Author Topic: Yet again - ghost target 100 feet above  (Read 16181 times)

rogerabc

Re: Yet again - ghost target 100 feet above
« Reply #15 on: August 03, 2018, 09:43:08 am »
Any eta for the software download please Lee?

Admin

Re: Yet again - ghost target 100 feet above
« Reply #16 on: August 06, 2018, 08:42:05 am »
Wilco.... hope to get them this evening and will send to you....

Hi Steve

had a brief look at your tracks, can you please confirm, are you selecting :-

Mode-CS, or
Mode-CS+Filter

Your tracks would indicate the Filter is not enabled.

Thx
Lee
« Last Edit: August 06, 2018, 08:43:42 am by Admin »

Steve6443

Re: Yet again - ghost target 100 feet above
« Reply #17 on: August 06, 2018, 10:20:30 am »
Wilco.... hope to get them this evening and will send to you....

Hi Steve

had a brief look at your tracks, can you please confirm, are you selecting :-

Mode-CS, or
Mode-CS+Filter

Your tracks would indicate the Filter is not enabled.

Thx
Lee

Hi Lee,

previously it was enabled, now it was just set on Mode-CS. Have set it to Mode-CS+Filter. Thanks.

Admin

Re: Yet again - ghost target 100 feet above
« Reply #18 on: August 06, 2018, 11:16:42 am »
Hi Lee,
previously it was enabled, now it was just set on Mode-CS. Have set it to Mode-CS+Filter. Thanks.

Well, you may not be pleased about that, but I am!
That makes me feel much better, looking at your track I was seeing a very powerful transponder (which is your own) which should have been filtered using the Machine Learning detector. The fact that I saw it repeating, indicated that the Machine Learning algorithm was either a bit ill-educated or not enabled !
Thanks for clarifying
Lee

PeterG

Re: Yet again - ghost target 100 feet above
« Reply #19 on: August 06, 2018, 02:27:28 pm »
I had a very similar issue when flying in a friends aircraft last week. I changed the hex code and stuff but throughout the flight I had the ghost image but with different C- codes.

I've checked as as far as I can see I was using the Mode CS + filter in the profile. Otherwise, the published HexCode on G-INFO was wrong.


Admin

Re: Yet again - ghost target 100 feet above
« Reply #20 on: August 06, 2018, 05:10:28 pm »
I had a very similar issue when flying in a friends aircraft last week. I changed the hex code and stuff but throughout the flight I had the ghost image but with different C- codes.

I've checked as as far as I can see I was using the Mode CS + filter in the profile. Otherwise, the published HexCode on G-INFO was wrong.

If you can provide the track files we can investigate what could be happening.
Hex Codes are irrelevant as far as Mode C is concerned I am afraid

thx
Lee

scsirob

Re: Yet again - ghost target 100 feet above
« Reply #21 on: August 06, 2018, 06:38:32 pm »
..Interesting the same encoder which has +/-125ft accuracy

 I recall that this is a left-over of parallel altitude encoders for early Mode-C transponders. They used octal encoding (just like the xprd codes themselves) and this allowed for a good trade-off between bits required and accuracy. A single octal digit (3 bits) is enough to encode 1000ft. Flight levels are divided up in 500ft increments (East/West, IFR/VFR), so having 125ft steps are plenty to have error margin and still keep things safe.

The fact that we now have cheap sensors that can do +/-10cm for penny's wasn't so obvious when the Mode-C standard was cooked up.

rogerabc

Re: Yet again - ghost target 100 feet above
« Reply #22 on: August 07, 2018, 06:05:46 pm »
Flew for 5 hours today with the engineering software release & have sent you the track files for analysis.

Best regards,

Roger

PeterG

Re: Yet again - ghost target 100 feet above
« Reply #23 on: August 09, 2018, 02:38:14 pm »
Can anyone please advise how to send a track file. When I tried it said there was a512kb limit.

Peter

Ian Melville

Re: Yet again - ghost target 100 feet above
« Reply #24 on: August 09, 2018, 05:05:07 pm »
There are two ways to do it.
Put in an online store like Dropbox, make it public and send the link to Lee.
Or
Email the file to Lee.

PeterG

Re: Yet again - ghost target 100 feet above
« Reply #25 on: August 09, 2018, 07:35:22 pm »
Cheers

davidbu99

Re: Yet again - ghost target 100 feet above
« Reply #26 on: August 18, 2018, 02:02:09 pm »
I've also suffered fairly frequent Mode C alerts although I've started to learn to ignore them due to the callsign format (e.g. C-0A60) and the fact they appear instantly as a red ring and fairly quickly disappear again. They are random in nature and I'm unsure what triggers them. On a trip to Newquay yesterday I had several. See a screen grab of SKD and the track file.

Example extracts from the Track file below. I'm assuming these are ghost targets. I've a GTX330 Mode S.

https://www.dropbox.com/s/pptipmxkgt7i4ii/2018-08-17_11-56.trk?dl=0

$PFLAA,3,1500,,-33,1,FF0A60!C-0A60,,,,0.0,8*04
AlarmLevel = 3
Rel North = 1500
Rel East =
Rel Vertical = -33
ID Type = 1
ID = FF0A60!C-0A60
Track =
Turn Rate =
GroundSpeed =
ClimbRate = 0.0
Aircraft Type = 8*04

$PFLAA,3,1500,,-37,1,FF0A60!C-0A60,,,,0.0,8*00
AlarmLevel = 3
Rel North = 1500
Rel East =
Rel Vertical = -37
ID Type = 1
ID = FF0A60!C-0A60
Track =
Turn Rate =
GroundSpeed =
ClimbRate = 0.0
Aircraft Type = 8*00

Admin

Re: Yet again - ghost target 100 feet above
« Reply #27 on: August 20, 2018, 12:51:08 pm »
Hi davidbu99

Can You please confirm your Mode C/S settings selections (or post your configure page)

thx
Lee

davidbu99

Re: Yet again - ghost target 100 feet above
« Reply #28 on: August 22, 2018, 09:39:20 pm »
Lee, sorry for the delay, attached.

Admin

Re: Yet again - ghost target 100 feet above
« Reply #29 on: September 04, 2018, 10:02:37 am »
Hi David

This is great data, I am sure this is you, and it has (just) bypassed the filter !
Basically your transponder encoder is disagreeing with the PilotAware alt encoder, here is the first message

$PFLAA,3,1500,,-31,1,FF0A60!C-0A60,,,,0.0,8*06

31 metres below, this equates to 101.7ft, the accuracy of a ModeC encoder is rounded to 100ft increments (PilotAware is 3ft increments) so this is just outside the scope of the filter - AARRGHGHH!

I have seen this a couple of times now, and I think we need to counter for the fact of this rounding issue in the ModeC Encoder. Interestingly, I can find nowhere where the Altitude encoder rounding mode is defined, it could be
- round up
- round down
- round to nearest
but not defined anywhere I have seen.

I think we can address this.
Other observation, previously I have seen this in ascent or descent, whereas in your case it looks like level flight. I wonder if there was suddenly a drop in external air pressure compared to internal air pressure perhaps ?

Thx
Lee