Ghosting

[malcolmR]

I installed external aerials on my champ over the winter and have adsp out on my transponder using the paw gps. Since then  I have been plagued with what I assume is ghosting. I did not have this with internal aerials.   I get multiple danger warnings/red circles  giving heights above and below in rapid succession.  Warning frequency seems to drop/disappear when am remote from airfields/strips  and I am wondering whether it is assocaited with proximity to atom stations.  I am as sure as can be my device is configured correctly and have only one a/c on my skydemon.  Any advice or suggested investigations welcome.

Malcolm Rogan
G-DHAH

[PaulSS]

HEX codes have been known to change themselves, especially with an update etc. I would double-check your HEX code is correct in the configuration page.

What transponder are you feeding for ADSB Out?

[malcolmR]

trig transponder.  vector output shows paw has correct hex code

[PaulSS]

I would still check the config page to make sure it is right.....it only takes 5 seconds.

You haven't got SafeSky running in the background on a phone or similar have you? I've seen that spew up contacts and it took ages to track down the problem. It wasn't until the owner said he'd just check something on SafeSky and took his phone from his rucksack that the penny dropped 

[steveu]

I would still check the config page to make sure it is right.....it only takes 5 seconds.

You haven't got SafeSky running in the background on a phone or similar have you? I've seen that spew up contacts and it took ages to track down the problem. It wasn't until the owner said he'd just check something on SafeSky and took his phone from his rucksack that the penny dropped 

These are the top two reasons for me so I would endorse this solution.

[Admin]

If you have adsb out, you should see two emitters on vector, is this the Case ?

[malcolmR]

Yes - looks good coverage from both.

Haven't had chance to check hex code on device but I assume coverage from vector shows this correct.  Will do so this week.

Beginning to think I really had multiple a/c above and below within 500 ft and seeing none which is rather alarming!

[exfirepro]

Hi Malcolm,

You certainly should check that you have the same (correct) ICAO Hex for your aircraft in each device you are using. Although rare, it isn't unknown  for the HexID in PAW to revert to the default 'MAC-based' HexID. I have however also found the wrong code in transponders on several occasions.

That said, multiple Red Circle 'Danger' warnings can only be generated from Mode-C or Mode-S equipped aircraft - which can include high power responses from CAT aircraft on the ground at major airports to ground radar interrogations. This would be consistent with your report. These can be picked up and reported at a fair distance from the airfield (they usually appear suddenly as a 'Red' 'Danger' warning without going through the preliminary 'Green' and 'Amber' stages. If this is what you are seeing, try reducing the Bearingless Traffic reporting range in your PAW Configure Screen, and also consider restricting your selected relative altitude reporting level as well. (Don't forget to 'Save' the changes before exiting the Configure Screen).

The other issue that can cause 'rogue alerts' is close proximity between your transponder and PAW 1090 Receive antennas, which has been known to overload the front end of the 1090 SDR, though I know Lee did a lot of work in previous software versions to try to eliminate this issue. How far apart are these two antennas on your aircraft?

Let us know what you find and whether these suggested changes resolve the issue for you.

Regards

Peter

[malcolmR]

Peter

sorry so slow in responding

Altitude setting for bearingless targets was already at minm 500'.  I have reset range from short to ultra short and the problem appears to have gone on my trip henstridge to lundy and return today although I supposethat I need to fly in a more traffic intense region to be sure.

Aerials are side by side across the boot cowl with separation of 19inches

I will give a confirmatory [ I hope] update  after a few more flights

BW

Malcolm

[exfirepro]

Hi Malcolm,

Thanks for the feedback.

Ultra-short range was designed specifically for operation in (very) close proximity to major airports because of the high-power ‘Ground Mode-S’ issue. I fly from a small airfield about 25 miles from Edinburgh and if my Rosetta is on Long Range it can pick up CAT Mode-S on the ground at Edinburgh pretty much as soon as I’m in the air.

Ultra-short range isn’t recommended for normal use as you risk ‘normal GA power’ transponders getting very close before their Mode-S will trigger a warning (assuming they aren’t already reporting as Mode-S 3D moving aircraft via ATOM or iGRID of course). I normally fly with Bearingless on Medium Range, but you should be able to use Medium or Short Range without ghosting issues. If you can’t, I’d try experimenting with the position of your PAW 1090 antenna (for example with a PAW end-fed dipole (the standard Rosetta 1090 antenna) or PAW ‘internal’ dipole) and see if that resolves the issue. I have mine about a metre apart (about the max I can achieve on a flexwing) and have no ghosting issues.

If you are still having problems get back in touch.


Best Regards

Peter

[ILIMB]

Did you fix the issue? I occasionally have the same problem, with a portable setup, and if I check the aircraft callsign is always an aircraft that is plausible. The Hex value corresponds to the transponder's. It's kind of scary.
Multiple times I tried to carefully "separate" from the "ghost" but did not get a distinct trace.
What's very strange is that on the radar I don't see them, only on Skydemon. Could it be a FLARM protocol issue?

[steveu]

Did you fix the issue? I occasionally have the same problem, with a portable setup, and if I check the aircraft callsign is always an aircraft that is plausible. The Hex value corresponds to the transponder's. It's kind of scary.
Multiple times I tried to carefully "separate" from the "ghost" but did not get a distinct trace.
What's very strange is that on the radar I don't see them, only on Skydemon. Could it be a FLARM protocol issue?

As I understand it, it's not the aircraft call sign that prevents ghosting but the ICAO code. This for mode S, not sure about mode C...

[ILIMB]

I don't understand the comment, sorry. I wrote that the HEX code matches the transponder's, didn't mention the callsign. For every aircraft I fly I set up profiles with hex codes matching the transponder's. As recommended, the hex values are also checked with FlighRadar's and I only fly with S transponders.

I only mentioned "callsign" with regards to what appears on the screen, meaning that the conflict is always another aircraft's. But in reality there is none, and also the "ghost" is only on Skydemon, not on Rosetta's RADAR.

[Admin]

can I ask a few questions

Did you fix the issue? I occasionally have the same problem, with a portable setup, and if I check the aircraft callsign is always an aircraft that is plausible. The Hex value corresponds to the transponder's. It's kind of scary.
Multiple times I tried to carefully "separate" from the "ghost" but did not get a distinct trace.
What's very strange is that on the radar I don't see them, only on Skydemon. Could it be a FLARM protocol issue?

What you are describing is a Mode-S return which contains no position report, but does report an altitude
With no position, it cannot be plotted on a moving map

This is not ghosting, this is a correct detection.

you say you do not see these on the radar, only on skydemon
Can you provide your settings. and also describe exactly what you see in skydemon

Thx
Lee

[ILIMB]

Thanks for your reply, next time it occurs I'll take screenshots/record a video of the screen.

Essentially, without no prior warning, I instantly see an amber or red circle around my airplane on Skydemon, and an aural warning about the colliding traffic, often same altitude or slightly above/below.

Due to airspace limitations, were always flying at 1500aal (2000amls), and I often wonder if I'm picking up signals from aircraft on the ground.

But nevertheless, once the waning is out, I cannot see any trace of the other aircraft. Anyway, I'll try and provide more details, also about the configuration once I'm flying.