enter a number will this offset be to the left or right of the aircraft nose/centreline?

e.g. does

A +2 set a GPS antenna offset field apply a 2 feet to the starboard (right) wing
A -2 set a GPA antenna offset field apply a 2 feet to the port (left) wing

Can you even set +/- values for the offset?

The G3X installers manual shows the setting, however does not give any guidance on which direction the offset will be applied.

Keen to hear if anyone has some advice on this one.

Cheers,

Byron.
 
It's a longitudinal offset, not a lateral offset... i.e. how far back from the tip of the spinner the GPS antenna is. I have always assumed the FAA wants to know this so they can get you for crossing a hold-short line.
 
Last edited:
GPS Antenna Offset

Hi Folks,

For the Garmin G3X, the transponder configuration page provide a “GPS Antenna Offset” entered in feet to show the distance from the GPS antenna to the nose of the aircraft.

If you enter a number will this offset be to the left or right of the aircraft nose/centreline?

e.g. does

A +2 set a GPS antenna offset field apply a 2 feet to the starboard (right) wing
A -2 set a GPA antenna offset field apply a 2 feet to the port (left) wing

Can you even set +/- values for the offset?

The G3X installers manual shows the setting, however does not give any guidance on which direction the offset will be applied.

Keen to hear if anyone has some advice on this one.

Cheers,

Byron.

Good Morning Byron,

Check out page 35-157 of the G3X Touch Installation Manual (Rev. AQ), we list all of the transponder configuration settings there with guidance on how to properly set them.

GPS Antenna Offset: Enter the distance from the nose of the aircraft to the GPS antenna used to provide position data to the transponder.

Thanks,

Justin
 
It's a longitudinal offset, not a lateral offset... i.e. how far back from the tip of the spinner the GPS antenna is. I have always assumed the FAA wants to know this so they can get you for crossing a hold-short line.

Thanks! That makes a lot more sense.
 
Good Morning Byron,

Check out page 35-157 of the G3X Touch Installation Manual (Rev. AQ), we list all of the transponder configuration settings there with guidance on how to properly set them.

GPS Antenna Offset: Enter the distance from the nose of the aircraft to the GPS antenna used to provide position data to the transponder.

Thanks,

Justin

Thanks Justin, had incorrectly assumed this setting was a lateral offset, when taxi or lining up on a runway centreline I have noticed the synthetic vision may be a few feet offset from the actual centreline of the plane.
 
Thanks Justin, had incorrectly assumed this setting was a lateral offset, when taxi or lining up on a runway centreline I have noticed the synthetic vision may be a few feet offset from the actual centreline of the plane.

I think somewhere else in the setup there may be a lateral offset input, as well as data such as wingspan. All this high accuracy stuff is needed here in the US for part of the faa’s grand vision - which is to fully automate ground control, at least at major airports. e.g., wingspan is needed to make sure aircraft on parallel taxiways won’t clip wings. Does Australia have a version of adsb?
 
Thanks Justin, had incorrectly assumed this setting was a lateral offset, when taxi or lining up on a runway centreline I have noticed the synthetic vision may be a few feet offset from the actual centreline of the plane.

Between the inherent accuracy limitations of GPS, and the inherent accuracy limitations of databases, I would rate "a few feet" as being pretty good! Regardless, I wouldn't expect the Transponder configuration page to have any effect on the PFD synthetic vision display...
 
I think somewhere else in the setup there may be a lateral offset input, as well as data such as wingspan. All this high accuracy stuff is needed here in the US for part of the faa’s grand vision - which is to fully automate ground control, at least at major airports. e.g., wingspan is needed to make sure aircraft on parallel taxiways won’t clip wings. Does Australia have a version of adsb?

Hi Bob,

We sure do, some requirements for ADSB out in certain airspace. Our federal government has a rebate program running to assist with the cost of installing ADSB equipment, its created quite a rush of installs, too late for me as I already have forked out for my GTX-45R, Recently added a GPS-20 LRU so hence being in the transponder config page to alter settings.

Cheers,

Byron
 
Between the inherent accuracy limitations of GPS, and the inherent accuracy limitations of databases, I would rate "a few feet" as being pretty good! Regardless, I wouldn't expect the Transponder configuration page to have any effect on the PFD synthetic vision display...

Hi Matt,

I recently added a GPS-20 position source to my existing Garmin GTX-45R, it also acts as a GPS source for other LRU in the event of the G3X GPS antenna failing/offline. The GPS-20 provides WAAS compliant position to the GTX-45R so that my SIL meets full ADSB requirements in Australia for controlled airpsace. While running configuring the GTX-45 to take the data from the new GPS-20 I had the query regarding GPS antenna offset. I note the GPS-20 position seems to be more accurate on the synthetic vision than the inbuilt G3X VFR GPS antenna source. Be nice if I can setup the GPS-20 to be the primary position source and the G3X one the backup. Yet to figure out if that is possible or just a configurable setting.

Cheers,

Byron.
 
GPS Data Source

Hi Matt,

I recently added a GPS-20 position source to my existing Garmin GTX-45R, it also acts as a GPS source for other LRU in the event of the G3X GPS antenna failing/offline. The GPS-20 provides WAAS compliant position to the GTX-45R so that my SIL meets full ADSB requirements in Australia for controlled airpsace. While running configuring the GTX-45 to take the data from the new GPS-20 I had the query regarding GPS antenna offset. I note the GPS-20 position seems to be more accurate on the synthetic vision than the inbuilt G3X VFR GPS antenna source. Be nice if I can setup the GPS-20 to be the primary position source and the G3X one the backup. Yet to figure out if that is possible or just a configurable setting.

Cheers,

Byron.

Byron,

If your GPS 20A is connected to the CAN bus, its GPS PVT data gets priority over any other device providing GPS data to the display, so it is already providing GPS data to your G3X Touch display in this case.

Thanks,

Justin
 
Does the offset really matter on small planes? I would think this would be more for airliners

I believe you are correct (this being used for grd ops at large, class B airports) but need to have everything just right if the FAA comes knocking or your ins co is looking to avoid paying a claim.
 
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