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Thread: Garmin G3x Wiring Questions

  1. #11
    Senior Member efwd's Avatar
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    Default Re: Garmin G3x Wiring Questions

    Garmin Support 866=739-5687
    Eddie Forward
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    SS7, 912iS, Garmin G3X

  2. #12
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    Default Re: Garmin G3x Wiring Questions

    Next question. Seems like I read somewhere in the 900 page manual, does the G3x need permanent 12v power?
    Last edited by Shadowrider; 07-22-2019 at 03:46 PM.
    Dustin Dickerson

    Building 7ss STI x 2
    Oratex
    29" shock monster
    EP912STI 155hp
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  3. #13
    Senior Member PapuaPilot's Avatar
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    Default Re: Garmin G3x Wiring Questions

    No, it doesn't need any kind of keep alive power.

    Most of the LRUs have 2 pins so you can power it from 2 sources if you desire.
    Phil Nelson
    A&P-IA, Maintenance Instructor
    KF 5, Continental IO-240
    Flying

  4. #14
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    Default Re: Garmin G3x Wiring Questions

    Quote Originally Posted by PapuaPilot View Post
    No, it doesn't need any kind of keep alive power.

    Most of the LRUs have 2 pins so you can power it from 2 sources if you desire.
    Thanks! My "reading" is not so bad.........my "recall" not so good
    Dustin Dickerson

    Building 7ss STI x 2
    Oratex
    29" shock monster
    EP912STI 155hp
    Garmin
    N33TF
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  5. #15
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    Default Re: Garmin G3x Wiring Questions

    Who knows the gtx45R? From what I am gathering, RS-232 (1) is used for GSU-25(adahars) RS-232 (2) is for the GDU 4xx (G3X touch screen). Do I just use RS-232 (3) for the GPS 20 input?

    I guess what I am asking is I am running the GPS-20, which is providing wass gps signal to the transponder. Isn't the transponder going to use waas gps position and altitude from the transponder? So do I still provide info from the GSU-25, which is providing altitude via static pressure?
    Dustin Dickerson

    Building 7ss STI x 2
    Oratex
    29" shock monster
    EP912STI 155hp
    Garmin
    N33TF
    N53TF

  6. #16
    Senior Member PapuaPilot's Avatar
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    Default Re: Garmin G3x Wiring Questions

    I'm not totally sure I understand all of your questions, but this may help.

    The GPS-20A is your WAAS GPS source required for ADSB-out position and possibly IFR navigation. It's not the altitude source for the transponder as GPS altitude is not overly accurate. The altitude source for the transponder/ADSB and the display(s) (GDUs) comes from the ADAHRS (GSU-25). The GSU-25 provides pressure altitude, which is corrected using the altimeter setting and is very accurate.

    I'm not sure how all of these hook up and communicate with each other with the GTX-45R. I have a different transponder. My GPS-20A connects directly to the transponder using a RS-232 channel and sends its data on the CAN bus too. The CAN bus connects to both the GSU-25 and GDU-465. Therefore using both the CAN bus and RS-232 the WAAS GPS position is provided to the entire G3X system.

    You are going to need to look carefully in the installation manual chapters 26 and 27 to find the answer to this.
    Phil Nelson
    A&P-IA, Maintenance Instructor
    KF 5, Continental IO-240
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  7. #17
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    Default Re: Garmin G3x Wiring Questions

    Quote Originally Posted by PapuaPilot View Post
    I'm not totally sure I understand all of your questions, but this may help.

    The GPS-20A is your WAAS GPS source required for ADSB-out position and possibly IFR navigation. It's not the altitude source for the transponder as GPS altitude is not overly accurate. The altitude source for the transponder/ADSB and the display(s) (GDUs) comes from the ADAHRS (GSU-25). The GSU-25 provides pressure altitude, which is corrected using the altimeter setting and is very accurate.

    I'm not sure how all of these hook up and communicate with each other with the GTX-45R. I have a different transponder. My GPS-20A connects directly to the transponder using a RS-232 channel and sends its data on the CAN bus too. The CAN bus connects to both the GSU-25 and GDU-465. Therefore using both the CAN bus and RS-232 the WAAS GPS position is provided to the entire G3X system.

    You are going to need to look carefully in the installation manual chapters 26 and 27 to find the answer to this.

    Thanks! Back to reading....

    You understood my question\s perfectly. I was assuming the GSU-25 was not needed because I thought WAAS altitude is more accurate than pressure altitude and it seemed kind of silly to provide pressure altitude to the transponder when it already had more accurate altitude provided by the GPS. But sounds like in this configuration its not as accurate so altitude is provided by GSU-25.

    So I found on the FCC website the installation manual for the GTX45R that is version 2. Garmin only list version 1 on their website??? So anyone installing a GPS20A and a GTX45R or here is the interconnect drawing. Also if you are wondering what the A/c Suppression BUS is? Answer listed below.


    Thanks for your help PapuaPilot. I am running the GTX45R transponder and it does not appear to have a CANBUS connection. I am assuming that the GTX45R communicates to the G3X via the 232 that I hook up to it. Seems weird there is no canbus to it?

    Also once you have the GPS-20a connected properly does it provide position source to the G3X if I am not running anything else like a GTN650 or GNS430/530 ect?

    Last thing to figure out. I think the GPS-20a can provide gps position to my ELT? Next thing to figure out. I need to dig into the ELT next but maybe the external suppression is used?

    The EXTERNAL SUPPRESSION is intended for connection to other L-band equipment, such as a DME
    or UAT. The output is active whenever the GTX 35R/45R transmits. When driven by another source, the
    GTX 35R/45R transponder receiver and transmitter functions will be suppressed.

    Capture.PNG
    Dustin Dickerson

    Building 7ss STI x 2
    Oratex
    29" shock monster
    EP912STI 155hp
    Garmin
    N33TF
    N53TF

  8. #18
    Senior Member PapuaPilot's Avatar
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    Default Re: Garmin G3x Wiring Questions

    Happy reading. The GTX45 is certainly different than my GTX23ES.
    Phil Nelson
    A&P-IA, Maintenance Instructor
    KF 5, Continental IO-240
    Flying

  9. #19
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    Default Re: Garmin G3x Wiring Questions

    You understood my question\s perfectly. I was assuming the GSU-25 was not needed because I thought WAAS altitude is more accurate than pressure altitude and it seemed kind of silly to provide pressure altitude to the transponder when it already had more accurate altitude provided by the GPS. But sounds like in this configuration its not as accurate so altitude is provided by GSU-25.
    Transponders work off 29.92 and then 'fudge' the result to get altitude. It would be no good providing a GPS altitude because (a)they're not as accurate as you think and (b)they're not working off a standard pressure setting, so everyone can be off by varying amounts. So you definitely need to provide your transponder with a pressure-based altitude, instead of GPS-based. Since the EFIS is plumber for pitot and static pressure it's quite normal to just have the transponder 'talk' to the EFIS over the CAN bus and gain the information it needs from there.

  10. #20

    Default Re: Garmin G3x Wiring Questions

    I currently am installing the GTX45R with the same equipment as you mention. Here's what I have...

    GTX45R >>> G3x
    30 41
    8 24
    51 35

    GTX45R >>> GSU25
    31 9
    9 10
    52 11

    GTX45R >>> GPS20A
    29 5
    50 6

    G3X >>> Artex 345 ELT
    48 9
    Building Model 6
    912 IS
    Garmin G3X
    http://northernfox.build
    C-FKLO

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