GDL39 Protocol

[chartbundle]

So, after hours of work I'm happy to announce a document on the basics of the GDL39 protocol as provided on the Bluetooth interface.

The upside is that it's pretty simple and does almost all the ADS-B and FIS-B decoding for you(no 6 bit alphabets or random lat+lon encoding)

The downside for iOS is that because it's Bluetooth it will require any vendor who wants to use it to have Garmin bless their application before it would be available in the App Store(which I don't think is likely since they don't seem to officially document the protocol.) This is one of the advantages of the devices using WiFi. For any other device(Android, PC, Mac) it's just as easy as a bluetooth connection.

I've not looked at the serial cable yet, but one is on order.

I'm sort of considering an Android app that can translate for WiFi apps but that's significantly more work than just decoding, maybe someone else will handle that part.

http://www.chartbundle.com/tech/gdl39/

 

[John221us]

Even if you were to get this working; if it ever got popular, Garmin would just do an update to the software and break it.

 

[Jay Honeck]

If you could help the folks at Naviator make their software work with the GDL-39, there are lots of us who would be grateful.

Sent from my Nexus 7 using Tapatalk 2

 

[zaitcev]

Awesome work. However, the handshake is omnious and tells us that Garmin intend to obfuscate on purpose. I'm wondering if we could talk Skyvision into opening up (http://skyvisionxtreme.com/).

 

[snoboy]

If you could help the folks at Naviator make their software work with the GDL-39, there are lots of us who would be grateful.

Sent from my Nexus 7 using Tapatalk 2

I second that as I have Naviator and Garmin Pilot. Love them both Naviator for ease of use and Garmin for it's super duper secondary layers, ie fuel prices, lightning, streaming doppler. The GDL39 would work so perfect for me. Jay do you have the GDL 39 and can you share some pros and cons?

 

[Jay Honeck]

Jay do you have the GDL 39 and can you share some pros and cons?

WRT the GDL-39...

Weather: free is good!

Only downside, and it's well documented, is that you don't get the weather until airborne. Otherwise, I run it side-by-side with XM (on my 496) and it's fine -- and the price is right.

BTW: weather is also MUCH better overlaid on my moving map sectional, using the Nexus 7, than it is on my itty-bitty 496's screen.

Traffic: Not there yet. When it works, it's way cool, but you have to be near traffic that is squitting ADS-B out to fire up the ground stations. Not a lot of them floating around...yet. This will improve over time.

Usability: Excellent. It Bluetooths to my Nexus 7 without fuss, and plugs into the cigar lighter without too much muss. I am going to have it hard wired to ship's power next time I've got Atlas I'm the shop, though, just to eliminate the wire.

Overall I am very happy with it. When Garmin updates their Pilot software to recognize the Nexus 7 as a tablet (enabling split screen overlays) this set up will be perfect. Right now we must toggle between navigation and map screens, because the software thinks the N7 is a cellphone -- a real PIA. Garmin says the update is coming "soon"...

Sent from my Nexus 7 using Tapatalk 2

 

[snoboy]

Thanks for the insight.

 

[JGoodish]

Only downside, and it's well documented, is that you don't get the weather until airborne. Otherwise, I run it side-by-side with XM (on my 496) and it's fine -- and the price is right.

BTW: weather is also MUCH better overlaid on my moving map sectional, using the Nexus 7, than it is on my itty-bitty 496's screen.

Traffic: Not there yet. When it works, it's way cool, but you have to be near traffic that is squitting ADS-B out to fire up the ground stations. Not a lot of them floating around...yet. This will improve over time.

I recently discovered that there is a low-altitude ADS-B transmitter next to my house, so I do get weather on the ground. If your app can overlay Internet weather, and you have an Internet connection, this particular limitation of ADS-B may not be a huge deal in most situations.

As has been discussed in other threads, keep in mind that if you receive traffic from a ground station in response to someone else's "ping," the traffic response will be tailored to THEIR location and not yours. That means that you will likely be missing some traffic unless you are in close proximity to the aircraft whose response you intercepted. The obvious near-term solution to this problem is to equip your aircraft to transmit ADS-B Out, though I'm not sure that it's worth the expense right now just for the traffic display. When more of the fleet is equipped, I suspect that the air-to-air reception on 1090MHz will become more useful, but that's likely to be several years away.


JKG