Author Topic: Ghosting  (Read 6791 times)

jbone

Ghosting
« on: January 02, 2021, 08:12:42 pm »
Hi,  Can someone tell me please how to fix this ghosting of my own aircraft that appeared on a flight in November (I hadn't changed anything from before).   It followed me right across the country and pretty much prevented me from noticing any other aircraft.    I attach a couple of screenshots from Skydemon.    The aircraft transponder is a non-ADSB Garmin GTX328 (mode S) and I have checked the HEX code on both that the PAW unit are correct.   I can only presume the PAW is somehow receiving MLAT information with the aircraft ID missing?

I didn't think at the time to try turning off the transponder and a soggy runway has stopped me flying again since.   I turned it all on again today in the hangar (as it happens with a PAW ground station just 50 meters away) and the ghost wasn't there, which is what makes think its MLAT.    My PAW is a classic unit set up as a perminant installation with external antennae.

I want to sort it before I spend some serious dosh on an ADSB out solution,

Thanks, John

jbone

Re: Ghosting
« Reply #1 on: January 02, 2021, 08:14:07 pm »
Screenshot of the ghost...

exfirepro

Re: Ghosting
« Reply #2 on: January 02, 2021, 11:25:58 pm »
Hi John,

Your SkyDemon screenshot clearly shows a ‘known-position’ aircraft, though obviously not present in the location shown. Was it displayed in the same position throughout your flight, or did it’s position vary? Do you have any other screenshots?

From your Configure Screen you have both Mode-C/S (which would show Bearingless ‘Rings’) and Mode-S/3D (which would show uplinked Positional targets for ‘in range’ Mode-S equipped aircraft) disabled - so it can’t be a ‘Bearingless’ Mode C/S signal or anything to do with MLAT (that’s what uplinked Mode-S/3D is)!

The only things you can therefore receive (all of which would display as known position targets) are a directly received PilotAware or ADSB signal, or an uplinked FLARM signal from a Ground Station. I take it you didn’t have any other position transmitters deliberately or accidentally running in the aircraft (a SkyEcho for example)?

Looking at G-INFO, your Hex ID in your PAW certainly matches your Aircraft Reg, and you say you have checked your transponder settings (always worth rechecking though, just in case). If that’s definitely OK, and you definitely didn’t have another device running in the same aircraft, the issue has to be something to do with proximity between the PAW and Transponder 1090 MHz antennas or the PAW and transponder itself.

I see from G-INFO that it is an RV9 - Where in the aircraft are the PAW and transponder units mounted? How close together?

What type of antennas are you using for PilotAware (i.e. Standard Rosetta / Remote Internal or Remote External) and for the Transponder and where are they fitted? and...

How far apart are the PAW 1090 Rx and Transponder Antennas?

I would BTW also advise doing a software update as you are still running version 20190621 and we are now on version 20201101 - running old software certainly won’t improve the situation.

Regards

Peter

jbone

Re: Ghosting
« Reply #3 on: January 03, 2021, 11:45:30 am »
Hi Peter,  Thanks for your response.  I'm afraid I didn't notice if the relative position of the ghost changed slightly during the flight, but it was "on top of me" the whole time.  I probably should have fiddled with it some more at the time, but in an unplanned situation I tried to force myself not to get distracted by it too much.       

I always get the 3Pi and ADBS-in antennae confused in my head, but if I've got it right, the 3Pi antenna is on the right underside of the fuselage, just aft of the main spar, and the transponder antenna is on the left underside, aft of the back wall of the baggage compartment (and they are 1.3 meters apart).  The ADBS-in antenna is in the cockpit, on top of the turtle deck facing the sky and there is a flarm mouse right next to it.   The setup has been like this for over two years with no problems.  It's a classic PAW and it's mounted by my left knee, so next time I fly I should be able to pull out each USB in turn to see if that makes a difference. 

Given your response that it's not MLAT, what is really confusing me is that I'm not getting the problem on the ground.  I attach a screenshot taken this morning (the contact is my ground station).   The HEX code in the transponder is definitely correct, I even took a photo so I could convince myself afterwards I wasn't going mad! 

There were no other EC devices on board.   I've been trying to decide between upgrading to a Garmin GTX 355 or just get a Skyecho, but I'm a bit nervous of compounding these sorts of problems if I go for the Skyecho. 

Thanks again, John

Ian Melville

Re: Ghosting
« Reply #4 on: January 03, 2021, 02:42:02 pm »
Ah,
Flarm mouse. That may be seen by the ATOM stations as a separate entity and transmitted back to your PilotAware? What ID do you have programmed into the mouse? IIRC it will need the same ICAO hex code at least.

Cheers
Ian

Admin

Re: Ghosting
« Reply #5 on: January 03, 2021, 02:51:42 pm »
Hi John,

I think Ian has spotted the issue, you must have a different ICAO code programmed to your flarm mouse.

thx
Lee

exfirepro

Re: Ghosting
« Reply #6 on: January 03, 2021, 03:45:12 pm »
I always get the 3Pi and ADBS-in antennae confused in my head, but if I've got it right, the 3Pi antenna is on the right underside of the fuselage, just aft of the main spar, and the transponder antenna is on the left underside, aft of the back wall of the baggage compartment (and they are 1.3 meters apart).  The ADBS-in antenna is in the cockpit, on top of the turtle deck facing the sky and there is a flarm mouse right next to it.   The setup has been like this for over two years with no problems.  It's a classic PAW and it's mounted by my left knee, so next time I fly I should be able to pull out each USB in turn to see if that makes a difference.

I would agree, if it is a FlarmMouse running it’s default Flarm ID, that would certainly cause the problem - but (unless I am very much mistaken), the thing I am seeing in the second photo immediately to the right of the 1090 antenna on the turtle deck is a PAW Mouse GPS - NOT a FlarmMouse!

@John, can you please confirm whether you definitely have a FlarmMouse (but not showing in the photos).

Edit: Also, just to clarify - your ground station in your 3rd screenshot is still showing as an aircraft. If you update your PAW software to the latest version as I suggested earlier and also check that you have the latest version of SkyDemon, it will then show Ground Stations as Masts, which is much less confusing.

Best Regards

Peter
« Last Edit: January 03, 2021, 04:35:40 pm by exfirepro »

jbone

Re: Ghosting
« Reply #7 on: January 03, 2021, 05:24:01 pm »
Peter, Ian, Lee,

My understanding has always been that's the Flarm mouse in the photo.  I certainly ordered one (in December 2017, Order number 1819)!   The GPS receiver looks more like a USB stick.   You can seem them both in this other photo, with the mouse on the left and the GSP receiver (which is painted black to stop it reflecting in the windscreen) on the right.   I could have completely misunderstood however. 

I just checked the instructions I used to set it up (20170721) and I don't see anything in there about programming the Flarm mouse with a Hex code.  I've never been very clear on whether it was a Tx/Rx or Rx only.   I certainly didn't set it up in any way, I just plugged it in.

If the consensus is its actually a GPS receiver, then I seem to have two.   Otherwise, if it's a Flarm Mouse, can you please point me to the instructions on how to enter the HEX code?   

If there is still uncertainty, I can always unplug it and see if I lose the GPS signal?  The plane is hangared at home, so I can do that faily easily.

Thanks, John

James Rose

Re: Ghosting
« Reply #8 on: January 03, 2021, 05:31:37 pm »
Hi John,

Could you upload your PilotAware .trk file to http://aircrew.co.uk/playback/ from the 4th of November and send me the link once uploaded?

James

Ian Melville

Re: Ghosting
« Reply #9 on: January 03, 2021, 05:34:21 pm »
Not Like any FLARM Mouse I have seen before, and there is no FLARM antenna. It looks like the VK-162 G-Mouse USB GPS.

If that is the case then my theory gets thrown out of the window.

Quote
I certainly ordered one (in December 2017, Order number 1819)
from who? BTW is it connected to your PAW?
« Last Edit: January 03, 2021, 05:36:52 pm by Ian Melville »

jbone

Re: Ghosting
« Reply #10 on: January 03, 2021, 07:44:17 pm »
I've been to the plane and disconnecting the 'mystery' mouse does NOT cause loss of GPS signal.   It is stuck down and I'm reluctant to pull it off, so I cannot read what's on the underside.  Disconnecting the small dongle that looks like a datastick does cause loss of GPS signal (and before I sprayed it black, it had the words "GPS/GLONASS" written on it - I know because I've got a spare)!   However I also found a 2017 receipt from Pilotawarehardware for a "GPS Mouse on 195cm lead".   So I am thoroughly confused now.  Perhaps I got two GPS receivers, and when the kit arrived and I saw "GPS" written on the dongle and just assumed the other was the Flarm dongle I had wanted (and thought I had ordered).  I cannot find a receipt for a Flarm dongle however, so perhaps I don't have one and I just confused the debate by mentioning it. 

In which case we are back to the drawing board.  All offerings welcome please? 

Also (James), the track file for the problem flight (on the 4th November 2020) is missing from the list (on the screenshot).   Maybe PAW just failed that day for some reason.   (It does have a good Anker power supply, so that's not the reason.)  I've just done a software update today, so maybe that will help in future. 

Ian Melville

Re: Ghosting
« Reply #11 on: January 03, 2021, 08:02:21 pm »
Yes it looks like you have two GPS. The GPS Mouse is an optional extra. One GPS will come with the PAW unit.
I would leave the GPS mouse fitted and remove the other one. Then you have more options to place it for best reception.

PilotAware does not sell FLARM products. That would be a bit like a Ford dealer selling Toyotas :-)
« Last Edit: January 03, 2021, 08:05:44 pm by Ian Melville »

Ian Melville

Re: Ghosting
« Reply #12 on: January 03, 2021, 08:07:56 pm »
Just noticed that your 3rd Jan Ghosting example is on the list available for download

exfirepro

Re: Ghosting
« Reply #13 on: January 03, 2021, 08:39:46 pm »
Hi John,

Thanks for the feedback.

The dongle you painted black is the standard GPS dongle which would have been supplied with your PilotAware Classic - fitted on a USB cable to extend it up onto the turtle deck so it has a good view of the sky.

The other one certainly isn’t a FlarmMouse (I have two of them). As Ian has said, it looks very like a VK-162 remote GPS Mouse as sold as an option by PilotAware Hardware.

When you say...  ‘disconnecting the ‘mystery’ mouse does NOT cause loss of GPS signal’ - I am intrigued. I presume you mean you unplugged the other end of the cable that disappears into/behind the dash...  but can you explain or describe what exactly you disconnected it from ?

Regards

Peter

p.s. Quick question for Lee - if both GPSs were plugged into the PAW at the same time, could that cause two slightly different positions to be fed to the Bridge?



James Rose

Re: Ghosting
« Reply #14 on: January 04, 2021, 10:36:27 am »
After looking at the track files from 3rd Jan, the other plane ground station. As you were running PilotAware version 20190621, SkyDemon displayed it as a plane. Latest versions of PilotAware and SkyDemon now show a ground station.

Why the plane was following you on the 4th Nov is a mystery. My guess would be it was also a ground station and some bug with using a 2019 PilotAware release with the latest SkyDemon was causing it to be displayed incorrectly. I believe after you update to the latest PilotAware you shouldn't have any issues.