GDL90 in Navigator?

[Dan Kvinge]

I have been using Navigator on an iPhone in my glider for a couple years now and like it, and it continues to get better.    I addressed the overheating (mostly) with a small USB fan.   I know Navigator has OGN, and I read about Flarm, but has anyone heard if there are plans to add GDL90 input to Navigator?   Where I fly in Minnesota/Wisconsin there are few aircraft with Flarm or OGN, but most have ADSB out.  It’s also easy to get a receiver that catches both 978 and 1090 MHz (unlike Power Flarm which only sees 1090 MHz).   

[Andy Blackburn]

The short answer I think is no. 

I looked at this in detail 5-6 years ago. GDL90 is a Garmin standard for communication of position data. Gliding instruments use NMEA which is the nautical standard. I was trying to add UAT traffic to the 1090ES traffic on Flarm. I was able to convince one of the Stratux developers to add NMEA sentences to the output on the ethernet port and then used a K6Mux to add it to the Flarm data stream. We tested it and it worked for any device connected to the RJ45 output of the Mux. The problem you get into just Muxing data streams together is that there is no de-duplication of targets that show up on multiple position systems. Ultimately Stratux ended support for the feature and about the same time Flarm added ADS-R support (I did the testing for them since there is not ADS-R in Europe because there is no UAT).

You have several options:

1) Install ADS-B Out on your Mode-S transponder and make sure your Flarm supports ADS-R (I think all PowerFlarms support it). This will allow you to pick up UAT targets and ADS-B rebroadcast on 1090ES from the ADS-B ground station network. You will also get TIS-B rebroadcast of SSR transponder-only aircraft - of which I hope there are very few remaining on exemptions of one sort or another.

2) Get a copy of Foreflight and get a separate dual-band ADS-B receiver to connect to it.

3) Get a StarLink Mini and connect to OGN and set your viewer to show all targets, not just gliders. I’m not sure if Navigator allows you to select targets by aircraft type or filters at all. Maybe someone else knows. ADS-B targets are injected into OGN via a setup Davis Chappins is hosting out of his room in Phoenix. It seems to work well, but like everything OGN it’s not FAA-approved collision avoidance - it’s traffic awareness. Or if you can wait a few months T-Mobile is starting to offer Direct To Cell (DTC) connectivity to your phone via StarLink as well.

Hope that helps.

Andy Blackburn

9B

On Feb 9, 2025, at 10:36 AM, Dan Kvinge <dank...@gmail.com> wrote:

I have been using Navigator on an iPhone in my glider for a couple years now and like it, and it continues to get better.    I addressed the overheating (mostly) with a small USB fan.   I know Navigator has OGN, and I read about Flarm, but has anyone heard if there are plans to add GDL90 input to Navigator?   Where I fly in Minnesota/Wisconsin there are few aircraft with Flarm or OGN, but most have ADSB out.  It’s also easy to get a receiver that catches both 978 and 1090 MHz (unlike Power Flarm which only sees 1090 MHz).   

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[Dan Kvinge]

Andy B, 

Referring to your points:

- We have Power Flarm in our trainer and it does pick up ADSB-Rebroadcast, but it is very unreliable when you are at the limit of the signal and also at lower elevations.   I think is just window-dressing by Flarm for the USA. It's almost dangerous since it sounds good, but really can't be trusted. 

- Yes, I can run Foreflight, or other products, in my glider, but I already use NAVIGATOR. I don't want to add another one (cost, screen distraction, space, etc).

-  I don't care about OGN or Flarm targets, there are almost none around me, but there are lots of GA at my airport and airspace and they use ADSB.

- What happened 5-6 years ago with ADSB is pretty old news now....ADSB is worldwide, reliable, growing everywhere.    Gliders everywhere need to embrace it.

Dan

[Andy Blackburn]

Sent from my iPhone

On Feb 9, 2025, at 8:08 PM, Dan Kvinge <dank...@gmail.com> wrote:

Andy B, 

Referring to your points:

- We have Power Flarm in our trainer and it does pick up ADSB-Rebroadcast, but it is very unreliable when you are at the limit of the signal and also at lower elevations.   I think is just window-dressing by Flarm for the USA. It's almost dangerous since it sounds good, but really can't be trusted. 

ADS-R is FAA’s solution for 1090ES and UAT interoperability. It’s not a Flarm technology. Flarm didn’t install hundreds of ADS-B ground stations in the US, the FAA did. If you think ADS-R coverage is poor you should contact your local FSDO because it means GA aircraft are also not seeing each other.

- Yes, I can run Foreflight, or other products, in my glider, but I already use NAVIGATOR. I don't want to add another one (cost, screen distraction, space, etc).

If you don’t like the FAA’s ADS-R and don’t want to use ForeFlight then you are screwed. The European glider guys aren’t going to fix the FAA’s kludgy dual-band implementation of ADS-B for them. They’re just not. The market is too small.

-  I don't care about OGN or Flarm targets, there are almost none around me, but there are lots of GA at my airport and airspace and they use ADSB.

OGN includes ADS-B targets. Use PureTrack if you want everything.

- What happened 5-6 years ago with ADSB is pretty old news now....ADSB is worldwide, reliable, growing everywhere.    Gliders everywhere need to embrace it.

ADS-B is a traffic advisory system designed to serve the FAA 3 mile/1000 foot separation philosophy. Flarm is designed to serve the 200 foot/0 foot glider separation philosophy.  You need to pick the system for your environment. If you fly with other gliders get a Flarm. If you are a sole glider flying with GA aircraft get ADS-B Out. 

I have both.

If you fly XC or race, get a Flarm. ADS-B won’t cut it.

Dan

On Sunday, February 9, 2025 at 1:58:11 PM UTC-6 Andy Blackburn wrote:

The short answer I think is no. 

I looked at this in detail 5-6 years ago. GDL90 is a Garmin standard for communication of position data. Gliding instruments use NMEA which is the nautical standard. I was trying to add UAT traffic to the 1090ES traffic on Flarm. I was able to convince one of the Stratux developers to add NMEA sentences to the output on the ethernet port and then used a K6Mux to add it to the Flarm data stream. We tested it and it worked for any device connected to the RJ45 output of the Mux. The problem you get into just Muxing data streams together is that there is no de-duplication of targets that show up on multiple position systems. Ultimately Stratux ended support for the feature and about the same time Flarm added ADS-R support (I did the testing for them since there is not ADS-R in Europe because there is no UAT).

You have several options:

1) Install ADS-B Out on your Mode-S transponder and make sure your Flarm supports ADS-R (I think all PowerFlarms support it). This will allow you to pick up UAT targets and ADS-B rebroadcast on 1090ES from the ADS-B ground station network. You will also get TIS-B rebroadcast of SSR transponder-only aircraft - of which I hope there are very few remaining on exemptions of one sort or another.

2) Get a copy of Foreflight and get a separate dual-band ADS-B receiver to connect to it.

3) Get a StarLink Mini and connect to OGN and set your viewer to show all targets, not just gliders. I’m not sure if Navigator allows you to select targets by aircraft type or filters at all. Maybe someone else knows. ADS-B targets are injected into OGN via a setup Davis Chappins is hosting out of his room in Phoenix. It seems to work well, but like everything OGN it’s not FAA-approved collision avoidance - it’s traffic awareness. Or if you can wait a few months T-Mobile is starting to offer Direct To Cell (DTC) connectivity to your phone via StarLink as well.

Hope that helps.

Andy Blackburn

9B

On Feb 9, 2025, at 10:36 AM, Dan Kvinge <dank...@gmail.com> wrote:

I have been using Navigator on an iPhone in my glider for a couple years now and like it, and it continues to get better.    I addressed the overheating (mostly) with a small USB fan.   I know Navigator has OGN, and I read about Flarm, but has anyone heard if there are plans to add GDL90 input to Navigator?   Where I fly in Minnesota/Wisconsin there are few aircraft with Flarm or OGN, but most have ADSB out.  It’s also easy to get a receiver that catches both 978 and 1090 MHz (unlike Power Flarm which only sees 1090 MHz).   

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[Dan Kvinge]

Words of Wisdom from Andy B:

“If you fly with other gliders get a Flarm. If you are a sole glider flying with GA aircraft get ADS-B Out. 

If you fly XC or race, get a Flarm. ADS-B won’t cut it.”

I agree completely!  

I think there’s a pretty big soaring population that only flies with GA, and never flies competition or ridges, and rarely shares thermals.  We would benefit from easier sharing of ADSB signals, and GDL90 is one seemingly pretty easy way.   

Back to my original post…I think if Navigator added GDL90 targets many would find a way to use it, and it would make Navigator more useful and valuable.  

I have been experimenting with PureTrack, and also AvTraffic.   They require cell data for me, but I usually have that where I fly.

Dan

[Paul Remde]

Hi Dan,

You may want to consider the new (available in the USA in a few weeks) FLARM PowerFLARM Flex.  It is a lower cost version of FLARM which has all the antennas built-in, and supports ADS-B 1090 reception and relayed ADSB UAT (ADS-R).  It can also connect to an Oudie N over Bluetooth.

https://www.cumulus-soaring.com/store/flarm-powerflarm-flex

I have a Flex prototype here at my home office if you want to see it sometime.  I think it will be popular as a low cost option - especially for soaring clubs.

Best Regards,

Paul Remde

Cumulus Soaring, Inc.

[moshe....@gmail.com]

You should be aware of SoftRF.  https://github.com/moshe-braner/SoftRF  It is an open-source traffic awareness and warning system which is 2-way compatible with FLARM.  You have to DIY put together the hardware, but it's only 5% of the cost of a Flarm Flex.  And, it now also allows you to add an ADS-B receiver module (does not transmit!), and SoftRF integrates the ADS-B traffic into the same internal table as the FLARM traffic.  SoftRF then reports all the traffic as FLARM-like NMEA sentences, via wired or wireless connection options, to whatever FLARM-compatible device you want, e.g., via Bluetooth to Navigator on your phone.  SoftRF with the add-on ADS-B module even receives UAT traffic if it's mirrored on 1090 via ADS-R.  With the ADS-B module added, the total hardware cost is, ahem, still less than just the cost of the ADS-R license for a FLARM.  Or, if you have a separate ADS-B receiver, hopefully dual-band, such as Stratux, SoftRF can accept the ADS-B traffic data from such a receiver, via wire or wirelessly, in GDL90 format.  The resulting output from SoftRF to your glide computer is still the FLARM-like NMEA.  (SoftRF also has a GDL90 output option, for other use cases.)

The language in FLARM's blurbs about ADS-R is misleading.  As Andy hinted, ADS-R only happens "by request" of a nearby aircraft.  If *you* don't have ADS-B out asking for it, you'll rarely receive any ADS-R transmissions.  In the early years almost all US GA that had ADS-B-out used 1090, so it seemed that just having 1090 reception on a FLARM was good enough. But in recent years UAT is getting more common, as lower-cost options have appeared.  This increases the pain of this split system.  In that sense an external dual-band receiver is the best solution if you're flying in the US-FAA's Rube Goldberg system, short of having ADS-B-out yourself. And BTW Andy: there are many GA planes around here with only an old-fashioned Mode-C transponder, no ADS-B.  No need for any waivers, they fly outside of Class A/B/C airspace, of which there is little around here.  So things do look different in different areas.  Alas, the ADS-B receiver module I've added to SoftRF does not receive Mode-C transponders.  It does receive Mode-S transponders.  It is not clear to me whether there is a significant number of aircraft with Mode-S transponders (without ADS-B-out) in the US.  There certainly are in Europe, where Mode-C was phased out years ago.

[Andy Blackburn]

It’s actually a tiny population from the perspective of a developer who sells worldwide because the rest of the world is standardized on 1090ES. The whole UAT thing only exists in the US.

Also, if you take the population of US glider pilots who don’t fly XC and just fly within sight of their local airport I’d wager the percent who are also interested in having a gliding flight computer and also are turned off by the fact that it won’t display UAT targets except via ADS-R - because of concerns about ADS-B ground station range - is pretty small (whew, that’s a lot of caveats). All airliners and 4 out of 5 (and rising) GA aircraft are 1090ES equipped. I also think it’s a bit problematic to start equipping the US fleet of gliders with UAT instead of Flarm. It would be preferable to standardize on 1090ES Out plus Flarm for maximum interoperability.

Would it have been better if the FAA had just mandated 1090ES instead of this kludgy dual-band strategy? Yes, but they didn’t. Would it be better if all aircraft in the US were equipped with dual-band ADS-B In instead of relying on ADS-R? Operationally yes, but in terms of cost probably not. Less that 1% of GA aircraft have dual-band receivers.  So now the US is an outlier and it’s going to be challenging to get the gliding equipment vendors to support all the US quirks in an already niche aviation market. 

It took a decade to get ADS-R added to PowerFlarm, so I’m trying to be realistic about looking at this from the developer’s perspective. Nothing in gliding communicates using GDL 90. It seems like an uphill slog with each of the instrument makers. I had something working through Stratux for a couple of years and I think only a handful of people used it. That’s not a great market signal. 

It would be great if more glider pilots in the US logged and uploaded their flights to online platforms like WeGlide - regardless of whether they go on epic XC flights. Navigator is a great tool for doing that.

Andy

On Feb 10, 2025, at 6:28 AM, Paul Remde <pa...@remde.us> wrote:

Hi Dan,

To view this discussion visit https://groups.google.com/d/msgid/naviter-gliding-discussion-group/0ccf6397-1add-4db8-b247-5f70cec58e0fn%40googlegroups.com.

[Andy Blackburn]

The difficulty with the SoftRF device is it doesn’t include the full Flarm feature set and it’s a bit unclear what it does support or how it interoperates with Flarm since it’s reverse-engineered from the Flarm spec which doesn’t disclose all the Flarm collision prediction functionality, which is pretty extensive.

AFAIK SoftRF doesn’t do collision prediction or collision warning at all. Nor does ADS-B. They are traffic awareness/proximity technologies. So if you just do GA-type flying that’s fine but gliders tend to congregate where the thermals are. My understanding is only Flarm does path prediction (such as for turning flight in a thermal) and collision warning. I find that incredibly useful.  My understanding of the warnings that the GA displays perform are for anything getting within an X mile bubble. That’s not as useful for gliders.

So caveat emptor. 

If you don’t carry ADS-B Out you will only get sporadic ADS-R transmissions requested from other nearby 1090ES equipped aircraft. Not great.

Also, surprisingly to me, only a little more than 50% of US GA aircraft have ADS-B Out, though I’d wager if you weight it by flight hours it’s much higher as well as anywhere near a major airport. I figured it would be higher. So if you fly out of a remote GA airport see and avoid could be your primary line of defense.

Andy

On Feb 10, 2025, at 8:32 AM, moshe....@gmail.com wrote:



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[moshe....@gmail.com]

"Less that 1% of GA aircraft have dual-band [ADS-B] receivers."

- Andy, do you have data to back that statement?  My impression is that ADS-B receivers are now common in GA aircraft, even in those that do not have ADS-B-out, even in some with no electrical system (Cubs and Champs).  The reason is: Such receivers are relatively cheap (under $500, can even do it for $200).  And the vast majority of these receivers are dual-band, because that makes them more useful and the extra cost is minimal.

"4 out of 5 (and rising) GA aircraft are 1090ES equipped"

- I wish, then I could see them via my FLARM.  But not so.  Maybe you fly in airspace that makes ADS-B-out pretty much a requirement, but around here (Northern Vermont and New Hampshire) it is very different.

[moshe....@gmail.com]

Andy: please look at the source code and documentation of my branch of SoftRF before making such statements about it.  SoftRF offers 3 types of collision predictions, the two original ones based on proximity and on straight-line paths (as you say, not useful for gliders), and a third one I developed which does predict the paths of circling aircraft.  It sends collision warnings (in standard NMEA sentences like FLARM uses) to attached devices.  And it also beeps, like a Portable PowerFLARM does.  And it also transmits its own position, movement, and turn rate just like FLARM does, so FLARMs that receive its transmissions can use their collision prediction algorithm on that.

[Dan Kvinge]

https://www.easa.europa.eu/en/research-projects/i-conspicuity-interoperability-electronic-conspicuity-systems-general-aviation#group-downloads

If anyone wants to know what is happening NOW, in Europe, this is a great link to the the Euro Aviation Safety Authority report from June 2024.   It's 35 pages but full of interesting hints of what is to come...someday.   Europe and ROW is way ahead of USA in "electronic conspicuity"  (SkyEcho, OGN, Flarm, SafeSky, and many more).    Interesting that the USA low-power UAT approach is looking better as 1090ES gets busier.   Most importantly is to get everyone on board, and share the info so everyone can see it.     And it won't just be FLARM or ADSB.

Thank you Moshe, for your impressive work with SoftRF!   I'm bummed I can get anyone interested in doing it with me and it seems overwhelming to tackle on my own.   I just want to buy something for under $1000.

Dan

[Andy Blackburn]

Here is the FAA data for 2025 for all GA, 1090ES, UAT and Dual Band equippage.

1-Jan-25

169,116

129,504

38,329

1,289

You can see UAT via ADS-R. If you are saying you want to be able to see other aircraft than 1090ES but you don’t want to carry the equipment to do it than I’m not sure what to tell you. It’s the situation we finds ourselves in that European instrument makers for gliders don’t see enough of a market to make a dual-band Flarm. You could probably do a Fork on Stratux to make a device to do it yourself if you can code.

I’m not saying it wouldn’t be useful. I’m just saying if you really want it you’re going to have to do it yourself. I tried and got no interest.

Also, while UAT is 20% of GA ADS-B Out installs and 10% of GA aircraft the bigger issue is 50% of GA aircraft have no ADS-B Out (according to the FAA) and they are all flying in the areas you describe outside of Class A,B,C so your best shot at seeing their position is TIS-B which also requires ADS-B Out. Yeah you won’t see them ridge soaring, but GA don’t do a lot of ridge soaring. Flarm also has PCAS for transponder only aircraft but PCAS sucks.

Andy

To view this discussion visit https://groups.google.com/d/msgid/naviter-gliding-discussion-group/ceb1e967-5ec5-4a09-a3d4-9f398297b1a3n%40googlegroups.com.

[Andy Blackburn]

Moshe,

Impressive work. I hadn’t kept up with the latest developments.

How much interoperability testing have you done?Are the path predictions of SoftRF and Flarm nearly identical? Do they alarm the same way. Will an aircraft with a Flarm and another aircraft with Soft RF both alarm (and not alarm) with identical behavior?

These are important safety issues as you don’t want asymmetry in the alarming, it could cause all sorts of problems with pilots reacting in ways that make the problem worse instead of better. These sorts of split-second moments to avoid another aircraft are difficult under the best of circumstances.

I’m sure you’re thought about it. Did the Flarm guys give you an operating spec to work from?

Also how did you get around the FCC licensing? That’s the big expense item that keeps more of these products from being developed.

Again, impressive that you’ve done so much with it.

Andy

Sent from my iPhone

On Feb 10, 2025, at 9:55 AM, moshe....@gmail.com wrote:

Andy: please look at the source code and documentation of my branch of SoftRF before making such statements about it.  SoftRF offers 3 types of collision predictions, the two original ones based on proximity and on straight-line paths (as you say, not useful for gliders), and a third one I developed which does predict the paths of circling aircraft.  It sends collision warnings (in standard NMEA sentences like FLARM uses) to attached devices.  And it also beeps, like a Portable PowerFLARM does.  And it also transmits its own position, movement, and turn rate just like FLARM does, so FLARMs that receive its transmissions can use their collision prediction algorithm on that.

To view this discussion visit https://groups.google.com/d/msgid/naviter-gliding-discussion-group/4366dc96-29d4-4a59-b4aa-723cf6b363b5n%40googlegroups.com.

[moshe....@gmail.com]

Thanks Andy.  No, FLARM have not disclosed their secret recipe to me (nor anybody else).  And FLARMs do not output the predicted paths, only the current position of the other aircraft and an alarm level (0 to 3, based on time-to-collision).  So all we can do is to try and achieve the same goals of collision prediction, based on the same basic data in the transmissions.

The algorithms being what they are, even two FLARMs do not issue alarms about each other in a symmetrical way.  I had an incident in my glider (equipped with a Portable PowerFLARM) while thermalling, when I suddenly got the highest-level alarm (5 beeps), with no previous alarms.  I could have looked at the gizmos to try and figure out WTF, but of course I looked outside instead, all over, and saw nothing.  The other pilot in the thermal, once we figured out who it was, said that his FLARM did not give him any alarm at the time.  So much for symmetry.

Thankfully, that is an unusual event.  Most of the time we are aware of other traffic nearby well ahead of any possibility of collision, in part thanks to the "electronic conspicuity".  Since FLARMs "see" SoftRF and vice versa, everybody is better off.

Unlike some collision avoidance systems used by airliners, FLARM never tells you what evasive action to take.  If you have to time look at the display it will give you a vague position to look, e.g., 2 O'Clock high.  Better if the device will say that in audible words, so you don't need to look.  Indeed, some devices do that.  XCsoar or Tophat, for example - if you run it on hardware that has audio output (such as a smartphone).  I've added that capability into SoftRF itself (on the "T-Beam" hardware), but you need to add an amplifier and speaker (or connect to your COMM radio's aux input).

In that incident my glider had FLARM feeding data to Tophat running on a device without audio capability.  Some people use SoftRF in conjunction with a display device known as "SkyView", and it offers voice warnings.  Alas the original SkyView software was ill suited for gliders (no subsequent voice warnings for same aircraft after the initial advisory), so I changed that software too, although I don't use it myself.  But, do not confuse SoftRF itself with the display devices, just like FLARM is separate from whatever it feeds data into (FLARMview, Oudie, etc).

BTW I'm not selling anything, I'm just volunteering time into developing ideas which get embedded into open source code.

[moshe....@gmail.com]

Looking at that linked page, it seems that 169,116 is the total of all "equipped" civil aircraft.  Another section there mentions 111,398 as the number of "equipped" fixed-wing GA aircraft.  Google tells me that "As of August 2024, there were more than 167,000 fixed-wing general aviation aircraft in the United States.".  So that leaves about 56,000 (33%) un-equipped.

The table that lists the numbers you posted, with 1289 "dual", seems to mean that 1289 aircraft have both 1090 and UAT output?  The numbers in the last 3 columns add up to the first number (well, off by 6...).  For the FAA, "equipped" means ADS-B *out*.  Receiving ADS-B is completely optional, even in Class A/B/C, and usually being equipped with a receiver is not known to the FAA. If you get a Stratux device and carry it in your Cub, the FAA doesn't know that.  Alas, the pilots in those GA aircraft with (usually dual-band) ADS-B receivers think they are safe since they can "see" all the ADS-B traffic - but they don't "see" each other!

What I wish the SSA would lobby the FAA for in this context is:

* Explicitly allow using UAT978 *out* without also needing a transponder.  E.g., the TailBeacon which some people have figured out how to use in that way, but the FAA frowned on that.  They don't need to approve UAT-only for entry into Class A/B/C, just allow that elsewhere.  Having to add the transponder triples the cost (and the power consumption).  Hence the 56,000 un-equipped aircraft.  The perfect is the enemy of the good.

* Allow low-power ADS-B out (on either frequency).  E.g., the SkyEcho, which is allowed in the UK.  Again, they don't need to approve that for entry into Class A/B/C, just allow that elsewhere. They still seem stuck in the old ground-based ATC perspective, while this new tech allows peer-to-peer visibility, and little transmitted power is needed for that.  (FLARM transmits at about 1/8000 of the power of a transponder.)

[moshe....@gmail.com]

Also note: ADS-R transmissions happen "by request".  The request comes in the form of an ADS-B-out device configured to send some capability info bits saying "I can receive on frequency A but not on frequency B" where A and B can be 1090 or 978.  There are two reasons why an ADS-B-out device would NOT be configured that way:

* the aircraft has only ADS-B out and no ADS-B receiver at all, or

* the aircraft has a single-frequency receiver.

For example, if your glider has a transponder transmitting ADS-B on 1090, and also a FLARM receiving ADS-B on 1090, then your transponder should be configured to say "I can receive 1090 but can't receive 978, please send UAT978 traffic data via ADS-R".

But FLARM is an unusual ADS-B receiver.  Stratux is usually offered in a dual-band version, as all it takes is a second SDR stick which costs about $30.  The fact that ADS-R transmissions are fairly rare hints that most aircraft that do have a receiver have a dual-band receiver.  I live (but not fly) within a Class C airport area, and in hours of capturing received ADS-B data on 1090 (to learn what's happening there, see https://github.com/moshe-braner/dump5892 ) detected very few ADS-R transmissions.  It also seemed to detect almost no aircraft with a Mode S * transponder but without ADS-B 1090ES output (which happens via a Mode S transponder).  I'd like to know whether that is the case elsewhere in the USA.  (* Not Mode C transponders, those are invisible the ADS-B receiver module I am using.)

[Andy Blackburn]

I watched a lot of traffic (and recorded a lot of traffic) - both working on ADS-R for Flarm and on the Stratux project. I saw a ton of traffic that would migrate between 1090ES and UAT, so that had to be ADS-R. Maybe more people are buying dual/ band receivers. 

I think the simple thing would be to migrate everything to 1090ES like the rest of the world. The Dual Band strategy makes everything 50 times more complicated. I think what the FAA was trying to accomplish was not retiring Mode C transponders on the theory that people are price sensitive, but if people are buying dual band radios that kind of flies in the face of that. IIRC Mode C eats up a lot of bandwidth so then you need 978 so 1090 doesn’t get congested and then you need ground-based rebroadcast and you build the ziggurat to FAA bureaucratic thinking. 

But we are where we are.

It would be weird if people with a Mode S transponder were equipping with UAT. That’s two transmitters. That also contradicts the FAA theory that the market won’t spend money. Did they do it to get FIS-B?

It’s a mess and I wish UAT would just die. It’s slowly losing share. Presumably as the GA fleet turns over people just get a Mode S transponder and don’t screw around, but that’s going to take forever.

A.

Sent from my iPhone

On Feb 11, 2025, at 6:32 AM, moshe....@gmail.com wrote:



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[moshe....@gmail.com]

We're still confusing transmitters and receivers here.  Those are separate devices.  Yes, transmitting on both 1090ES and 978UAT is a weird thing to bother to do.  Only about 1% of the aircraft in that FAA report are supposedly doing that.  So it's not a big issue.  And for all we know it may be an error in the analysis behind that report.  E.g., if somebody replaced one type of transmitter with another in their aircraft, does the FAA keep the old info and list that aircraft as "dual"?  If some do transmit on both, it is certainly NOT "to get FIS-B", since we're talking transmitters!

But back to receivers, those are (0) separate unrelated boxes, (1) not required, and (2) not (necessarily) certified, and therefore CHEAP.  The "out" part costs $thousands, the "in" part $hundreds, whether single or dual frequency.  Why do people choose a dual-frequency *receiver*?  Because it is a cheap upgrade ($tens), and then they see all the traffic directly (ADS-R not required), and they also get other (FIS-B) info on 978 (weather, notams...) - for free.

Yes "The Dual Band strategy makes everything 50 times more complicated."  It's a mess.  But, as you said, they can't have everybody migrate to 1090ES unless and until they ban Mode C transponders, which are clogging up the 1090 frequency.  (Because they respond to all ATC radar queries, while Mode S responds individually when asked.)  The congestion on 1090 (in busy airspace areas) is why they want some traffic to stay on 978UAT and why ADS-R only happens by request.

"I wish UAT would just die. It’s slowly losing share."

- I've heard rumors that UAT share of new installations is going up not down, that some holdouts who didn't install ADS-B out, and only have a Mode-C transponder, more recently took advantage of the new more-affordable UAT hardware now available, such as the TailBeacon.  (Which I wish we could use in a glider *without* a transponder.)  But, the FAA report you linked to does show the UAT count slowly decreasing (negating my conjecture that conversions got double-counted in that report?).  So maybe the rumors I've heard are anecdotal and incorrect in the big picture.

I learned from the documents Dan linked to above that in Europe they actually want to introduce UAT - not for traffic, but for the other info (weather etc) that can be broadcast from the ground.  Since the dual-band *receivers* are cheap.