978 UAT ads-b upgrade weirdness

[Indiana_Pilot]

I have had a Freeflight 978 FDL-TX Ads-b out unit for well over a year now.. it has been working great paired with my Stratus 2. I have been wanting a all in one solution. They offered to upgrade me (at a cost of course) to their UAT Transceiver.

It was installed last night and I took it for a test flight.. It seems that the ads-b weather radar "paints" much faster with this unit compared to the stratus..

The bigger difference is I only have single band receive now.. meaning I won't see air to air 1090 ads-b traffic.. not a big deal but does reduce the targets somewhat while on the ground or not in ads-b coverage (in my area under 800' agl.)

I expected to only see other UAT equipped aircraft and then TIS-B traffic afterI climes in range of the ads-b system.. I went for a test flight last night after the install and didn't see any traffic.. not a big deal because the way I am configured now I would only be able to see traffic in my "hockey puck"

The odd thing was is that I did see one target 50 miles away over KIND and it was a tis-b target.. I thought tis-b was only aircraft within 15nm and +/- 3500' ?

Anyone else see tis-b (non ads-b aircraft) that far away?

 

[Clark1961]

If a tower within your range is broadcasting tis-b traffic you will be able to see it depending on your display software settings. Nothing limits the data broadcast to a particular receiver. As an example, on a busy day we will see all traffic around Denver from the Wyoming border to the Palmer Divide because lots of ABS-B outs are calling for tis-b.

 

[Indiana_Pilot]

I understand that but I also was under the impression that I would only see TIS-B traffic that was within the 15nm range of me.. I can see that I should air to air traffic further away..


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[denverpilot]

I understand that but I also was under the impression that I would only see TIS-B traffic that was within the 15nm range of me.. I can see that I should air to air traffic further away..


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That's completely up to the software implementation. The targets are being broadcast by the 978 tower.

Whether your devices decide to spend the extra processing time to deal with figuring out how far away a target is to keep or toss it, or if they just choose to locate all targets received and you see them if you zoom out, is completely up to the developer.*

*Within whatever mandated display specs FAA puts on ADS-B IN devices.

Some display apps and devices even give you the option whether to display far away targets or not, settable by the user.

 

[Clark1961]

I understand that but I also was under the impression that I would only see TIS-B traffic that was within the 15nm range of me.. I can see that I should air to air traffic further away..


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The display software may offer a limit on the range and/or altitude of displayed traffic. Nothing other than line of sight to the ADS-B tower inherently limits the traffic displayed.

 

[Indiana_Pilot]

The display software may offer a limit on the range and/or altitude of displayed traffic. Nothing other than line of sight to the ADS-B tower inherently limits the traffic displayed.

I am not so sure that is true.. for TIS-B targets not air to air targets are tailored to your physical GPS location.. they are supposed to provide only tis-b traffic for your area in a 15nm radius.. (remember all the people without ads-b out being able to receive tis-b traffic but only when in range of ads-b out traffic) ?

 

[Clark1961]

I am not so sure that is true.. for TIS-B targets not air to air targets are tailored to your physical GPS location.. they are supposed to provide only tis-b traffic for your area in a 15nm radius.. (remember all the people without ads-b out being able to receive tis-b traffic but only when in range of ads-b out traffic) ?

You aren't thinking it through. The system was never designed to limit traffic to an individual receiver as you suggest. There is nothing in the spec that says traffic info is limited to a particular receiver. If a tower is sending traffic data and your antenna has line of sight to that tower then you get the data. How many towers can you "see"? How many other aircraft can "see" one or more of the same towers? Get it yet? or do you want to keep arguing?

 

[Axtel4]

It could be that you were seeing traffic from someone else's "Hockey Puck" that overlapped yours. BTW, does your device identify the traffic source by tagging the targets as TS-B, ADS-B, or ADS-R?

 

[Indiana_Pilot]

Yes it does.. and it displayed the aircraft as a TIS-B target.. meaning they only have a mode c and ATC was seeing them on secondary radar. They were over 50 miles away in Indy so I just though it was odd..

As to the other question, I receive multiple towers but I am pretty sure they tag the data to be for your "hockey puck" only.. if not then why would you need to be in range of another ads-b out aircraft.

 

[denverpilot]

Yes it does.. and it displayed the aircraft as a TIS-B target.. meaning they only have a mode c and ATC was seeing them on secondary radar. They were over 50 miles away in Indy so I just though it was odd..

As to the other question, I receive multiple towers but I am pretty sure they tag the data to be for your "hockey puck" only.. if not then why would you need to be in range of another ads-b out aircraft.

They don't AFAIK tag data just for you. Even if they do, your receiver can simply ignore that data field and display whatever it wants to display. The traffic for someone else's hockey puck is as valid as traffic tagged for yours. But I don't think such a tag is even there. This is already what aircraft with IN and no OUT are doing anyway, just displaying whatever comes up. Who cares who it's "tagged" for? Traffic is traffic. Displaying it is the job of the user interface settings on the display.

That's what makes the hockey puck so stupid overall. If it's a SAFETY system you just transmit ALL TRAFFIC in the COVERAGE AREA. You're going to be doing that anyway when everyone is equipped with OUT except in the very rare instance some aircraft with a waiver for OUT is not inside someone else's "puck".

And that's just plain STUPID design work. The ONLY reason to even have a "puck" is to convince folks to buy OUT. The additional ground processing and silly over-engineered ruleset is absolutely moronic for a so-called "safety" system and significantly REDUCES safety. Which makes FAA look utterly stupid when they make marketing claims that ADS-B's primary goal was safety.

They should remove the "puck" processing altogether and just dump it. They only did it so they could cram more IN data for non-traffic data types into the continuous data stream going up on 978, ostensibly to speed up stuff like weather. It's a bandwidth game and a dangerous one.

Traffic should always take priority over weather and other ancillary data services. ALL traffic.

But anyway back to your issue. Your Stratus and the other IN-only device happily relied on traffic reports from any aircraft that were broadcast. You didn't have a "puck" and still saw the traffic. Same deal now that you have OUT.

You see whatever the software developer decided to show you, of any traffic in the data stream coming up from the 978 tower. They can display every target no matter who's "puck" triggered FAA to send it. The receiver doesn't care.

 

[Indiana_Pilot]

I get the whole puck thing and I know it's not traffic just for me but is traffic within the area I am currently at.. I guess I didn't realize that I could see someone else puck 50nm away?? I ahve ads-b out and in for almost 2 years now.. but always only seen tis-b traffic within 15nm of me or so (within my puck) never that far away.. I ahve of course always seen the 1090 and 978 out guys hundreds of miles away when airborne..

 

[Axtel4]

Yes it does.. and it displayed the aircraft as a TIS-B target.. meaning they only have a mode c and ATC was seeing them on secondary radar. They were over 50 miles away in Indy so I just though it was odd..

As to the other question, I receive multiple towers but I am pretty sure they tag the data to be for your "hockey puck" only.. if not then why would you need to be in range of another ads-b out aircraft.

Granted, when a tower sees an ADS-B Out transmission tagged with ADS-B In capability it will broadcast all the traffic within a 30 nmi diameter +/- 3500 ft "Hockey Puck" of the requesting ADS-B Out device. Notice here, the term is "Broadcast" and the ADS-B ground station reply is not addressed to a specific ADS-B In receiver. As such, any aircaft within range of the tower will receive the broadcast of all the TIS-B / ADS-R traffic within the 30 nmi diameter of the "requesting" ADS-B Out transmission.

For example, you are requesting ADS-B traffic data from a ground station. Also, there is an aircaft centered 15 nmi ahead of you and one centered 15 nmi behind you that is also request ADS-B traffic data from the same tower. Since you are in range of the tower, all traffic in a 60 nmi x 30 nmi line will be visible in the broadcast due to the three different requests for ADS-B traffic data. Also, any aircraft within your "Hockey Puck" that is ADS-B Out equipped will also see all the traffic you and the other two aircraft see in the broadcast.

 

[Clark1961]

They don't AFAIK tag data just for you. Even if they do, your receiver can simply ignore that data field and display whatever it wants to display. The traffic for someone else's hockey puck is as valid as traffic tagged for yours. But I don't think such a tag is even there. This is already what aircraft with IN and no OUT are doing anyway, just displaying whatever comes up. Who cares who it's "tagged" for? Traffic is traffic. Displaying it is the job of the user interface settings on the display.

That's what makes the hockey puck so stupid overall. If it's a SAFETY system you just transmit ALL TRAFFIC in the COVERAGE AREA. You're going to be doing that anyway when everyone is equipped with OUT except in the very rare instance some aircraft with a waiver for OUT is not inside someone else's "puck".

And that's just plain STUPID design work. The ONLY reason to even have a "puck" is to convince folks to buy OUT. The additional ground processing and silly over-engineered ruleset is absolutely moronic for a so-called "safety" system and significantly REDUCES safety. Which makes FAA look utterly stupid when they make marketing claims that ADS-B's primary goal was safety.

They should remove the "puck" processing altogether and just dump it. They only did it so they could cram more IN data for non-traffic data types into the continuous data stream going up on 978, ostensibly to speed up stuff like weather. It's a bandwidth game and a dangerous one.

Traffic should always take priority over weather and other ancillary data services. ALL traffic.

But anyway back to your issue. Your Stratus and the other IN-only device happily relied on traffic reports from any aircraft that were broadcast. You didn't have a "puck" and still saw the traffic. Same deal now that you have OUT.

You see whatever the software developer decided to show you, of any traffic in the data stream coming up from the 978 tower. They can display every target no matter who's "puck" triggered FAA to send it. The receiver doesn't care.

http://adsbforgeneralaviation.com/w...SBS-Description-Doc_SRT_47_rev01_20111024.pdf page 45 or so. Nothing ties "in" with "out"

 

[Axtel4]

For FIS-B, no. For traffic it does. DF-17 Type 31Bit 44 (ESI, ES In receiver) and Bit 48 (UT, UAT receiver) Ref. DO-260B.

 

[vontresc]

There are a few things you have to properly configure in your box. The ADS-b out has a bit to tell you on what frequency you can receive actual ADS-b traffic. in your case you have UAT/978 in, but no 1090 in. If this isn't properly set you may not get all the traffic. If you are only single band in the ground stations will retransmit the 1090 on UAT and vice versa (ADS-R). If you are not seeing any 1090 or ADS-r traffic, that is possible not set properly.

 

[Clark1961]

For FIS-B, no. For traffic it does. DF-17 Type 31Bit 44 (ESI, ES In receiver) and Bit 48 (UT, UAT receiver) Ref. DO-260B.

Page 45 of the document I linked. Format is lost. Anyway there is nothing that sez anything about for whom the traffic message is intended.

Table 3-9: Payload Composition of 1090ES TIS-B Messages TIS-B Message Encoding Used TIS-B Message Field MSG Bit # DO-260B Reference All Set to decimal 18 (10010) for all TIS-B Messages DF TYPE 1-5 §2.2.17.2.1 “2” for Fine TIS-B Message with AA=24-bit ICAO address and “5” for Fine TIS-B Message with AA=TISB Service generated 24-bit track ID Control Field (CF) 6-8 §2.2.17.2.2 A 24-bit address; ICAO address or service generated track ID Address Announced (AA) 9-32 §2.2.17.2.3 Algorithm that operates on the first 88 bits of the message Parity / Identity (PI) 89-112 §2.2.3.2.1.7 TIS-B Fine Airborne Position Determined from altitude type and NIC TYPE 33-37 §2.2.3.2.3.1 Set to 00 for all TIS-B Messages Surveillance Status 38-39 §2.2.3.2.3.2 “0” to indicate a 24 bit address Note: This flag is always set to 0 since Mode 3/A code is not allowed to be embedded in the 24-bit address ICAO Mode Flag (IMF) 40 §2.2.17.3.1.2 12 bits of barometric altitude data. Pressure Altitude 41-52 §2.2.3.2.3.4.1 Set to ZERO Reserved 53 - Transmit Function to alternate between “0” = even; “1” = odd. CPR Format 54 §2.2.3.2.3.6 CPR encoded Latitude and Longitude of target position. CPR Latitude 55-71 §2.2.3.2.3.7 CPR Longitude 72-88 §2.2.3.2.3.8 TIS-B Fine Surface Position Determined from altitude type and NIC TYPE 33-37 §2.2.3.2.4.1 Ground Speed of target on surface (Note: the movement field is different in DO-260B) Movement 38-44 §2.2.3.2.4.2 Validity of heading/ground track Heading Status 45 §2.2.3.2.4.3 Ground Track/Heading of target on surface Heading 46-52 §2.2.3.2.4.4 “0” to indicate 24 bit ICAO address ICAO Mode Flag 53 §2.2.17.3.1.2 Transmit Function to alternate between “0” = even; “1” = odd. CPR Format 54 §2.2.3.2.4.6 CPR encoded Latitude and Longitude of target position. Latitude 55-71 §2.2.3.2.4.7 Longitude 72-88 §2.2.3.2.4.8 TIS-B Velocity Set to 19 (10011) for all Velocity Messages TYPE 33-37 §2.2.3.2.6.1.1 Determined based on availability of data on target velocity over ground and whether target is supersonic Subtype 38-40 §2.2.3.2.6.1.2 “0” to indicate 24 bit ICAO address ICAO Mode Flag 41 §2.2.17.3.1.2 TIS-B Service generated NACP value NACP 42-45 §2.2.17.3.4.4 Velocity data on target (Always set to ZEROs for Surface Targets) Subtype 1& 2 E/W Direction 46 §2.2.3.2.6.1.6 E/W Velocity 47-56 §2.2.3.2.6.1.7 N/S Direction 57 §2.2.3.2.6.1.8 N/S Velocity 58-67 §2.2.3.2.6.1.9 All Subtypes Vertical Rate Source (GEO Flag) 68 §2.2.3.2.6.1.10 Vertical Rate Sign 69 §2.2.3.2.6.1.11 Vertical Rate 70-78 §2.2.3.2.6.1.12 Based on position TYPE codes and integrity containment radius for target position NIC Supplement 79 §2.2.17.3.4.3 FAA Surveillance and Broadcast Services Surveillance and Broadcast Services Description Document SRT-047, Rev. 01 – October 24, 2011 Page 46 of 132 TIS-B Message Encoding Used TIS-B Message Field MSG Bit # DO-260B Reference For Messages with GEO Flag = 0 Currently set to “0” (Note: The FAA is processing a Requirements Change Request to set the NACV based on the actual velocity performance of the surveillance source) NACV 80-82 §2.2.3.2.6.1.14 Configured Value (default is “2”) SIL 83-84 Set to decimal 0 (0000) Reserved 85-88 For Messages with GEO Flag = 1 Set to 0 Reserved 80 §2.2.3.2.6.1.15 Based on altitude difference between barometric and geometric sources Diff from Baro. Alt Sign 81 Diff. from Baro. Alt. 82-88

 

[Axtel4]

Page 45 of the document I linked. Format is lost. Anyway there is nothing that sez anything about for whom the traffic message is intended.

Correct, the TIS-B / ADS-R payload is not intended for nor is it addressed to anyone in particular, thus "Broadcast". However, the GBT must receive the ADS-B In equippage bit and the proper NACp/NACv/SIL/SLA Client Status data* from an ADS-B Out emmitter to trigger the payload uplink. The payload will be uplinked via UAT (or ES as provisioned for in the specs) depending on the Bit setting. If the GBT does not see the proper ADS-B In bit and valid Client Status data on DF-17 then it will not broadcast the TIS-B / ADS-R payload.

None of the above applies to the FIS-B payload.

*Reference FAA "Changes to the TIS-B Service beginning in late 2015" Policy Statement dated 31 March 2015 for details.

 

[Clark1961]

Correct, the TIS-B / ADS-R payload is not intended for nor is it addressed to anyone in particular, thus "Broadcast". However, the GBT must receive the ADS-B In equippage bit and the proper NACp/NACv/SIL/SLA Client Status data* from an ADS-B Out emmitter to trigger the payload uplink. The payload will be uplinked via UAT (or ES as provisioned for in the specs) depending on the Bit setting. If the GBT does not see the proper ADS-B In bit and valid Client Status data on DF-17 then it will not broadcast the TIS-B / ADS-R payload.

None of the above applies to the FIS-B payload.

*Reference FAA "Changes to the TIS-B Service beginning in late 2015" Policy Statement dated 31 March 2015 for details.

Yeah, most everyone knows that and that point was not in question here. The OP thought traffic info was specific to a receiver and that is not true.

 

[Indiana_Pilot]

Yeah, most everyone knows that and that point was not in question here. The OP thought traffic info was specific to a receiver and that is not true.

Not specific to receiver but area...


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[Clark1961]

Not specific to receiver but area...


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If by area you mean line of sight with a tower that has received an ADS-B signal from an aircraft with the in bit set then yes, area. As Nate has noted the traffic info can be incomplete which in practice turns out to not help with the bandwidth problem the traffic "puck" was supposed to address. The traffic "puck" is really just a bad idea that wasn't well thought out.

 

[Indiana_Pilot]

No the “hockey puck” area. Tis-b traffic broadcast is targeted to a certain area For a participating aircraft


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[Clark1961]

No the “hockey puck” area. Tis-b traffic broadcast is targeted to a certain area For a participating aircraft


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The broadcast is omni-directional. It is not targeted to an area. It is limited in information which is what Nate and I have said.

 

[Axtel4]

No the “hockey puck” area. Tis-b traffic broadcast is targeted to a certain area For a participating aircraft

As stated above the TIS-B / ADS-R is broadcast omnidirectionally around the Ground Base Tower. However, the data contained within that omnidirectional broadcast is comprised of the data based on the "Hockey Puck" of the requesting ADS-B emmitter. Any ADS-B In aircraft within the service area of the tower will receive the broadcast data triggered by the compliant ADS-B Out emmitter.

Think of the 978 MHz UAT towers this way;

There are three classes of towers; low altitude, medium altitude and high altitude that cover a specific airspace volume with different types of FIS-B data for each tower class. Each tower is designed to cover a specific altitude and service volume around the tower and is limited to a maximum power of 50 dBm. To control the service volume for each tower, the launch angle of the antenna is established for each tower class. To visualize this, place a cone over each type of tower with the point of the cone at the base of the tower and the cone base directly above the antenna. Since each tower class has a max power of 50 dBm, the service volume is controlled by the cone shape (antenna launch angle) with each cone having the same volume. A low altitude tower will have a short fat cone whereas a high altitude tower will have a tall skinny cone. The visualization of the cone placed over the tower helps one understand why a person has to get close to a tower while on the ground to receive a signal and why the coverage distance from the tower increases with altitude.

 

[Indiana_Pilot]

As stated above the TIS-B / ADS-R is broadcast omnidirectionally around the Ground Base Tower. However, the data contained within that omnidirectional broadcast is comprised of the data based on the "Hockey Puck" of the requesting ADS-B emmitter. Any ADS-B In aircraft within the service area of the tower will receive the broadcast data triggered by the compliant ADS-B Out emmitter.

Think of the 978 MHz UAT towers this way;

There are three classes of towers; low altitude, medium altitude and high altitude that cover a specific airspace volume with different types of FIS-B data for each tower class. Each tower is designed to cover a specific altitude and service volume around the tower and is limited to a maximum power of 50 dBm. To control the service volume for each tower, the launch angle of the antenna is established for each tower class. To visualize this, place a cone over each type of tower with the point of the cone at the base of the tower and the cone base directly above the antenna. Since each tower class has a max power of 50 dBm, the service volume is controlled by the cone shape (antenna launch angle) with each cone having the same volume. A low altitude tower will have a short fat cone whereas a high altitude tower will have a tall skinny cone. The visualization of the cone placed over the tower helps one understand why a person has to get close to a tower while on the ground to receive a signal and why the coverage distance from the tower increases with altitude.

Ok now that makes sense so you are saying I can see other hockey traffic.. I guess I assumed I would only see TIS-B traffic for my own hockey puck not others... thanks and sorry for my stupidity that is one thing about ads-b I didn’t know!


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[Axtel4]

Ok now that makes sense so you are saying I can see other hockey traffic.. I guess I assumed I would only see TIS-B traffic for my own hockey puck not others... thanks and sorry for my stupidity that is one thing about ads-b I didn’t know!


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Not to worry. They have done everything they could to make ADS-B confusing and convoluted.