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Two returns for same plane

recapen

Well Known Member
I was out on a long cross country on Sunday.
Multiple times (not every time) during the flight I would see two 'targets' in my ADS-B in display. The two were not exactly overlaid and as I got closer, they superimposed to almost a single 'target'. When I actually made eye contact, there was only one plane.

I have a NavWorx ADS600B 200-0013 (operating under AMOC) UAT using a GNS 430W as the position source, SL-70 as the control head/altitude source, and a MX-20 as the primary display.

I did not look to see if the GNS 430W display showed the two targets - I'll try to remember that next time.

Anyone else seen this? My thinking is that in some cases, the ADS-B transmitter sends out two targets as it may receive two inputs (ADS-B out and radar?), the MX-20 traffic application is not filtering duplicate data, or the ADS600B is not filtering...
 
Yep, on my Dynon SV w/ their dual-frequency ADS-B in box. Two targets, one on top of the other, velocity vectors *almost* but not quite identical in direction.

Must be data coming from two different sources.
 
Thanks - glad to know I'm not the only one!
Hopefully, this is an issue that the FAA will address - if they're transmitting both - or make the ADS-B in Vendors fix it - in that case the NavWorx holders are screwed!
 
This will happen occasionally. Spelled out in the GDL90 specs:

MFD Recommendation: The uniqueness of the Target Identity depends primarily on the
equipment installer configuring the ADS-B equipment with the correct ICAO address. For TISB
targets, uniqueness also depends on the ability of the ground-based TIS-B processor to fuse
radar and ADS-B reports into track file IDs accurately. Neither of these processes can be
expected to always generate a unique identification. Therefore, Display vendors are advised to
take appropriate measures to cope with the possibility that the Target Identity alone may not
always be sufficient to uniquely identify duplicate targets. This caution includes the possibility
of reception of an ownship ?shadow? TIS-B target.
 
As Bob says, above.
But, double check that your ADSB-out is correctly configured to show your ADSB-in capability - one frequency or two frequencies.
 
With the 600B, there is no choice to set what frequencies your IN is listening to. It is hardwired to UAT only, as that is what the internal 600B IN receiver listens to.

So the ground stations think you are NOT listening on 1090 with your IN. The ground then rebroadcasts those 1090 targets on the UAT frequencies.

You get a double reply, one from the 1090 direct in your receiver and one rebroadcast on 978. Interesting that they show as quite close.

Since you can't change the 600B setting, your only choice is to put up with the double targets or to disable the 1090 IN on your IN contraption, probably a bad idea as if you are too low to get towers you will miss 1090 targets that you could see directly.

As your 430 is hardwired to the 600B, it will not have this problem, but it will only show 1090 targets if the UAT re-broadcast is being received.

BH

ADS-B Some of the traffic some of the time!
 
I dont know about the 600B but most systems prioritize the signal received directly from an aircraft over one received via a ground station. The problem arises when the ground station reported position is "different" from the one directly received. Most often if maneuvering while in Center Radar coverage only, which takes 12 seconds between update. The good thing is that is the equipment normally figures it out after a few seconds, but not always.

:cool:
 
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I dont know about the 600B but most systems prioritize the signal received directly from an aircraft over one received via a ground station. The problem arises when the ground station reported position is "different" from the one directly received. Most often if maneuvering while in Center Radar coverage only, which takes 12 seconds between update. The good thing is that is the equipment normally figures it out after a few seconds, but not always.

:cool:

Galin del 140ACW radar de Punta Salinas ?
 
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