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01-21-2013, 04:30 PM
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Join Date: Jun 2005
Location: Chino, CA
Posts: 738
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Traffic alert - me
I have a GDL-39 bluetoothed to my 796. My transponder is GTX327 (no TIS).
I have never seen the TIS-B uplink on the 796 show anything but an X,
yet yesterday between Santa Barbara and San Luis Obispo, I recieved
a traffic alert. -01 (100 ft below) and on my immediate 6  After
a quick right turn, it disappeared. After turning back on course, it reappeared
for a few seconds. I know this was a shadow. I had to be recieving
TIS-B thru the GDL-39 as I have before in the LA basin. But my TIS-B
flag on the 796 (and my iPad w/garmin pilot) always have an X in the box.
What gives?
__________________
Tom Prokop
Chino, CA
RV-8A,180/CS/Carb, AFS 4500 EFIS/EMS
RV-6, sold, 820 hrs of fun.
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01-21-2013, 06:04 PM
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Join Date: Mar 2006
Location: Newport, TN
Posts: 7,496
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Quote:
Originally Posted by Bushcaddy
I believe the GPS is wired both ways, that was part of the discussion I had w/the avionics shop prior to getting the ES upgrade. I just sent the shop an email to confirm this and to ask what the Xpdr settings should be so I can double check it.
I did not know that my current configuration...GDL 39/GTX 330 ES/Aera 796, would not be compliant in 2020 though?????
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No sir it won't. The 796 will most likely never be certified as meeting the 2020 position source requirements.
As far as I know, the 330ES requires at least Aviation format to get a position source from a GPS and the preferred protocol is Garmin's ADS-B format.
The 796 can only provide NMEA out and that protocol does not have enough information in it to provide the 330ES what it needs to fill out the ES data set.
I am making some assumptions here because I don't have a 330ES installation manual. I may be wrong but I am betting I am close to the root of the issue....
Last edited by Brantel : 01-21-2013 at 09:08 PM.
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01-21-2013, 06:55 PM
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Join Date: Aug 2005
Location: Dallas/Ft Worth, TX
Posts: 5,686
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True, none of the Garmin transponders will accept the NMEA GPS data which is provided by portable GPS products. So, for example, you would not be able to connect a GPSMAP 696/796 to a GTX330ES as the position source.
__________________
Walt Aronow, DFW, TX (52F)
EXP Aircraft Services LLC
Specializing in RV Condition Inspections, Maintenance, Avionics Upgrades
Dynamic Prop Balancing, Pitot-Static Altmeter/Transponder Certification
FAA Certified Repair Station, AP/IA/FCC GROL, EAA Technical Counselor
Authorized Garmin G3X Dealer/Installer
RV7A built 2004, 1700+ hrs, New Titan IO-370, Bendix Mags
Website: ExpAircraft.com, Email: walt@expaircraft.com, Cell: 972-746-5154
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01-21-2013, 07:14 PM
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Join Date: Sep 2010
Location: Olathe, KS
Posts: 2,885
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Quote:
Originally Posted by Bushcaddy
I believe the GPS is wired both ways, that was part of the discussion I had w/the avionics shop prior to getting the ES upgrade. I just sent the shop an email to confirm this and to ask what the Xpdr settings should be so I can double check it.
I did not know that my current configuration...GDL 39/GTX 330 ES/Aera 796, would not be compliant in 2020 though?????
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Hello Don,
You have a great setup for receiving and displaying ADS-B traffic and weather, but these posters are correct that the NMEA output from the Aera 796 cannot be used to supply position and other data to the GTX 330 ES.
We suspect that the serial connection between your GTX 330 ES and the Aera 796 is one direction only and transmits TIS-A traffic data from your GTX 330 ES to the Aera 796.
Thanks,
Steve
__________________
Garmin G3X Support
g3xpert@garmin.com
1-866-854-8433 - 7 to 7 Central Time M to F
Please email us for support instead of using Private Messaging due to the limitations of the latter.
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01-21-2013, 08:14 PM
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Join Date: Jul 2008
Location: Plymouth, MA
Posts: 133
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Steve thanks for the follow up. I guess my question is what was the advantage of getting the ES upgrade to my GTX 330 if it couldn't take a position fix from my gps? I was under the impression (from my avionics shop) that the 3 components (GTX 330, GDL 39 and 796), working together, would give me ADS-B in and out. It appears that the only traffic I'll be getting is what I was already getting from my 330 before spending the $1200 on the upgrade. Am I incorrect? What am I missing? Thanks...
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01-21-2013, 09:05 PM
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Join Date: Mar 2006
Location: Newport, TN
Posts: 7,496
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Your not getting much if you do not have the proper position source available for your GTX330ES other than you will be ready for 2020 when you install such a source.
It is unfortunate that your avionics shop misinformed you. I suspect this is fairly common these days since this ADS-B stuff is so new.
Hopefully soon there will be lower cost options for a certified position source available. When there are, as long as Garmin supports them, you will be ready to go....until then your option is to install a GPS (or a G3X system) that meets the needs of the GTX330ES.
Last edited by Brantel : 01-21-2013 at 09:10 PM.
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01-21-2013, 09:11 PM
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Join Date: Mar 2006
Location: Newport, TN
Posts: 7,496
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Quote:
Originally Posted by Chino Tom
I have a GDL-39 bluetoothed to my 796. My transponder is GTX327 (no TIS).
I have never seen the TIS-B uplink on the 796 show anything but an X,
yet yesterday between Santa Barbara and San Luis Obispo, I recieved
a traffic alert. -01 (100 ft below) and on my immediate 6  After
a quick right turn, it disappeared. After turning back on course, it reappeared
for a few seconds. I know this was a shadow. I had to be recieving
TIS-B thru the GDL-39 as I have before in the LA basin. But my TIS-B
flag on the 796 (and my iPad w/garmin pilot) always have an X in the box.
What gives?
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Tom,
Are you saying you have never not seen the X on the TIS-B box? Even when you were actually receiving TIS-B? I have piggy backed several times and the X goes away during that time.
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01-22-2013, 07:02 AM
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Join Date: Jan 2005
Location: Tulsa, OK
Posts: 1,015
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Interesting thread
Trying to understand how this is all supposed to work as I have a similar (but not exactly the same) situation as the poster. I have 796, GDL-39 and GTX-327 and all are hard wired together. The TIS-B is always X'd out and I have not yet seen any targets displayed on the 796 even when I flew to the Dallas area last weekend. I have the GDL-39 diagnostic app on my iPad and at the same time I had nothing on the 796 the app showed good signals from 3 ground stations and that it was tracking 30 targets.
If the iPad app was tracking targets from the GDL39 should there have been something on the 796? Range rings on the 796 were 2M and 6M and the filter settings were set on Normal so I assumed the targets were outside the range setting.
I was getting ADSB weather such as METARS etc.
What causes the TIS-B to become active 
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01-22-2013, 07:18 AM
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Join Date: Mar 2006
Location: Newport, TN
Posts: 7,496
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Quote:
Originally Posted by uk_figs
Trying to understand how this is all supposed to work as I have a similar (but not exactly the same) situation as the poster. I have 796, GDL-39 and GTX-327 and all are hard wired together. The TIS-B is always X'd out and I have not yet seen any targets displayed on the 796 even when I flew to the Dallas area last weekend. I have the GDL-39 diagnostic app on my iPad and at the same time I had nothing on the 796 the app showed good signals from 3 ground stations and that it was tracking 30 targets.
If the iPad app was tracking targets from the GDL39 should there have been something on the 796? Range rings on the 796 were 2M and 6M and the filter settings were set on Normal so I assumed the targets were outside the range setting.
I was getting ADSB weather such as METARS etc.
What causes the TIS-B to become active 
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Yes, most likely the filter settings were different on the 796 vs the Ipad app. Most likely what you were seeing on the Ipad were air to air targets which does not require anything other than the GDL39 to receive.
To get TIS-B, something must wake up the ground stations and get them to send you the TIS-B traffic info.
To wake them up you need an ADS-B out device like an ES enabled mode S transponder or a UAT. Both of these will wake up the ground stations and get them to send you traffic info.
The other less desirable way is to piggy back on an aircraft near you that has ADS-B out. If you are close enough, you can steal the traffic info being provided for that aircraft.
The bottom line is that the GDL-39 is a receiver only and the GTX327 is not an ES enabled mode S transponder.
By 2020 if you want to fly anywhere a mode C transponder is required today, you will be required to be ADS-B out enabled. This means that you will either need to replace your GTX327 with a ES enabled mode S transponder or install a UAT. Both of which will require a certified position source capable of meeting the 2020 standards (the 796 won't do that).
I can tell you this...once you start receiving TIS-B traffic, you will be amazed at how much traffic there is out there.....
Last edited by Brantel : 01-22-2013 at 11:09 AM.
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01-22-2013, 07:26 AM
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Join Date: Mar 2006
Location: Newport, TN
Posts: 7,496
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For all with questions about ADS-B, Garmin has an entire mini site dedicated to the subject:
Click to go there...

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