SmilingJack

SmilingJack

Well Known Member
Has anyone come across this? No METAR?

I have a GDL39 feeding a G3X

iphone app pic of the status


Another shot of the G3X



I just installed ADSb OUT using a GTX330 and confirmed I am 100% operational, but the GDL39 now see me as a TARGEt :eek:
 
I'm using a GDL39 with a Garmin 795 and occasionally see myself as a target with a traffic warning. I guess an ADSB-in(only) system doesn't differentiate your own return from any others locally, especially if you're only Mode A/C equipped.

I think there is an algorithm that works out that an aircraft in the same place and moving at the same speed as you is probably your own aircraft and filters it out, but the ADSB target has a delay and there could be a position error between the SSR position and Mode C altitude that the radar sees and the GPS position and altitude of your own equipment, and if that difference is sufficient then it assumes that it's a different aircraft.

I had my ghost ship chasing me but 200' below. It can grab your attention at first!
 
I am thinking a future upgrade could allow us to place a Tailnumber in the GDL39 to filter out it's own aircraft.

I was flying most of the trip with the traffic warning screen on and am not sure if it filters out/declutters others....
 
Did you do the ADS-B setup in the G3X?

Page 27-102 of the manual (rev M)
27.4.15 ADS-B Configuration Page
 
SmilingJack said:
Has anyone come across this? No METAR?

I have a GDL39 feeding a G3X

iphone app pic of the status


Another shot of the G3X



I just installed ADSb OUT using a GTX330 and confirmed I am 100% operational, but the GDL39 now see me as a TARGEt :eek:
Click to expand...

Hello John,

In the interest of keeping the facts straight, you have a GDU 375 display and not a G3X system (yet).

We need to get you to install the GSU25, connect the GTX330ES to the GSU25, and then the G3X system will send your ICAO address to the GDL39 and you will be like the rest of us G3X pilots who never see a false traffic alert on ourselves.

Having said that, what you are seeing is very unusual and perhaps attributable to the uncommon non-Garmin position source you are using on the GTX330ES.

I also fly 100% of the time with an Aera 560 connected to a second GDL39 that doesn't know my ICAO address and it only rarely provides a false traffic alert (generally when maneuvering), so Mark may be onto something that there is a significant position delay somewhere in your system.

Your GDL39 is getting very accurate real-time position data from the GDU 375, and if this deviates significantly from the position reported by your ADS-B Out, the ownship determination logic in the GDL39 may be failing to identify you. I have never heard of anything like you describe, so this is very likely attributable to your ADS-B Out position source.

As you can imagine, if your ADS-B Out position puts you far enough away from the GDU 375 determined position, in the interest of safety, the GDL39 needs to identify you as an intruder!

Thanks,
Steve
 
Garmin Pilot

I have had this happen a few times using Garmin Pilot app with my Ipad and a GDL39. It got my attention at first. I had to dismiss the warning because it takes over the whole screen
 
Steve, I wish I had the space for the GSU25!

So, with the single screen setup it seems I can NOT put my mode S address in :(

I know...I am the odd man here with my GDU375...

I rechecked my flight data and found the first hour I had the previous picture shown, then the last hour near Tampa the system seemed NOT to show a traffic warning for myself:



Last, I did receive a response from "Jim" at the FAA and my ADSb was good and passed.

Are you sure your software guy cant give us GDL39 guys a way to address it? :D
 
SmilingJack said:
Steve, I wish I had the space for the GSU25!

So, with the single screen setup it seems I can NOT put my mode S address in :(

I know...I am the odd man here with my GDU375...

I rechecked my flight data and found the first hour I had the previous picture shown, then the last hour near Tampa the system seemed NOT to show a traffic warning for myself:


Last, I did receive a response from "Jim" at the FAA and my ADSb was good and passed.

Are you sure your software guy cant give us GDL39 guys a way to address it? :D
Click to expand...

Hello John,

We decided up front that any use of a GDL39 with portables would use automatic ownship detection instead of forced "here is your ownship address" operation.

This was done to keep the setup simple with portable devices and prevent the potential of someone accidentally filtering out another aircraft.

In a G3X system, we know your aircraft address because we are talking to your Mode S transponder, so we automatically provide it to the GDL39 without any operator involvement and it is a very robust solution.

Correction from earlier post - You are in luck! The GDU 375, even when used outside of a G3X system, allows you to enter the Mode S address for your aircraft on the ADS-B Data Link Configuration page and reject traffic targets which have your address. Walt had the answer.

Thanks,
Steve
 
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While we have Steve on the thread I will drift a bit.
I have had my traffic working flawless until I started some formation flight.
At the wing position I had the transponder turned to standby and did not have good traffic. This I understand. However when I turned it back on during flight the no-signal icon stayed x'd and I did not get good traffic. This did not improve until I flew my next flight. This has now happened a few times.
Any thoughts?
 
MarkW said:
While we have Steve on the thread I will drift a bit.
I have had my traffic working flawless until I started some formation flight.
At the wing position I had the transponder turned to standby and did not have good traffic. This I understand. However when I turned it back on during flight the no-signal icon stayed x'd and I did not get good traffic. This did not improve until I flew my next flight. This has now happened a few times.
Any thoughts?
Click to expand...

I have had a few issues as well trying to use TIS-B when flying with wingmen.

In my case I am the only one with 1090ES ADS-B out and the others have only been Mode-C.

Anytime I try to fly in what I call loose formation with them and they have their xponders on, it will confuse my system and cause me to lose the TIS-B uplink. If I have em switch their xponders into standby, we can fly all day in loose formation and I won't have a problem.

If my buddies always stay at least a half mile away from me, even with their xponders on, I do not experience any issues so it appears to be proximity related with how the system filters out my ownship and how it deals with other targets when they are close in. I think somewhere in the system it thinks I am them or vice versa and or the ground station data is getting confused.

It is much worse if the wingman wanders around from loose to looser to loose formation. The system does not seem to deal with that very well. They will disappear, reappear, disappear and then eventually the system will go INOP on the uplink.

So now I just have em turn off their xponder and I call out traffic to the group. I know where they are so it does not bother me that they do not show up....
 
Brantel said:
I have had a few issues as well trying to use TIS-B when flying with wingmen.

In my case I am the only one with 1090ES ADS-B out and the others have only been Mode-C.

Anytime I try to fly in what I call loose formation with them and they have their xponders on, it will confuse my system and cause me to lose the TIS-B uplink. If I have em switch their xponders into standby, we can fly all day in loose formation and I won't have a problem.

If my buddies always stay at least a half mile away from me, even with their xponders on, I do not experience any issues so it appears to be proximity related with how the system filters out my ownship and how it deals with other targets when they are close in. I think somewhere in the system it thinks I am them or vice versa and or the ground station data is getting confused.

It is much worse if the wingman wanders around from loose to looser to loose formation. The system does not seem to deal with that very well. They will disappear, reappear, disappear and then eventually the system will go INOP on the uplink.

So now I just have em turn off their xponder and I call out traffic to the group. I know where they are so it does not bother me that they do not show up....
Click to expand...

Thanks, Brian

It does seem that the most capable ADS-B Out aircraft in a formation, or even a loose formation, is ideally the only aircraft transmitting to keep everything working well.

If you inhibit traffic alerts from the traffic page on the non-transmitting aircraft, they can still gain the benefits of receiving and seeing traffic without being pestered about the lead aircraft.

We looked in the AIM recently for guidance on transponder operation in formation flight, but didn't find much information. We did find this in New Zealand guidance:

Unless otherwise required by ATC, only one of the aircraft in a formation flight is required to operate a transponder...
​
Thanks,
Steve
 
Just a general comment for those on the fence. The GDL39 is a smart addition to any Garmin... portable or not.
I think the traffic alerts are a bonus... situational A etc.
The WX link is quite valuable right now in summer.
The cost is low... wiring simple. I use a $10 transponder stub on the belly... always picking up multiple stations.
Mount the 39 under the panel where it is cool... and feed GPS position to it from another source. EASY
 
Brian,
Hmm. Mine does not seem to act as if proximity related. I most always have them on the screen just not always a warning. I do always keep a good signal unless starting the flight with the Transponder off. Once I have the problem I can not regain the signal.
 
Mark,
Try turning the transponder off for at least 12 seconds when far apart from other aircraft (well after you break the formation).

If you turn the transponder on while in formation then break it, you can confuse the ADS-B ground station correlation algorithms and it may actually think you are one of the other planes until it loses lock with you.

Just a thought based on my experience with ADS-B, albeit with a different system.
 
So Dy, you are saying that I may have turned it on while still close to the other outputting aircraft. That I should either wait until I clear them or if I inadvertently goof I can probably turn it back to stdby, wait a moment and then turn back to altitude?
Makes sense so I will give it a try and report back. Thanks.
 
Mark, yes, that is what I am suggesting. No guarantee it will work, but I have seen taking the transponder off line and bringing it back make a difference before. Normal enroute radars sweep at about 10 seconds per revolution and you need to be gone for at least two sweeps to get dropped so that you will get re-initialized when you turn back on.
 
http://www.avionictools.com/icao.php

Thanks to Walt and Steve I think I (they) have solved my problem.

My HEX address was all wrong in my GDU375!

good thing the airplane that had the HEX address I "made up" was no where around me or he would have been stealth to me :eek:

Now I have my excuse to go test fly it tomorrow :D
 
Success!

Couple airplane far away:



Not much traffic today so I had to pan out and go unrestricted:



Very happy to get the ADSb OUT up and running
 
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