What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

What antennae do I need.

RandyAB

Well Known Member
Building an IFR machine and am planning dual G3X, G5, and GTN750. Aside from the WAAS antenna which I believe is the GA35, what other GPS antennae would be recommended?
 
antenna

I have a dual G3x with xm system and GTN650.

2 - com
1 - vor/loc/gs
1 - GA35 GPS
1 - GA57X XM/GPS
1 - Transponder
2 - GA26C GPS for GDUs
1 - ELT
 
The only thing that could be added to Bob's list is an antenna for a marker beacon, if your audio panel supports one. Roll your own with a 39" wire in a wingtip.
 
Thanks guys. Four GPS units Bob? Aside from the 35 which goes up top, where did you locate the others? I was thinking I would put one on the undersurface of the overhead console. Glare shield for other two?
 
Last edited:
antenna

"...Four GPS units Bob?..."

The GA35 is for the GTN650

The GA57X is for the GDL51R XM/GPS

The GA26C's are for the GDUs. These will go on the glare shield.

I will have to ask Stein about the GA26C for the G5...
 
"...Four GPS units Bob?..."

The GA35 is for the GTN650

The GA57X is for the GDL51R XM/GPS

The GA26C's are for the GDUs. These will go on the glare shield.

I will have to ask Stein about the GA26C for the G5...

You don?t really need the GPS antenna portion of the GA57X. The GDL51R will get the GPS info from the GDU (according to Garmin). I used the GPS portion of the 57X for the G5, and used the two pucks on the glareshield for the GDUs.
 
Thanks guys. Four GPS units Bob? Aside from the 35 which goes up top, where did you locate the others? I was thinking I would put one on the undersurface of the overhead console. Glare shield for other two?

I put the 35 and 57X on top of the cabin, the two pucks on the glareshield. I know... I know... my plane will fall out of the sky because i penetrated the cabin top
 
If you’re not going buying a G3X with the built-in XM receiver, you can use a GA 56, which can be had used for about $50 from eBay. It’s the same as a 57 without XM.

I have a GA 35 for my GTN and then the GA 56 for the G5. The G3X will get GPS signal from either the GTN via GAD 29 or G5 via CAN bus, so you do not need a separate antenna just for that.

BTW, if you use Garmin antennas, you can mount them both 6” apart (CoC) side by side.
 
I have a GA 35 for my GTN and then the GA 56 for the G5. The G3X will get GPS signal from either the GTN via GAD 29 or G5 via CAN bus, so you do not need a separate antenna just for that.

At least one of the G3X screens needs it's own antenna, for dual screens I use one for each.
 
I've got basically the same setup as Bob but I don't have a G5 so I use one GA26 puck on the glareshield for one GDU and the GA57 for the other (I didn't hook up the XM portion as I use FIS-B for Wx).

As far as the Marker beacon, the GTN is a suitable sub so unless you plan on flying a CAT III ILS (joking here for you literal SOBs) I see no benefit even if your audio panel still supports it.
 
Three, four or five GPS antennas? Really?

I am not an expert on Garmin glass, but for IFR I get by just fine with one SkyView GPS antenna and one GTN-650 GPS antenna. On the RV-10 both were mounted on the glare shield. Considering the temperamental aspects of the GTN-650 I now recommend mounting that GPS antenna on the cabin top. On the RV-8A and RV-8 the SkyView is on the glare shield and the GTN-650 is on the top of the fuselage just behind the passenger?s head.
The rest of the antennas are basic:
- Transponder
- ADS-B
- Two comm
- One wingtip VOR/LOC/GS

On the RV-10 I did add a piece of wire strung out under the engine (inside the cowl) for the audio panel Marker Beacon antenna. It works just fine as it has gone off flying at altitude over major airports. Other than that it has never been used an any real or practice approach. I recommend not having a Marker Beacon receiver.

Carl
 
Yes

Yes Carl, those antennas were what was recommended...

I am also not a Garmin expert so I went with the expert’s recommendations...0
 
Three, four or five GPS antennas? Really?

I am not an expert on Garmin glass, but for IFR I get by just fine with one SkyView GPS antenna and one GTN-650 GPS antenna. On the RV-10 both were mounted on the glare shield. Considering the temperamental aspects of the GTN-650 I now recommend mounting that GPS antenna on the cabin top. On the RV-8A and RV-8 the SkyView is on the glare shield and the GTN-650 is on the top of the fuselage just behind the passenger?s head.
The rest of the antennas are basic:
- Transponder
- ADS-B
- Two comm
- One wingtip VOR/LOC/GS

On the RV-10 I did add a piece of wire strung out under the engine (inside the cowl) for the audio panel Marker Beacon antenna. It works just fine as it has gone off flying at altitude over major airports. Other than that it has never been used an any real or practice approach. I recommend not having a Marker Beacon receiver.

Carl

The only IFR part of a GARMIN panel is either a GNS or GTN navigator -- so one antenna there. The other GPS antennas are VFR -- one for each screen as each screen has it's own built-in VFR GPS. So really there's no difference than what you have with your system.
 
The only IFR part of a GARMIN panel is either a GNS or GTN navigator -- so one antenna there. The other GPS antennas are VFR -- one for each screen as each screen has it's own built-in VFR GPS. So really there's no difference than what you have with your system.

So a dual Garmin G3X install needs a GPS antenna for each display? I would not have guessed.

Each SkyView display uses the same GPS antenna via serial ports. The functioning of one display does not affect the other in this aspect.

Carl
 
So a dual Garmin G3X install needs a GPS antenna for each display? I would not have guessed.

Each SkyView display uses the same GPS antenna via serial ports. The functioning of one display does not affect the other in this aspect.

Carl

No -- only one GPS antenna is required just like with the Dynon. The display with the antenna will share its GPS data with multiple screens. But as each screen has its own integrated GPS most of us add the extra antenna(s) simply to add system redundancy in case of a screen failure.
 
I have Dual G3X, G5 and a GTN 650. I have the GA-35 for the GTN and two GA56's, one for the G3X and one for the G5.

All seem to work great!
 
No -- only one GPS antenna is required just like with the Dynon. The display with the antenna will share its GPS data with multiple screens. But as each screen has its own integrated GPS most of us add the extra antenna(s) simply to add system redundancy in case of a screen failure.

Ok - now I get it. The G3X has an internal GPS receive that needs an antenna for each display. The SkyView uses an integrated GPS receiver/antenna so the one unit can independently feed multiple displays.

Carl
 
For a system that is as well integrated as Garmin I'm surprised that each unit would require it's own antenna and not simply get the data from the other units on the bus. Two units seems 100% reasonable, the others appear to me to be a bit overkill. I will put the backup 57x in the overhead console with the 35 on top for now and worry about any additional pucks on the glare shield later when I cross that bridge. For now I'm just having to decide on what wires to run up top before everything gets more difficult access.
 
Last edited:
For a system that is as well integrated as Garmin I'm surprised that each unit would require it's own antenna and not simply get the data from the other units on the bus.

From the G3X installation manual:

Unless a GPS 20A is used for GPS position, a minimum of one GPS antenna is required
for installations using more than one GDU 4XX unit, as the GDU 4XX will ?share? the
GPS information with all GDU 46X units. Additional GPS antennas may be used for
redundancy, but are not required.​
 
At least one of the G3X screens needs it's own antenna, for dual screens I use one for each.

No, they work just fine with input from either external source and sharing that data, using the GTN. And having the G5 with it's own valid antenna, it can share GPS data with the G3X, much like a GPS 20 will as well. And since the OP stated they have a GTN, no additional antenna is required for the G3X. Lastly, they do have internal GPS as well, but it is not shared.

If you want your G3X to have it's own antenna, you can do that, but they don't need it. I can attest to this in practice. What's more, the GDU's will only use one GPS signal source at a time, so if you have the GTN configured to provide that signal as an external source, then the internal source (which includes attaching a GA 56 directly to the GDU) won't even be used, except as a backup you could select if the GTN failed. But, you have the G5, right? It can provide that GPS signal as well when configured with it's own antenna.

I see a GA56 for the G5 and a GA 35 for the GTN and that's redundancy and all you really need for GPS related antennas.
 
Last edited:
No, they work just fine with input from either external source and sharing that data, using the GTN. And having the G5 with it's own valid antenna, it can share GPS data with the G3X, much like a GPS 20 will as well. And since the OP stated they have a GTN, no additional antenna is required for the G3X. Lastly, they do have internal GPS as well, but it is not shared.

If you want your G3X to have it's own antenna, you can do that, but they don't need it. I can attest to this in practice. What's more, the GDU's will only use one GPS signal source at a time, so if you have the GTN configured to provide that signal as an external source, then the internal source (which includes attaching a GA 56 directly to the GDU) won't even be used, except as a backup you could select if the GTN failed. But, you have the G5, right? It can provide that GPS signal as well when configured with it's own antenna.

I see a GA56 for the G5 and a GA 35 for the GTN and that's redundancy and all you really need for GPS related antennas.

Maybe the G3Xpert will jump in here, the below is from their manual which I tend to believe:

7 GDU 45X (DISPLAY UNIT) INSTALLATION

NOTE
"GPS data is used for ADAHRS sensor drift correction, so at least one source of GPS data is required. This requirement can be met by installing a GPS 20A, or by connecting a GPS antenna to at least one GDU GPS receiver. In a system with multiple GDU displays, additional GPS antennas may be connected to the other displays for redundancy, if desired."
 
Last edited:
Maybe the G3Xpert will jump in here, the below is from their manual which I tend to believe:

7 GDU 45X (DISPLAY UNIT) INSTALLATION

NOTE
"GPS data is used for ADAHRS sensor drift correction, so at least one source of GPS data is required. This requirement can be met by installing a GPS 20A, or by connecting a GPS antenna to at least one GDU GPS receiver. In a system with multiple GDU displays, additional GPS antennas may be connected to the other displays for redundancy, if desired."

Exactly; if you don't have an external GPS source, then you need to connect an antenna directly to one of GDU's, but the OP has an external navigation source, along with a G5 to provide a redundant ADAHRS and GPS source. The paragraph below is from the G5 installation manual for non-certified aircraft:

"1.2 G5 Overview
The G5 is an electronic instrument display capable of operating as a standalone flight display or a fully integrated backup instrument for G3X systems. It features a bright, sunlight readable, 3.5-inch color display which is sized to fit in a standard 3-1/8-inch instrument cutout. With integrated attitude/ air data sensors and GPS, the G5 replaces traditional electromechanical standby instruments by combining essential information into one easy-to-read display. The G5 seamlessly integrates with other G5 units in the same aircraft and with G3X systems via the CAN network. When installed as part of a G3X system, the G5 provides a redundant source of attitude and air data to the G3X displays, and additionally provides backup autopilot control allowing coupled GPS approaches to be flown or continued in the event that the primary flight display is unavailable. When installed as a standalone system, the G5 can also perform the autopilot function. In the case of aircraft power loss, the optional battery backup sustains the G5 flight display with up to 4 hours of emergency power."

Walt, the GDU's only use the the individually attached GPS antenna for ADAHRS data while using navigation data from an external source, such as a GTN. But this data is also being provided on CAN bus from the G5, so the additional antenna connected to the GDU is simply more redundancy. I'm not saying don't do it - for that matter you can attach an antenna to both PFD, MFD and even a third GDU, if desired - I'm simply saying it's not needed and the OP's question is "What antennas do I need?"

I have done this setup and it works well.
 
Last edited:
"...Four GPS units Bob?..."

The GA35 is for the GTN650

The GA57X is for the GDL51R XM/GPS

The GA26C's are for the GDUs. These will go on the glare shield.

I will have to ask Stein about the GA26C for the G5...

I'm not Stein, nor G3Xpert, so my advice is probably only worth what you're paying for it.... however, I can confirm the G5 will use a GA26C antenna. Below is an excerpt from the G5 installation manual:

Table 4-2 Supported Garmin Antennas
Model
Part Number
Install Manual
Mounting Configuration
GA 26C (GPS)
011-00149-04
190-00082-00
Flange, Magnetic, or Suction Cup Mounts (in-cabin)
GA 35 (GPS/WAAS)
013-00235-0X
190-00848-00
Thru-Mount (tear drop form factor)
GA 36 (GPS/WAAS)
013-00244-0X
190-00848-00
Thru-Mount (ARINC 743 form factor)
GA 56 (GPS)
011-00134-00
190-00094-00
Stud Mount (tear drop form factor)
GA 57X (GPS/XM)
011-01032-10
190-00522-02
Thru-Mount (ARINC 743 form factor)
 
Building an IFR machine and am planning dual G3X, G5, and GTN750. Aside from the WAAS antenna which I believe is the GA35, what other GPS antennae would be recommended?
Hello Randy,

We recommend you install a GPS for antenna for the GDU 4XX PFD (e.g. GA 26C or GA 56), the G5 (e.g. GA 26C or GA 56), and the GTN 750 (e.g. GA 35/36).

As explained in the G3X installation manual, at least one of the GDU 4XX displays must have an antenna connected unless you have a GPS 20A, but even in that case, we still recommend an antenna on the PFD display for backup to the GPS 20A.

I like to tell customers that the most important GPS in the aircraft is not the GTN, but rather the high performance WAAS GPS receiver built into each GDU 4XX display because it provides GPS acceleration data used by the GSU 25 ADAHRS to correct for small drifting errors in the solid state attitude sensors.

The GSU 25 ADAHRS can use air data and magnetometer data to correct for sensor drift in the absence of GPS data, but the highest level of performance and accuracy is only obtained when GPS data is available and used for aiding.

The GPS data from the GTN and G5 can be used as backup navigation data for the GDU displays, but it cannot currently be used to aid the GSU 25 ADAHRS.

Interestingly, there are 2 additional sources of GPS data (besides the GDU and GPS 20A) which provide data that can be used to aid the GSU 25, and that is a GTX 345 w/GPS and a GNX 375. Just like when using a GPS 20A, we still recommend that at least the PFD have its own antenna.

Note also that the G5 backup instrument can use either its internal GPS receiver or the MapMX data it is receiving directly from the GTN for attitude sensor aiding, but in some kind of aircraft power emergency, where you might be left with only the G5 operating on its internal backup battery, you will be glad that you connected an antenna to the G5. Like the GSU 25, the G5 can use alternate sources of aiding, but GPS aiding provides the highest accuracy.

Let us know if you have additional questions.

Thanks,
Steve
 
Last edited:
Walt, the GDU's only use the the individually attached GPS antenna for ADAHRS data while using navigation data from an external source, such as a GTN. But this data is also being provided on CAN bus from the G5, so the additional antenna connected to the GDU is simply more redundancy. I'm not saying don't do it - for that matter you can attach an antenna to both PFD, MFD and even a third GDU, if desired - I'm simply saying it's not needed and the OP's question is "What antennas do I need?"

I have done this setup and it works well.

Hello Randy,

As explained in the G3X installation manual, at least one of the GDU 4XX displays must have an antenna connected unless you have a GPS 20A, but even in that case, we still recommend an antenna on the PFD display for backup to the GPS 20A.

I like to tell customers that the most important GPS in the aircraft is not the GTN, but rather the high performance WAAS GPS receiver built into each GDU 4XX display because it provides GPS acceleration data used by the GSU 25 ADAHRS to correct for small drifting errors in the solid state attitude sensors.

The GSU 25 ADAHRS can use air data and magnetometer data to correct for sensor drift in the absence of GPS data, but the highest level of performance and accuracy is only obtained when GPS data is available and used for aiding.

The GPS data from the GTN and G5 can be used as backup navigation data for the GDU displays, but it cannot currently be used to aid the GSU 25 ADAHRS.

Thanks,
Steve

Thanks for jumping in here Steve!

Ron, perhaps the above will change your mind? Steve is the brains behind the G3X and I take his word as gospel. I guess we could argue the semantics of "required" vs "recommended" but when the manufacturer "recommends" something they generally have a good reason for it.
 
Thanks for jumping in here Steve!

Ron, perhaps the above will change your mind? Steve is the brains behind the G3X and I take his word as gospel. I guess we could argue the semantics of "required" vs "recommended" but when the manufacturer "recommends" something they generally have a good reason for it.

Walt, I don't see any contrary information here or anything to be changed from what has been said, although it's nice to hear that the GNX 375 can provide that data to the GSU 25, as that's what I'm planning for my RV10. Again, it's all about redundancy and want vs need. I can tell you that the system works well using the ADAHRS data from the G5; it's going to be hard to argue against my own experience. My point is defining minimum, or functional, versus redundancies.

Fortunately, Garmin has a very well integrated environment that allows you to expand to just about any level of redundancy you desire, but the minimum required is just that. Adding a GPS antenna to one or both of the GDU's and then adding a G5 does give you multiple redundant ADAHRS capability - and that's something I would do before adding a second GSU 25 - but you could do that too if even more redundancy is your goal.

Going hard IFR? Add more. Day VFR? The minimum will be just fine...I think it's important to understand the difference.
 
Last edited:
Ron, The only reason I continue this silly "debate" is I think it's important that folks follow the manufacturers recommendations to achieve the level of performance designed into the system, and I wish you would stop saying that it ok to not install the recommended GPS antennas/sources because it works for you.

I think you are somehow reading into Steve's comments what you want to hear.
It's not about redundancy.

Please read Steve's comment below again:

"I like to tell customers that the most important GPS in the aircraft is not the GTN, but rather the high performance WAAS GPS receiver built into each GDU 4XX display because it provides GPS acceleration data used by the GSU 25 ADAHRS to correct for small drifting errors in the solid state attitude sensors.

The GSU 25 ADAHRS can use air data and magnetometer data to correct for sensor drift in the absence of GPS data, but the highest level of performance and accuracy is only obtained when GPS data is available and used for aiding."

Steve has already included the GPS sources that will support the GSU25 ADAHRS aiding so no need to repeat that info again.
 
Last edited:
Ron, The only reason I continue this silly "debate" is I think it's important that folks follow the manufacturers recommendations to achieve the level of performance designed into the system, and I wish you would stop saying that it ok to not install the recommended GPS antennas/sources because it works for you.

I think you are just reading into Steve's comments what you want to hear.
Watch my lips: It's not about redundancy.

Please read Steve's comment below again:

"I like to tell customers that the most important GPS in the aircraft is not the GTN, but rather the high performance WAAS GPS receiver built into each GDU 4XX display because it provides GPS acceleration data used by the GSU 25 ADAHRS to correct for small drifting errors in the solid state attitude sensors.

The GSU 25 ADAHRS can use air data and magnetometer data to correct for sensor drift in the absence of GPS data, but the highest level of performance and accuracy is only obtained when GPS data is available and used for aiding."

Steve has already included the GPS sources that will support the GSU25 ADAHRS aiding so no need to repeat that info again.

Ok, Walt, I'll continue, although I don't actually consider it a debate... first, re-read my previous posts; I haven't told anyone not to use an antenna or not perform an installation; in fact, everything I've said came from Garmin instructions, so I'm not avoiding those either - you may use all of the antennas you want; I'm simply pointing out options.

You may have missed my point that you can get ADAHRS data on the G3X from the G5. You don't even need to have a GSU 25 for this to occur. And seeing you highlighted "It's not about redundancy", not including additional antennas or the GSU 25 saves cost and effort. For that matter, you don't even need the GDU's if you have the G5, saving even more money and installation effort.

Now, does it make sense to install a GPS antenna if you're installing a PFD? Maybe. How about on the MFD too? Maybe as well. It makes sense to come in out of the rain when it's thundering out, but there are folks that don't. It's their choice, and level of risk they perceive as ok.

Steve pointed out, there are other options for GPS sources to the GDU, so you really don't need to have the extra antenna - unless redundancy is actually a concern for you.

Do you want an antenna on all your GDU's? Maybe. The OP could have 4 GPS antennas for their installation described if they wanted them, but they only need two to make the "system" work - and that was the actual question.
 
GDL-82 VS. GPS 20A

We recommend you install a GPS for antenna for......the G5 (e.g. GA 26C or GA 56).....

As explained in the G3X installation manual, at least one of the GDU 4XX displays must have an antenna connected unless you have a GPS 20A, but even in that case, we still recommend an antenna on the PFD display for backup to the GPS 20A........

Note also that the G5 backup instrument can use either its internal GPS receiver or the MapMX data it is receiving directly from the GTN for attitude sensor aiding, but in some kind of aircraft power emergency, where you might be left with only the G5 operating on its internal backup battery, you will be glad that you connected an antenna to the G5. Like the GSU 25, the G5 can use alternate sources of aiding, but GPS aiding provides the highest accuracy.....

Thanks,
Steve

Steve,

You mentioned the the GPS 20A as playing an important part in redundancy. Will the WAAS antenna that’s part of the GDL-82 play the same redundancy roll when being installed along with a stand-alone G-5/660 combo?
 
Steve,

You mentioned the the GPS 20A as playing an important part in redundancy. Will the WAAS antenna that?s part of the GDL-82 play the same redundancy roll when being installed along with a stand-alone G-5/660 combo?
Hello Mark,

The GDL 82 has a very nice WAAS GPS receiver with the same specs as the GPS 20A, but it doesn't share any GPS data with your G5/Aera 660 system (or any system for that matter).

Thanks,
Steve
 
Hello Mark,

The GDL 82 has a very nice WAAS GPS receiver with the same specs as the GPS 20A, but it doesn't share any GPS data with your G5/Aera 660 system (or any system for that matter).

Thanks,
Steve

Thanks for the reply Steve. Is there anything that you would recommend (antenna wise) to boost the robustness/reliability/redundancy of a stand alone G-5/660 setup?

Thanks again.
 
Thanks for the reply Steve. Is there anything that you would recommend (antenna wise) to boost the robustness/reliability/redundancy of a stand alone G-5/660 setup?

Thanks again.
Hello Mark,

Each G5 unit has a built-in GPS antenna, but it doesn't receive well in some panels, which is why we recommend an external antenna (a glare shield antenna is normally fine) on at least the G5 PFD.

If you don't see lots of green bars and a green check mark on the G5 GPS page (all the time), that means that your receiver needs a better antenna.

The green check mark means that the GPS signal is of sufficient quality for the G5 to use the GPS data for attitude sensor error correction.

lz0l5cVUWPW66mSCcvkXDZZc6iebg8Y-Pjfc0ayxnm1HzHbVvdLVsgPW-QZjqexnZA_bUKnClnqoFtLvSecSlRJCwJnDmy8MeLfHEjgOYnOZa1VvvsTXmIuO07gbB_UPzeYYuaDG7B8zy4kcNx0UAJUwctW922SUlG2wML7C84AF2pYduPWhWRdjAIT6DTECKXS6QGnSmgA4ZETeqDa1h1QO7JNq8bxWqZSCmctbZR8k0N39AjV0gV6oe9E20P_JDlXKJvLDdfbhpUrvn5s-aBzzMhsMlG4XP6WRcCD3wsRitYOoz_-CzencMABP1FnRIshrFD1xoD7wPivV7pph1qQV9_DkKScWGszrEJsza-RSXkQxPizX0PdnZ9VIEjqGE-Ua4fivnYzGiTxAi_-sjqRWB-zty7bmZlbqEaQltvTSohPobTS6E5Hq_UYvWwlW5qQ4RT0YgpuAv4zv9jUDMTRau9hjm9NHAHx76a1acJPkHFf3sgB2BOzV51Za36n5Belt1aPEy0u08dw_8veYPOrge6Rut06BwYaSELWKKSshevZ1Q8CB5LgpidvSaa1cLf8V7sFmB3WqbcxT0YAZNCIKULwINgMaUs3L1gB1HJmrFqkNqY0r2G5q01OUTYjtTVHFHYqxoKRChwXnSjKTMkRI4P5aQqfeqb9A1aa3JzywpahvAawIxA=w320-h240-no


Thanks,
Steve
 
Hello Randy,

We recommend you install a GPS for antenna for the GDU 4XX PFD (e.g. GA 26C or GA 56), the G5 (e.g. GA 26C or GA 56), and the GTN 750 (e.g. GA 35/36).

As explained in the G3X installation manual, at least one of the GDU 4XX displays must have an antenna connected unless you have a GPS 20A, but even in that case, we still recommend an antenna on the PFD display for backup to the GPS 20A.

I like to tell customers that the most important GPS in the aircraft is not the GTN, but rather the high performance WAAS GPS receiver built into each GDU 4XX display because it provides GPS acceleration data used by the GSU 25 ADAHRS to correct for small drifting errors in the solid state attitude sensors.

The GSU 25 ADAHRS can use air data and magnetometer data to correct for sensor drift in the absence of GPS data, but the highest level of performance and accuracy is only obtained when GPS data is available and used for aiding.

The GPS data from the GTN and G5 can be used as backup navigation data for the GDU displays, but it cannot currently be used to aid the GSU 25 ADAHRS.

Interestingly, there are 2 additional sources of GPS data (besides the GDU and GPS 20A) which provide data that can be used to aid the GSU 25, and that is a GTX 345 w/GPS and a GNX 375. Just like when using a GPS 20A, we still recommend that at least the PFD have its own antenna.

Note also that the G5 backup instrument can use either its internal GPS receiver or the MapMX data it is receiving directly from the GTN for attitude sensor aiding, but in some kind of aircraft power emergency, where you might be left with only the G5 operating on its internal backup battery, you will be glad that you connected an antenna to the G5. Like the GSU 25, the G5 can use alternate sources of aiding, but GPS aiding provides the highest accuracy.

Let us know if you have additional questions.

Thanks,
Steve

I have a GPS 20A with its own antenna, and have the MFD connected to a GA56 on the glare shield. It seems from this post that the antenna should be connected to the PFD instead - is this correct? Have I been missing the GPS correction data?

Also, I plan to add a GPS 175 and remove the GPS 20A as the ADS-B position source. Is this a valid config?
 
Hello Randy,

We recommend you install a GPS for antenna for the GDU 4XX PFD (e.g. GA 26C or GA 56), the G5 (e.g. GA 26C or GA 56), and the GTN 750 (e.g. GA 35/36).

As explained in the G3X installation manual, at least one of the GDU 4XX displays must have an antenna connected unless you have a GPS 20A, but even in that case, we still recommend an antenna on the PFD display for backup to the GPS 20A.

I like to tell customers that the most important GPS in the aircraft is not the GTN, but rather the high performance WAAS GPS receiver built into each GDU 4XX display because it provides GPS acceleration data used by the GSU 25 ADAHRS to correct for small drifting errors in the solid state attitude sensors.

The GSU 25 ADAHRS can use air data and magnetometer data to correct for sensor drift in the absence of GPS data, but the highest level of performance and accuracy is only obtained when GPS data is available and used for aiding.

The GPS data from the GTN and G5 can be used as backup navigation data for the GDU displays, but it cannot currently be used to aid the GSU 25 ADAHRS.

Interestingly, there are 2 additional sources of GPS data (besides the GDU and GPS 20A) which provide data that can be used to aid the GSU 25, and that is a GTX 345 w/GPS and a GNX 375. Just like when using a GPS 20A, we still recommend that at least the PFD have its own antenna.

Note also that the G5 backup instrument can use either its internal GPS receiver or the MapMX data it is receiving directly from the GTN for attitude sensor aiding, but in some kind of aircraft power emergency, where you might be left with only the G5 operating on its internal backup battery, you will be glad that you connected an antenna to the G5. Like the GSU 25, the G5 can use alternate sources of aiding, but GPS aiding provides the highest accuracy.

Let us know if you have additional questions.

Thanks,
Steve

Thanks Steve. So for clarity, I will install the GA 35 for the GTN 750, the GA 57X for the G3X PFD, and a GA 26 for each of the G5 and the secondary G3X. Does this sound like a good arrangement?
 
Back
Top