ADSB visibility with non certified GPS

On Thursday, September 28, 2017 at 9:01:37 PM UTC-7, Darryl Ramm wrote:
On Thursday, September 28, 2017 at 6:53:44 PM UTC-7, Tom BravoMike wrote:
/snip/
3. Why do so many sources say: You fly above 18,000 ft? Go for 1090. You fly below? Go for 978 ? See in that respect e.g.

https://www.garmin.com/en-US/blog/av...on-is-for-you/

but disregard the specific equipment suggested.
/snip/

Tom

Sounds like you have a great handle on stuff here to help make the right decisions for you.

I would not give too much weight too much to the UAT argument in that blog. it's from several years ago, and suspect it is coming at a time where there actually started to be more 1090ES out installs in GA. Garmin might have had a sales reason around that time to mention UAT product upgrades (on the GLD88) and also may have in part just been echoing the FAAs vision for how ADS-B dual-link was going to be deployed. Today below 18,000' I think it is a good mix of UAT and 1090ES.

Some comments in the strange gymnastics behind dual-link in the USA: Originally the FAA has a view that UAT would be used for all lower altitude aircraft (then below FL240, later lowered to 18,000'), driven by concerns about 1090 MHz congestion, and likely expected costs of Mode S transponders, and likely a desire to create a user base of UAT to make FIS-B successful (and have FIS-B successful to encourage UAT adoption..). And organizations like AOPA and EAA liked the idea of keeping Mode C transponders so liked the idea of UAT, and so on.

... but much of it is probably not true, Mode S transponders are not hugely expensive (for what they do), the rest of the word ignored UAT and went 1090ES only, so economies of there helped lower prices and will continue to, lots of folks "cheated" and got free FIS-B with portable devices without playing in ADS-B proper, ADS-B Out for many install its easier to upgrade older transponders with plug in replacements (and use existing antenna and wiring etc.) , or do a Mode S transponder firmware upgrade , etc., etc. It's a very complex system and I don't think played out as envisioned early on, really complex systems rarely do.

It seems that lots of GA folks are installing lots of different ADS-B Out stuff, in the mid-high end GA market I see people going with 1090ES Out and Dual-Link In. And not just for people who might fly in class A airspace. Much of that is driven by easy upgrades/add on to their transponders

As for PowerFLARM adoption, glider ports and operations that I know have strong adoption, most people flying cross country have it. The thing that matters is where you fly, if PowerFLARM usage is very low (and not likely to increase) then its a non-issue.

I'm not sure there us somebody else able to develop the software equivalent for ADS-B to what makes FLARM useful between gliders, usable at all in thermals etc. I've seen the issues with PowerFLARM, it was very frustrating, but I think we are on a stable/usable system now.

BTW I was talking with the ADS-B contact at a FSDO today and he sort of confirmed my feeling. ADS-B Out installs in GA are incredibly busy, shops backed up. Most GA installs there seem to be 1090ES Out, with UAT Out used in lower-end aircraft like flight school 150/152. Stats may be skewed in major metro area/more high-end aircraft?

Looking for the usage split with a dual-link receiver would be interesting.... Andy Blackburn you got any observations for GA?

On Friday, September 29, 2017 at 4:45:24 PM UTC-7, Darryl Ramm wrote:

Looking for the usage split with a dual-link receiver would be interesting... Andy Blackburn you got any observations for GA?

My observations are anecdotal and based on living 15 miles from SFO. I need to take my rig out away from a major airport to where it's mostly GA. With that disclaimer, here's what I saw sitting near the San Carlos, CA airport..

The targets shown on linked screenshots (link below) are from a version of Stratux that shows the type of ADS-B traffic by appending two characters to the beginning of the aircraft ID - e=1090ES, u=UAT for the link frequency; a=ADS-B direct, t=TIS-B, r=ADS-R. The screenshots are from earlier in the summer.

Observations:
1) Most of the ADS-B direct traffic is 1090ES, even for non-airline traffic.. I haven't done a lot of looking up of aircraft IDs to sort out type of aircraft. I'm presuming a bias towards high-end aircraft based on my location..
2) There is some UAT traffic, because something is asking for ADS-R and TIS-B over UAT and it's not me.
3) There seems to still a lot of transponder-only traffic as evidenced by all the TIS-B traffic. I am assuming that if this traffic had an ADS-B direct signal it would take display precedence over TIS-B.
4) A lot of aircraft appear to not have their ADS-B aircraft type set properly as jets seem to pretty regularly show up as pistons. Still trying to figure that one out.
5) Lots of traffic flips between ADS-B direct and ADS-R. I'm assuming this is based on whichever signal is stronger or some de-duplicating logic in Stratux.

https://drive.google.com/open?id=0Bw...Eg5ME8zZmNJWGs

Andy Blackburn
9B

On Saturday, September 30, 2017 at 12:12:11 PM UTC-7, Andy Blackburn wrote:
/snip/
3) There seems to still a lot of transponder-only traffic as evidenced by all the TIS-B traffic. I am assuming that if this traffic had an ADS-B direct signal it would take display precedence over TIS-B.

Yep. The aircraft has UAT or 1090ES Out then you generally won't see TIS-B reports for it as all the client aircraft should have that data satisfied by ASD-B direct or ADS-R. There must be some cases where SSR targets are not deduplicated with Mode C transponders and broadcast anyhow. That should be a pretty low, but I don't know any numbers. I suspect you are really seeing all the folks who have yet to go ASD-B Out at all.

So is it possible that UAT will be abandoned and everybody move to 1090ES? And then the FAA will stop mirroring the info as ADS-R to the UAT frequency? If that happens, will the existing PowerFLARM devices become useless (other than flarm-to-flarm warnings)?

On Saturday, September 30, 2017 at 2:23:52 PM UTC-7, wrote:
So is it possible that UAT will be abandoned and everybody move to 1090ES? And then the FAA will stop mirroring the info as ADS-R to the UAT frequency? If that happens, will the existing PowerFLARM devices become useless (other than flarm-to-flarm warnings)?

UAT won't be abandoned, there is clearly significant use out there. And the FAA/and its' contractors and owners have already invested a huge amount in all this infrastructure. This discussion went off on talking about the relative adoption of 1090ES and UAT vs older assumptions that it would be largely UAT at lower-altitudes, and that is not what appears to be happening. And UAT receiver technology allows FIS-B data display for weather and TFRs etc. which is a nice benefit and nobody will want that taken away.

I don't understand why you think existing PowerFLARM devices are related to UAT. The only ADS-B thing a PowerFLARM can do is receive 190ES In, and only that direct from the 1090ES Out aircraft. They come out of Europe were there is no UAT and are completely incompatible with UAT. If UAT never existed PowerFLARM would be *more* useful in the USA because you would see all ADS-B Out traffic. PowerFLARM does not transmit on UAT, can't see UAT, and can't receive ADS-R relay of UAT traffic (even if you have a suitable ADS-B Out system to cause your glider to become an ADS-R client).

On Saturday, September 30, 2017 at 5:39:42 PM UTC-4, Darryl Ramm wrote:
I don't understand why you think existing PowerFLARM devices are related to UAT. The only ADS-B thing a PowerFLARM can do is receive 190ES In, and only that direct from the 1090ES Out aircraft. They come out of Europe were there is no UAT and are completely incompatible with UAT. If UAT never existed PowerFLARM would be *more* useful in the USA because you would see all ADS-B Out traffic. PowerFLARM does not transmit on UAT, can't see UAT, and can't receive ADS-R relay of UAT traffic (even if you have a suitable ADS-B Out system to cause your glider to become an ADS-R client).

- thanks Darryl. So I had the ADS-B frequency that PowerFLARM uses backwards. So is ADS-R one-way only, relaying 1090ES traffic to UAT and not the other way around? Doesn't that limit the usefulness of UAT for GA aircraft, if it does not make them directly visible to the heavies? Or is there some other reason why PF won't receive ADS-R? (This over-complicated system makes my head hurt.)

On Sunday, October 1, 2017 at 4:09:40 PM UTC-7, wrote:
On Saturday, September 30, 2017 at 5:39:42 PM UTC-4, Darryl Ramm wrote:
I don't understand why you think existing PowerFLARM devices are related to UAT. The only ADS-B thing a PowerFLARM can do is receive 190ES In, and only that direct from the 1090ES Out aircraft. They come out of Europe were there is no UAT and are completely incompatible with UAT. If UAT never existed PowerFLARM would be *more* useful in the USA because you would see all ADS-B Out traffic. PowerFLARM does not transmit on UAT, can't see UAT, and can't receive ADS-R relay of UAT traffic (even if you have a suitable ADS-B Out system to cause your glider to become an ADS-R client).

- thanks Darryl. So I had the ADS-B frequency that PowerFLARM uses backwards. So is ADS-R one-way only, relaying 1090ES traffic to UAT and not the other way around? Doesn't that limit the usefulness of UAT for GA aircraft, if it does not make them directly visible to the heavies? Or is there some other reason why PF won't receive ADS-R? (This over-complicated system makes my head hurt.)

It might help to remember PowerFLARM does 1090ES In (ie. the 1090 MHz transponder reply frequency) because PowerFLARM also uses that same 1090 MHz receiver to provide PCAS detection. (UAT operates on 978 MHz).

ADS-R goes both ways. The ADS-B Out system in an aircraft has "CC" capability code flags that describe if the Aircraft has ADS-B In on UAT or 1090ES (and obviously if neither flag set then no ADS-B In). The FAA ADS-B Ground systems looks at that "client" aircraft and "target" aircraft nearby it (within 15 naut. mile radius +/- 3,500' "hockey puck") and transmits data from the ADS-B link layer it knows the client can't receive to the one it can. If the client has no or both link layers (as many the systems do now) it won't be an ADS-R client at all. A properly configured dual link layer receiver aircraft may still be a TIS-B client (if the target does not have ADS-B Out at all).

ADS-B In systems may not operate fully/as expected unless the ADS-B Out transmitter for that aircraft has the CC flags set correctly. This incorrect setup is especially likely with portable ADS-B In system. Luckily most portable and fixed (GA focused) ADS-B receivers are now dual-link which makes this less of an issue... but you might still not receive TIS-B. Make sure you understand how your setup in your specific aircraft will work.

The actual retransmission data message via ADS-R, is very slightly different than the message it is retransmitting... the FAA system could not work it it was exactly the same. PowerFLARM coming out of Europe was apparently never developed to handle those slightly different USA focused ADS-R messages..

Remember outside of gliders all UAT Out equipped aircraft that are expected to get near an airliner are also going to have a transponder. That transponder is going to always be seen by the airliners TCAS II system. The ultimate magic of a TCAS II RA (resolution advisory) where TCAS directs the pilot (and the pilot must follow) what to do, only ever happens via transponder interrogation. A TCAS II system will fly into a UAT only equipped target with no RA. Airliners may also have 1090ES In and Out and will be ADS-R clients, that can be used to paint traffic on displays etc. It does not drive a TCAS RA. The needs for transponders in areas of busy airliner and fast jet traffic for TCAS compatibility is a very important issue. That ASG29 vs. Hawker 800 middair... yep the Hawker 800 had full TCAS II, glider had its transponder (recently installed but not yet tested/signed off) turned off.....

Andy,

What hardware/software are you running to display the Stratux data stream?

On Saturday, September 30, 2017 at 5:03:10 PM UTC-7, SoaringXCellence wrote:
Andy,

What hardware/software are you running to display the Stratux data stream?

Here's a list of compatible apps.

http://stratux.me

Andy

On 09/30/2017 01:12 PM, Andy Blackburn wrote:

4) A lot of aircraft appear to not have their ADS-B aircraft type set properly as jets seem to pretty regularly show up as pistons. Still trying to figure that one out.


I've been watching 1090ES traffic on a FlightAware (Piaware) receiver
for several years. 60 Miles N of Denver International, so see lots of
jets headed up to Seattle area. I don't ever remember seeing a jet
misidentify as a piston plane on my system.

There used to be some occasional errors, like a heading always showing N
regardless of actual track over the ground, and position reports wildly
bouncing all over the place, but those seem to be cleaned up now.

-Dave