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Messages - a.alexeev.p

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1
General Discussion / PAW Classic For Sale
« on: July 15, 2023, 01:27:50 pm »
Saying goodbye to my classic unit as got Rosetta now as a gift.

I have done my best to upgrade the device for a more user friendly installation in the cockpit with antennas and GPS on extension cables with suction cups. NooElec SDR and 1090 antenna replaced the original ones. iGrid enabled and dongle included. Licence till feb 2024.

Will post on ebay shortly with lots of pictures and further details. Meanwhile feel free to ask any questions.

£145

UPD
https://www.ebay.co.uk/itm/256142467008?mkcid=16&mkevt=1&mkrid=711-127632-2357-0&ssspo=WxJr5MEdTlS&sssrc=2051273&ssuid=WxJr5MEdTlS&var=&widget_ver=artemis&media=COPY

2
Ok, so…. This time I spent a good amount of time trying different settings of a SE2.

I tried:

1) transmit setting at 0 kts and at 10 kts
2) position SE2 within 2-3 meters of paw and within 10-15 meters of paw
3) Ensured that the actual aircraft was parked and OFF

This time I did not manage to replicate the bearingless target issue in any configuration…in fact, initially SE2 signal did not show at all. After a couple of reboots it did show on SD via PAW with either transmit setting and distance from PAW.

Very inconclusive tests to be honest… the only thing that remained consistent was that SE2 was always visible on a flight tracking app (even when not visible on PAW). I know for sure that in principle (and probably in most cases) I do see SE2 from flying aircraft. But what happened here will still remain a mystery.

3
I must admit I was in a rush and didn’t look at that to be absolutely sure, so will make sure to confirm. However, don’t see how it would show on a plane tracker if it wasn’t transmitting… hence I am quite sure setting is set to transmit always, but will check

4
Hi Lee,

I just borrowed the SE2 from the aircraft owners for 5 minutes for my testing, so I suppose what the actual aircraft has is less relevant? But normally the aircraft is flown with a Mode S transponder + SE2.

The SE2 was visible on a flight tracking app - same as before with exact position and ADSB source confirmed. I placed it a few meters away i.e. my PAW was inside an aircraft and the SE2 on tip of the wing.

It was purely stationary ground test with no engines running or anything.

Regards,
Alex

5
So I attempted to replicate the issue… didn’t have much time, so I admit I did not see bearingless ring in SD, but I didn’t see the SE2 position either. On traffic page the aircraft of interest (GDBOD hex 40632C) was showing as CS only.

In the log found the following line:
$PALOG,20230516,162817,PAWRT,40632C,1,A,1,C,1,S,0,ES

Any more thoughts or suggestions of what I should try?

6
Exactly right! So what I think the issue is that when aircraft is shut down - a SE2 likely to be left on. An easy thing to miss as I sometimes have forgotten to unplug power from my paw in the past

7
Thank you so much for being so detailed an helpful once again :-) and hope the event went well!

So, the software version was 20230316

1) Apologies I probably sounded a bit confusing here. So it was nothing about transmission really... In the screenshot attached (hopefully readable) is playback of me flying GLOOC that only had Mode S transponder and sub sequentially MLATed by PAW atom network on the morning of 19th of April. The playback contains a big "jump" to the south, which did not occur in reality. So, if my friend was in another aircraft nearby with PAW and 3D Mode S enabled, then it sounds like s/he would see GLOOC quite far away from the actual position?

2) Thanks a lot! All makes sense. I was able to figure out from your playback system that that aircraft likely had Mode S + PAW, so what you explained totally makes sense and no questions on it.

3) GDBOD is another aircraft that was just next to GNXOE. It is a club aircraft that also normally has a CAP1391 onboard, also was parked and completely shut down, so I am very reluctant to agree that something was not right with the transponder as both aircraft were definitely off completely. I need to see if I can reproduce the issue myself, but I don't have a 1391 device available, so need to ask someone.

8
Also found the following log line:

$PALOG,20230417,152910,PAWRT,40632D,1,A,1,C,1,S,0,ES,0,P,0,F,0,U,0,M,00,valid,00,vers,00,nacp,00,nica,00,sil,00,sils,*07

which sounds like a signal was decoded as Mode AC only? As it was on the ground with engine off for a long time – there is no doubt on my side that that all standard electrics including normal onboard transponder were completely off at the time...

9
Edited

Alex,

That aircraft reports as a Cessna 172 out of Goodwood.

I don't of course have the full picture, but looking at PilotAware Replay and the PilotAware Database for the date in question, the aircraft was reporting what appears to be a very weak Mode S signal (via MLAT) around the south coast in the Goodwood / Selsey area from about 9:15am - initially operating what appear to be circuits out of Goodwood until about 09:30, but with pretty erratic position reporting. The weak MLAT reports on our network were to be fair probably partly attributable to the aircraft operating at very low level (less than 1000ft). It then appears again from about 10:30 to 11:30 - again as an extremely poor Mode-S (MLAT) signal, but with very occasional bursts of ADSB 18 - probably from a poorly sited CAP1391 device. It next appears from about 12:15 to 12:30 - again as a very irregular CAP1391 ADSB 18 Only signal between Goodwood, Selsey and Hayling Island, before suddenly switching from CAP1391 ADSB Only back to Mode-S again (as if the transponder was suddenly switched on) and thereafter showing a poor mix of ADSB / Mode-S MLAT back to Goodwood - again with extremely erratic position reporting (at low level) and lots of gaps. There is then a single 'ping' at 14:06 at 375ft (at Goodwood - presumably in the circuit or on the ground), followed by a re-appearance as a mixture of CAP1391 ADSB and MLAT in the Goodwood /Selsey/Bognor Regis area from 15:40 to 16:15, after which it seems to be operating as purely Mode-S at a fairly consistent altitude of between 750 and 950ft until it returns to Goodwood at around 16:50.

The erratic nature of the Mode-S reports would mean that PilotAware would keep changing between known-position (when the MLAT is reliable) and Bearingless (when it is not) and the aircraft would be reported as such on SkyDemon (provided you had 'Show Bearingless Targets' enabled). This would certainly explain (at least as far as I can tell from what you have sent us) what you were experiencing - i.e. intermittent known position reports from the poor MLAT/CAP1391 interspersed with random intermittent Bearingless target reports from the Mode-S - NOT the CAP1391.

It's certainly one of the most erratic reports I have ever looked at. If it was my aircraft I would be extremely concerned about the poor quality signals which appear to be being transmitted from it - with ADSB CAP1391 (perhaps understandably) only reporting out to less than 10Km, but my greater worry is the extremely poor quality of the MLAT reports which may well indicate a problem with the aircraft's Mode-S transponder.

Best Regards

Peter
p.s. you can check this for yourself at https://playback.pilotaware.com/playback/groundstations/ by selecting the Transmission Type, putting in the ICAO code and Start Time (3 hour segments max, though shorter periods give a more detailed expanded report) and clicking on 'Search'.

Thank you so so much! All super interesting and very details and triggered lots of thoughts, so might not be a short answer from myself either as some points are carry over from the original post idea and some completely new :)

1) The erratic behaviour you shared – does that mean that if I have mode-s 3D enabled – I am fairly likely to be displayed with similar output in my PAW? If so – I must admit I would probably go for disabling the 3D MLAT as got me thinking that I might be wrongly looking for a plane in a certain direction, so rather look all around due to a bearing less notification.

2) I in fact flew today and experienced a situation when an aircraft was first showing as bearlingless target and then next minute as a specific position. My Mode S 3D was disabled then, so in such circumstances it would totally make sense that possibly that other aircraft had some portable device that was visible sometimes to my PAW but not always. See first screenshot attached.

3) I have to point out that original question is unfortunately still remains a bit of a mystery because it was not really about MLAT or anything. I know for sure that they left a CAP1391 on by mistake in a parked and completely shut down aircraft and I was only 50m away from it, but still saw it as bearing less through PAW (second screenshot).


10
Thanks Lee! Yes sure:)

40632D around 14:30-15:00 UTC on 17th April 2023

11
I can definitely try and ask, however, as a flight tracking app was definitely showing it’s position on the ground (definitely not MLAT) and clearly marking it as ADSB - then it is fair to assume it was transmitting?

12
Thank you:) I think I’ll stick to Rosetta for now. The classic also started to have issues of seeing a lot less targets even after changing SDRs it shows a lot at first and then starts to die after a few months again. But that was still very insightful and helpful thread:)

13
Just to reconfirm:

Aircraft does have a mode s transponder only (not ADSB), but it is not very relevant because it was parked and completely off, just the pilot left their 1391 device on. I am sure of that also because on a flight tracking app I could see the exact position and clear marking that the signal was ADSB.

Two different PAW devices were nevertheless showing it as bearingless. When the the aircraft took off later - it started to show normally (although I can’t be 100% sure if when showing normally it was direct from the 1391 device or Mode S MLAT function of PAW). It was still showing as ADSB on the flight tracking app.

14
That’s a very useful, detailed and complicated story:) I did upgrade to Rosetta indeed in the end, but classic is still working I guess. How come you say though there aren’t any suitable chips anymore? I was pretty sure I saw on amazon wifi dongles that look exactly like the old ones for classics? Or they aren’t same on the inside?

15
I don’t recall the exact version, but it was the latest one that was released in the past 1-2 months. Same behaviour on my old classic paw and my friend’s brand new rosetta. It is just the classic picked up one aircraft and rosetta another (both with SE2 left on).

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