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Thread: What else could be the issue with my adsb?

  1. #1

    What else could be the issue with my adsb?

    RV-7A with an Advanced panel -2 AFS 5600, Garmin GTN650.
    Transponder is SV-XPNDR-261, ADSB module is the 470 and GPS signal is configured from GTN-650 to feed the system.
    My adsb is intermittent at best. Flightaware only shows me for very short sections of each flight. I have never been able to generate a PAPR for any flight - always says that it is not found. Traffic shows on my screens but disappears and reappears intermittently. I have several times had shadowing where I receive a traffic annunciation warning that there is another plane exactly where I am and at my altitude - but there is no other plane - it's just me. In Class B after takeoff, I was initially not able to be seen via adsb but they had my mode S readings. Eventually my adsb out showed up for the Class B controller but not right after takeoff and not consistently.

    What I have tried:
    Antenna placement - it is too intermittent for gear leg shadowing to explain all the failures and a PAPR would generate for at least part of the flight which it never does.
    GPS signal - I did troubleshooting with Jonathan by phone to ensure that the menus on my GTN 650 and the AFS screens were all set correctly, and they all are without fixing the problems.
    Flying in lots of places - I was concerned that antenna placement in my area may be sparse so I have tried it out in every area around me within a 2-hour flight time - no fix.

    So - what could be my issue? I don't feel I have reliable enough signal to transit Class B and I need to be able to do that along with not trusting that my traffic display is actually showing me all the available traffic.
    All I can come up with is that I need to replace my 470 adsb box with a 472 - but I don't want to spend that money and still end up without a solution. Does anyone have any ideas of what else I should be trying. I am glad to buy and replace anything to solve the issue but I can't figure out where to even start to get a solution. Thanks for any suggestions you might have.

  2. #2
    I forgot to mention that several times I have seen a yellow pop-up warning on my AFS screens that says "No ADSB Pos"
    The warning has only stayed on for about 10 seconds and then disappears on its own and does not repeat that flight. This has happened about 5 times in the last 6 months. It is usually shortly after takeoff or even while I am still on the ground.
    Maybe that is helpful diagnostically?

  3. #3
    Replacing the ADSB 470 with a 472 will improve your weather and traffic picture, but it will do nothing for the stated problems which are related to your ADSB out. The preponderance of evidence suggests that the GPS position from your GTN 650 is not getting to the transponder. This could be configuration or it could be wiring. Since it seems we have already gone through the settings, the next thing that you need to check is that the serial port wired out from the GTN is making it to pin 3 on the transponder, with specifically 1.21k ohms resistance provided via an external in-line resistor which must be added to the wire.

  4. #4
    Thanks Jonathon. I went ahead and upgraded to the 472 and got it installed today. I only tested it on the ground - will have to test fly when it is a bit less windy than today. On the ground pulled out of the hangar so that I could get GPS signal through the GTN650 I was able to see a lot more of the traffic in the skies above me. However, it seems to blink and I will go from 10 adsb targets to 0 and then after a few minutes I would go back to 10 targets again. Any thoughts on what would cause that sort of blink? I checked the connections from 472 to SV-XPNDR-261 and connection to the ACM control module and they were all solid and not loose. Would the pin 3 ohms resistance manifest like that?

  5. #5
    Still thinking it is a configuration issue instead of a wiring issue - I am using the ACM install manual and the AF-5000 Pilot's guide to configure menus. In the ACM Installation manual on pg 41 there are menu instructions for a "Dual EFIS Screen IFR Panel settings".
    Do those instructions apply to a dual efis panel with a GTN650 just as well as a dual efis panel using an IFD product? The port 3 value on that page is noted as "ADS-B data sent to IFD". On my menus, port 3 was disabled - if I change it to match the settings on pg 41 of the manual - will that address my issue or do I need different settings for a GTN650 vs an IFD?
    I matched all the settings on the GTN-650, so now I am just trying to ensure that all my admin settings and xpndr settings in the menus are also correct. Thanks for any clarification you may have.

  6. #6
    In the end it was not the wiring and it was not menu configurations. The software on my Dynon SV-XPNDR-261 was out of date. It was so out of date that it would not receive information from the GTN650. Once the software got updated on the transponder - everything works. I can generate PAPR reports and track using ADSB.
    A note on updating the software on the Dynon transponder. If you have Dynon screens, then you can update from that system. Unfortunately, the AFS screens do not allow you to update the software on the transponder. So, either get hooked into a Dynon screen or send it away to Dynon to get the software loaded.
    Thanks to Jonathon who helped me troubleshoot on the phone and eliminate issues until I was able to get an avionics shop to find the transponder software issue.

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