ADS-B Traffic "Ghost" Alerts

[Suzanne C.]

Hello team, I am using the latest version of Avare on Galaxy tab, and ADS-B via ASTROLINK from Levil Corporation. I seem to be getting false positives (ghost) alerts, usually from the 6 o'clock position!

At low altitude (900ft), I've received "traffic 6 o'clock low" and there was absolutely NO ONE below me over the water. I've also received "traffic 6 o'clock closing" when I was in a turn.

I've attached my settings from the audible alerts tab.  FYI the GPS source IS set for the Astrolink. What am I missing?  Thank you.

[Jeffrey Ross]

This is probably an issue with the your ADS-B in device (Astrolink), make sure your device knows your ICAO address so it filters it out from the data stream.  Also you must be ADS-B out equipped and NOT in anonymous mode otherwise you will not be able to pick out yourself from the datastream.

You can also try inputting your ICAO address into Avare under settings -> Pilot and Aircraft -> Aircraft ICAO Code  but I believe the problem is what I outlined above.

Jeff

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[Suzanne C.]

I'm not able to get into the settings of the Astro.

I thought the section "Pilot and Aircraft" in Avare was related to Flight Plan Filing + Glide + Emergency Checklist, so I didn't see that connection, but I will input my ICAO Hex code and see if that makes a difference.  Yes, I am ADS-B out equipped and not anon. As a matter of fact, I do see my aircraft ID in Avare.  Thank you for the suggestion.

[Suzanne C.]

Greetings team. Following the feedback I received previously, I added the aircraft ID to the Pilot and Aircraft section in Avare as well as the ICAO Hex code. 

Today, I finally got a break in the weather and went aloft. I observed precip and traffic on the screen...including my aircraft, but still received ghost alerts "traffic 6 o-clock" or "traffic 6 o-clock low".  Is there anything else that I can do eliminate the ghosting?  Thank you

PS: I also want to add that I had installed their AHRS Utility v7.1 and I see that the aircraft callsign is in the device because it appears when I power up the utility on an iPAD (which I do not use in flight).  My setup is pretty simple... AstroLINK --> Avare.

[Jeffrey Ross]

Your ADS-B in device needs to filter out your aircraft from the data stream, this is not an Avare issue.

Jeff

Sent from my cell phone 

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[Simon Roberts]

I'm aware that my Stratux is capable of this filtering, but... Does the aircraft hex code get sent to Avare? If it does, would it be possible to add the filter? And if it is, might it be possible to add a list of the hex ids to the configuration screens with a radio button to select one for filtering? 

It's perhaps obvious why I'd like a list--I don't currently own and airplane, and therefore fly many different ships, either from clubs or rentals. Having to update the code every time... Well, it doesn't happen :) However, if one could choose from a list (preferably including the aircraft N number for easy reference) that would be much easier to use.

As to why I ask if Avare has the information to do it, well, that's the software I'm connecting to, and actually having to make the separate connection to my ADSB receiver, reconfigure that, and then be ready to launch into Avare, is clearly less convenient. (The fact of having to start the extra software, rather than any implied but unintended observation about startup order).

If the code isn't there, then clearly nothing can be done. And it's just a WIBNIF, obviously.

Cheers,

Simon

[Jeffrey Ross]

No, the "in device" does not tag "own ship" which is why it needs to be filtered out.

I'm going to go out on a limb here to guess as to the reasoning, when the system was designed I'm sure the FAA didn't envision all these portable systems being moved from plane to plane, they figured the in device would be a permanently mounted device which would allow the device to filter out the own ship from the data stream.

Fast forward many years later and you have the world of cheap portable ADS-B in receivers made out of Raspberry Pi computers that before the pandemic cost <$150 to put together (good luck finding a Raspberry Pi for the MSRP of ~$50 now) which I don't think the FAA envisioned when the spec was laid out.

The reason Avare asks for the ICAO code and N-number in the preference screens is for filing flight plans, also I believe ADSB Receiver Pro (which is a 3rd party app) that integrates with Avare may use that to filter out own ship, keep in mind ADSB plugs a SDR into the USB port of the tablet and doesn't use an external receiver.  I can't comment on ADSB Receiver Pro as I don't use it except for once several years ago as a test.

How hard would it be to add the code to have Avare filter out your own ship?  I don't think it would be impossible, and maybe a programmer would be willing to submit code to do that.  The code base is available to download and submit changes on GitHub.

Jeff

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[Shane Lenagh]

This has me considering adding a new feature in the next version where it will (optionally, off by default) audibly call out the full callsign ("November one two tree fower fife")--as I already have the full phonetic alphabet and numbers 0 through 9 in the audio library it is using. Some people might actually like that in some cases, and at the very least it would help debug issues like this (to see who the real "ghost" culprit is).

Avare already has code to filter out ownship from traffic based on those configuration items (https://github.com/apps4av/avare/blob/0f9924091a58c71546a559b9743215d0235a7f75/app/src/main/java/com/ds/avare/adsb/TrafficCache.java#L102) , and the audible alert code is downstream of this. That is why this one really has me stumped, as I agree with you Jeff, it seems like ownship is being reported as traffic here.

Shane

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[Shane Lenagh]

How do you set your callsign/hex code in the AstroLink?  Given it is a portable device (like a Stratus/Stratux), and given the way ADSB works (per Jeff's description), I would think there would be a way to do that.  Yet I can't find any mention of it in their (very short) manual:

https://secureservercdn.net/104.238.69.81/3g5.095.myftpupload.com/wp-content/uploads/2020/11/Astro_Link_Manual.pdf

Shane

[Suzanne C.]

It seems the only way is via the AHRS Utility once connected to the Astrolink for that and other parameters...

[Shane Lenagh]

Ok, that makes sense.  I didn't see it in the manual for the device, but I do see it in the AHRS software manual here: https://secureservercdn.net/104.238.69.81/3g5.095.myftpupload.com/wp-content/uploads/2020/11/AHRS-Utility-Manual-IOS.pdf

Assuming that matches what you put into Avare, I would think it would be differentiating ownship and traffic correctly, if that is what is being reported to Avare.

Shane

[Shane Lenagh]

Another way we might be able to troubleshoot this with the current version is you could use the "Save" feature on the Avare IO tab to save the ADSB data that you are getting from Astrolink to a file on your device, and then we could inspect that to see what is being reported from Astrolink.

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[Rich Klarich]

What is your aircraft's ADS-B OUT source?  A UAT device on 978mhz or a Transponder Mode S/ES on 1090?

I have a UAT and even with "ownship" suppressed, I used to get a traffic alert on myself until the software of my EFIS got updated-   it would happen as your out signals and transponder were first processed at the FAA sites.  I don't think it happens on the 1090-out transponders and it got WAY better with software tweaks on the 978 UAT side.

IF your ownship is set in the software of your ADSB-IN devices, this is my bet.

[Suzanne C.]

ADS-B OUT is via "ES" XPDR

 'ownship' is configured in the ADS-B IN device...at least as verified from the AJRS utility for iThing.

GPS position is sent to Avare and I see traffic +  weather.

[Roger R]

Mine is a hopefully a less complex question and situation. I have just a StratuX in. No out. No ADSB type transponder, just mode C. I get ghost returns on my aircraft too on my tablet. I have read all the postings here and they are way more involved and complex than my situation and I really don't understand the specifics. In any case in my specific situation how can I eliminate the ghost returns. Thanks 

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[Jeffrey Ross]

Roger,

In your situation you cannot eliminate the ghost returns.  Each target that you see on the screen comes with various information two of which are the ICAO and FlightID fields which is how the ADS-B in receiver identifies itself.  In your situation your "target" is being transmitted from the ground station as a simple mode C return which has nothing more than the pressure altitude and calculated position, direction and speed, there is nothing to tag the target as yourself.

I don't think there is any reliable way to identify yourself from the ground station uplink to eliminate the ghost return.  This might also explain why users with UAT out in combination with a mode C transponder may get ghosting, just a guess but maybe the ground station is advertising the mode C target in addition to the UAT target should the ground station not see the UAT target?

Jeff

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[John Schreiber]

Roger, ADS-B out adds the aircraft ID to the "packet". Without that information, you will see your primary transponder output in the data received from the ground based transmitter, but it will be an anonymous return and can't be filtered out. Also, know that unless there is another ADS-B out aircraft nearby to trigger the ground based transmitter, you may not get complete traffic information. ( there are other reasons as well. 

Suzanne, have you pulled a PAPR report to see if all your data is being transmitted correctly? Does your transponder allow anonymous mode? 

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[Jeffrey Ross]

Rodger, good idea I didn't think of suggesting pulling of the PAPR report - https://adsbperformance.faa.gov/PAPRRequest.aspx  you make sure your unit is programmed properly and is reliably being received by ground stations.

Also as an FYI 1090ES does not allow the use of an anonymous mode although the FAA has some sort of "rolling" ICAO address available for 1090ES users if they meet certain conditions, see - https://www.faa.gov/air_traffic/technology/equipadsb/privacy but it isn't as good as anonymous mode, but if you are UAT equipped you can use anonymous mode when squawking 1200 and not using ATC services.

Jeff

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[John Schreiber]

Looking at Jeff's reply, I remembered something related to setting up ADS-B out transmitters. One of the boxes asks for the type of ADS-B in, 1090 or UAT, and usually we would just choose both. 

From AC-90-114B, 

2.3.1 ADS-R. Because the ADS-B system operates on two separate frequencies (1090 MHz and 978 MHz), there is a need to translate, reformat, and rebroadcast the information from each frequency to enable aircraft receiving on the other frequency to process and use the other’s information. This process is referred to as ADS-R and occurs within an ADS-B ground station. An aircraft or vehicle that is ADS-B Out and is receiving ADS-R service is known as an ADS-R client. An ADS-B-equipped aircraft or vehicle on the opposite link of the ADS-R client that has its messages translated and transmitted by the ground system is known as an ADS-R target. See paragraph 2.3.5 for ADS-R client qualification criteria. Note: Aircraft operating on the same ADS-B frequency exchange information directly and do not require ADS-R translation. Aircraft with ADS-B In capability on both UAT and 1090ES do not require ADS-R service.

I wonder if changing this setting (in the transponder) could help with the ghosting effect? 

Obviously the correct ICAO address needs to be transmitted, and filtered in both boxes.

[Suzanne C.]

You make some Interesting points (ref: frequencies) as possible reason(s) for "ghosting". 

To the previous poster's point about the PAPR report, it was requested, aircraft is definitely broadcasting ADS-B on1090MHz.

[Roger R]

Thanks Jeff and John. I don't  see the ghosting all the time. It may have something to do with another airplane and or ground station transmit as you suggest. There is no identifier with it as also suggested. I'll 1) just live with it; and 2) pass your msgs on to a far more computer literate ADSB user friend of mine. If I know it is a ghost then ok...it is when it pops up suddenly that cases a little excitement. Regards.

[Suzanne C.]

In the IO tab, I see the [SAVE] button, and a bunch of data cycling through the lower part of the screen once its connected to the receiver. When I tap the button, it then changes to [SAVING[.   QQ... what is the procedure/process to actually save content into the out.bin file or close it out? The only out.bin file I see out there was last updated in September...

[Steve Voelker]

The same thing happened to me. I switched to Bubble.org and they updated okay.

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[Suzanne C.]

Update...I am definitely the ghost in the machine!

I received traffic alerts "3 seconds and closing...2 seconds and closing". There was nothing that close to me. I received those alerts/chirps in a turn. 

Thanks for the feedback and suggestions.

[Rich Klarich]

Avare Menu, Preference, Pilot and Aircraft, Aircraft ICAO code- is this set for your hexidecimal?

Does your "OUT" tell the FAA that you can receive ADSB-IN on 978 UAT and 1090ES if that matches your IN device?

If a Stratux, via browser 192.168.10.1 usually, is menu, settings, ownship also filled in for the hexidecimal?

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[Rich Klarich]

Levil Astrolink- missed that- their pdf manual does not state how to filter ownship, but they have an app, check there for ownship hexidecimal input.

On Mon, Oct 24, 2022, 13:01 Suzanne C. <sancollinst...@gmail.com> wrote:

Hello team, I am using the latest version of Avare on Galaxy tab, and ADS-B via ASTROLINK from Levil Corporation. I seem to be getting false positives (ghost) alerts, usually from the 6 o'clock position!

At low altitude (900ft), I've received "traffic 6 o'clock low" and there was absolutely NO ONE below me over the water. I've also received "traffic 6 o'clock closing" when I was in a turn.

I've attached my settings from the audible alerts tab.  FYI the GPS source IS set for the Astrolink. What am I missing?  Thank you.

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[Shane Lenagh]

Any chance you (or anyone else having this issue) could record your ADSB input on the IO tab (with the "Save" button) during a flight when this happens and share it with one of us developers? It sounds like you were trying to do that, but maybe just couldn't find where the file saved. 

I have a theory why Avare's attempt to catch this case isn't working, but I would need to see the data to confirm it.

Shane

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[Shane Lenagh]

I took another look a the AHRS software manual that Suzanne mentioned she is using to config the Astrolink, and I see only a place to set the callsign--not the hex code/ICAO address:

https://secureservercdn.net/104.238.69.81/3g5.095.myftpupload.com/wp-content/uploads/2020/11/AHRS-Utility-Manual-IOS.pdf

Well, this is somewhat of a bummer, as Avare (currently) doesn't use the callsign/N-number in its traffic filtering compare to weed own ownships that get sent as a traffic, only the ICAO address:

https://github.com/apps4av/avare/blob/0f9924091a58c71546a559b9743215d0235a7f75/app/src/main/java/com/ds/avare/adsb/TrafficCache.java#L102

Certainly ICAO address is the more "stable/reliable" indicator of the craft identity (callsign could change per flight, and some send N-number and some the per-flight callsign, of course), so I get why it was done that way--and if Astrolink/whatever was sending the same address for this app that is in the Avare preferences screen this line should indeed filter it out.  But maybe having Avare check the callsign/n-number as a secondary filter possibility would be beneficial to try to catch cases where things might slip through the cracks with some of these portable units or the "puck report" scenarios being described.  Such a change would be easy to make, but is it advisable in all cases?  Not sure.  I can say that I tested such a change locally (changed my Avare "N-number" in the preferences to one of my existing simulated traffic targets, and it disappeared with the change below).  Thoughts?

Here is one possible implementation of that change--very small (more nerd stuff, I know):

Shane

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[Apps4av Support]

It will not fix the issue because tail number is not always present. But it will improve.

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[Diane Cook]

Hi all, we just got our LSA out of extended (9 month long) maintenance, and it’s flying again.  I love all the improvements Avare has over last 9 months, but now we are suffering from the “Ghost Image” that Suzanne describes above.  We have an EchoUAT adsb (in and out) which was playing nicely with Avare before our hiatus, no ghosts, now we have a little unidentified bogey about 300 ft above us, and just behind traveling at our speed.…scary!   I turned on call signs and nothing appeared, and recalled this stream from a month ago…and thought I best find out to solve the problem.

I’ve read thru the above stream, and think that  I simply need to be sure the EchoUAT has our icao number and N number and is not operating anonymously, in its set up. Is there anything in the Avare setup I need to change?   Have I missed anything that would eliminate the ghost?

I appreciate your help.  Will be sending a year end donation shortly! …the crew has had a busy year! Good job!!

[Apps4av Support]

Hi Diane

Thank you ! 

Did you set the N number in the preferences ? If you can send the recorded ads file we can check what's in it that does not match the N number or the icao number.

Thanks

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[Diane Cook]

Both icao number and n number are in Avare preferences unchanged from before we had the long flying hiatus. Though on one of the 3 devises we use I noticed our n number had a one digit error, which I corrected.  My hubby(the family pilot, I’m the techie) confirmed the icao number is correct.  

Can you tell me how to record an ads file? (I reread Shane’s note to Suzanne above re recording Adsb by pushing save on the IO screen— maybe it’s that simple?), then where to look for the file on my phone/tablet?, and, finally how to send to you?  Do I record when I see the ghost, or anytime during flight?  Do you want a file from each devise?

Weather is wintry here in Az, so it may be awhile til we get airborne again.

[Apps4av Support]

Just one device that shows the issue and yes, using the tools menu, record the file. 

You can export the file using the tools menu export, attach to email, then send.

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