Need Help Troubleshooting Garming GDL 39 3D Unit

Sinistar

Sinistar

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Brad
I purchased a used GDL 39 3D unit and got in one test flight before I went on vacation.

What Works On The Ground (At Home):
1.) GPS locks on nicely
2.) Traffic shows up - how is this even possible without locking onto a GBT?
3.) The synthetic vision works
4.) Worked with 2 androids simultaneously
NOTE: Wx did not work but I didn't expect it to.

What Works Up In the Air (I was flying at 4500agl)
1.) GPS locks on nicely
2.) Traffic shows up
3.) Synthetic vision worked but was very fussy (not all that important though).

What Did Not Work:
1.) Wx (is this the FIS-B)?

Now that I am back I looked and I see I was about 35miles from one ADS-B out tower and probably 50 miles from 3 more ADS-B out towers and the nearby Bravo.

So how is it possible that the traffic (TIS-B) is working (even on the ground) but the weather (FIS-B) is not working? Aren't they on the same antennae?

To verify, if I were to drive and park a few blocks from that closest tower should I be receiving on the ground? Or is the transmission focused do directly upward that there would be no reception on the ground? When testing on the ground is there a good distance to be away from the tower?

The E-Bay seller seems pretty cool and will refund the money, but I don't want to return it only to get another and find the same issue again such as if it is the plane or coverage where we live. We mainly bought it for wx and traffic and I don't want to keep it if the wx doesn't work.

Any help would be appreciated!
 
Using Garmin Pilot on a tablet, I had to change a setting to show weather as FIS-B, not the internet.. when connected to the GDL39. Looking for that setting on my phone, I do not see it, running GP 6.3.1... it may have changed, but my phone is not set up to use the GLD39 in my plane... just my tablet. Thus if the GDL39 dies, my phone will be setup as a backup not needing that input.. Check for a setting that will drive weather to FIS-B, GDL39 in place of the internet...
 
Sinistar said:
To verify, if I were to drive and park a few blocks from that closest tower should I be receiving on the ground?
Click to expand...

Sinistar said:
When testing on the ground is there a good distance to be away from the tower?
Click to expand...

The ADS-B signals are line of sight. With the dual band unit, you will see air-to-air ADS-B Out. To see TIS-B / ADS-R, or FIS-B, you will need to be within 5 - 10 miles of the tower when on the ground.

Sinistar said:
Or is the transmission focused do directly upward that there would be no reception on the ground?
Click to expand...

The tower antennas are designed to point the signal skyward to cover their respective service areas at altitude. This reduces that amount of signal available from the ground.
 
Sinistar said:
So how is it possible that the traffic (TIS-B) is working (even on the ground) but the weather (FIS-B) is not working?
Click to expand...
As stated above, when setting on the ground (or in the air for that matter), the traffic information can be received directly as 1090 ES or 978 UAT ADS-B Out squitters from the airborne ADS-B emitters (transmitter). The traffic information is also received as TIS-B / ADS-R data via the Ground Based Tower (GBT). For the tower to broadcast the traffic information, it needs to receive a request from a compliant ADS-B Out emitter. If it doesn't receive the request the traffic information is suppressed during the tower broadcast. If an aircraft is not ADS-B Out equipped, it will need to be within a "Hockey Puck" of a compliant ADS-B Out aircraft to receive the GBT TIS-B / ADS-R broadcast.

Sinistar said:
Aren't they on the same antennae?
Click to expand...
Yes they but...
The FIS-B data is broadcast full time from the ADS-B tower. However, you will need to be within range of the tower to receive the line-of-sight ADS-B broadcast. Also, as previously mentioned, the TIS-B / ADS-R traffic data is broadcasted when the tower receives a broadcast request from a compliant ADS-B Out emitter.
 
Axtel4 said:
The ADS-B signals are line of sight. With the dual band unit, you will see air-to-air ADS-B Out. To see TIS-B / ADS-R, or FIS-B, you will need to be within 5 - 10 miles of the tower when on the ground.

...

The tower antennas are designed to point the signal skyward to cover their respective service areas at altitude. This reduces that amount of signal available from the ground.
Click to expand...

None of the antenna arrays at the local tower have any mechanical uptilt and I doubt they’re using electrical uptilt. But I could ask someone. They look like bog standard gain to the horizon antennas to me, and altitude takes care of the rest.

You’re correct about the on the ground and low level coverage. Normal distance squared rule and ground clutter and terrain blocking rules apply there. Remember these signals are up around 1 GHz and they behave accordingly.
 
Axtel4 said:
Also, as previously mentioned, the TIS-B / ADS-R traffic data is broadcasted when the tower receives a broadcast request from a compliant ADS-B Out emitter.
Click to expand...

To be clear here also, it’s not really a request. The system just tracks locations of targets transmitting ADS-B Out and broadcasts only traffic in a certain radius around that traffic.

It’s a dangerous and stupid design for a safety system. It should transmit all traffic at all times in the coverage area of the antenna. Any aircraft can have an ADS-B Out transmitter failure and lose surrounding traffic if they’re not in someone else’s “puck”. For all the hype and marketing about it being a safety system, the puck is a fatal design flaw and should be eliminated.
 
denverpilot said:
None of the antenna arrays at the local tower have any mechanical uptilt and I doubt they’re using electrical uptilt. But I could ask someone. They look like bog standard gain to the horizon antennas to me, and altitude takes care of the rest.
Click to expand...

On this, we are going to have to disagree. The performance plots for a ground station antenna supplier shows their maximum gain at 0 degrees vertical. The gain decreases 3 dB at approximately +/-20 degrees from vertical while decreasing 3 dB further approximately +/- 45 degrees from vertical. At +/-90 degrees from vertical, the gain is approaching 20 dB below the maximum 0 degree vertical gain. Also, depending on the antenna model, the takeoff angle is between 5 degrees to 11 degrees above the horizon.

The "eletrical uplift" is accomplished by the phase shift between the segments within an antenna element.
 
Axtel4 said:
On this, we are going to have to disagree. The performance plots for a ground station antenna supplier shows their maximum gain at 0 degrees vertical. The gain decreases 3 dB at approximately +/-20 degrees from vertical while decreasing 3 dB further approximately +/- 45 degrees from vertical. At +/-90 degrees from vertical, the gain is approaching 20 dB below the maximum 0 degree vertical gain. Also, depending on the antenna model, the takeoff angle is between 5 degrees to 11 degrees above the horizon.

The "eletrical uplift" is accomplished by the phase shift between the segments within an antenna element.
Click to expand...

Got a link? I know how electrical uptilt works. I want to see this thing, because I've seen the ones on the local ADS-B tower, and they're not oriented or the type that would accomplish that. Not even close.
 
View attachment 60896
denverpilot said:
To be clear here also, it’s not really a request. The system just tracks locations of targets transmitting ADS-B Out and broadcasts only traffic in a certain radius around that traffic.
Click to expand...

A matter of semantics. In general terms it is a "request". If the ground station does not receive the UTI / ESI bit in the DF 17 message, i.e. a "request" from the ADS-B Out aircraft, it will not respond with TIS-B / ADS-R broadcast. For 1090ES aircraft reference "Capability Class" in DO-260B and "Capability Codes" in DO-282B.

From FAA FAA-E-3006:
The TIS-B Service shall suppress a TIS-B target scheduled to be transmitted to ADS-B targets that are reporting Receive Capability equal to “NO” in Version TWO (2) Messages per DO-282B or DO-260B.

Note: The TIS-B Service does not provide TIS-B Service to ADS-B targets equipped to only transmit (i.e., ADS-B OUT). DO-282B and DO-260B have new message fields to indicate whether the ADS-B target is ADS-B OUT only or also ADS-B IN capable. ADS-B targets that ADS-B IN capable only is not an acceptable configuration to receive TIS-B Service. This requirement does not apply to Version One (1) UAT or 1090ES equipped targets.
Click to expand...


denverpilot said:
It’s a dangerous and stupid design for a safety system. It should transmit all traffic at all times in the coverage area of the antenna. Any aircraft can have an ADS-B Out transmitter failure and lose surrounding traffic if they’re not in someone else’s “puck”. For all the hype and marketing about it being a safety system, the puck is a fatal design flaw and should be eliminated.
Click to expand...
No argument here.
 
I opened this because I expected to see 39 triple D units.
 
Axtel4 said:
One such vendor: http://www.dbsant.com
Click to expand...

Not a well know brand that I’m aware of. Do you have any indication they’re actually selling the things in quantity to FAA?

Should be possible to see who’s winning the bids on the antenna contracts unless they’re being bundled by an installer into a package.

Or... via press releases. Most vendors crow loudly when they win.

The website is somewhat meaningless.
 
First off a big thanks to @John Collins on his other thread with a updated list of the GBT locations...awesome!!! I loaded up Google Earth and found that one was on my way to work! There are 3 more at the Bravo and then a decent number north and south but pretty barren going west of us until Sioux Falls area.

Glenn D said:
Using Garmin Pilot on a tablet, I had to change a setting to show weather as FIS-B, not the internet.. when connected to the GDL39. Looking for that setting on my phone, I do not see it, running GP 6.3.1... it may have changed, but my phone is not set up to use the GLD39 in my plane... just my tablet. Thus if the GDL39 dies, my phone will be setup as a backup not needing that input.. Check for a setting that will drive weather to FIS-B, GDL39 in place of the internet...
Click to expand...
Actually Glenn, it is still in 6.3.1. It is on the overlays selection menu where you can select "Internet" or "ADS-B" for the radar. So this selection appears to be for radar only. Mine was on internet and during my ground test near the GBT tower I switched to "ADS-B" and within a few second I saw some precip up in the UP of Michigan (I was about 20m SW of Minneapolis).

I was getting a bit worried about airport weather showing up, seemed like it took well over 2 minutes. Then the metar info I had selected showed up next to every airport in at least a 150nm range. Okay...its working.

And since I was about 10miles from a Delta. I finally saw the TIS-B icon light up and could actually see two planes actually doing finals and some taxi on the runway. Its as if once they slowed down below a certain speed they stopped squitting out their location. Had there not been two together I probably wouldn't have seen either, especially when they were only 800agl and I was 10 miles away.

So now the dilemma. It works on the ground but didn't seem to work up in the air. I will test fly it again and know better what to look for and when. It is possible the dash of the 182 just isn't practical in which I might need an external antennae (belly mounted?). If that is case I don't want to go with the portable. I'll add an update to the thread once I test fly it again. My wife claimed she's flying next so I can just and tinker with gadgets while she gets current again LOL :)
 
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