Weak P3i transmission?

[grahambaker]

Hi,

I have PAW in the cockpit, and ADS-B out via certified Mode S-ES from a Trig Transponder, the source being a GNS430W.

Since the upgrade to the latest version (athough I can't put my hand on my heart and say it's definitely aligned with that) I've noticed that Vector is indicating that ground stations are barely picking up my P3i signals. I'm using PAW as a position/traffic source for two copies of SD and there has been no problem with track recording, nor is it failing to pick up and display traffic. This is definitely a new thing, and the location of the PAW has not changed. I would previously often get PAW detected at up to 60-80Km, with a good forward radial coverage.

Vector diagrams for the last 5 flights over two days as follows, PAW first and ADS-B out second.

Any ideas?

Graham

[exfirepro]

Hi Graham,

That Vector diagram certainly suggests that either your PAW has stopped transmitting, or you simply weren’t in range of enough Ground Stations (which I doubt).

Three possibilities.

1. Your licence has expired.

2. You didn’t have a full GPS fix (though I’d have thought you’d have noticed that one).

3. Although it shouldn’t happen, the unit might have reverted to its default Hex ID. If so, it won’t report transmissions under your ‘real’ Hex ID, but under the default one instead.

If you aren’t near the plane give me the last 5 digits of the unit’s 12 digit MAC code (the one that starts B827EB.... which you can get from the unit or from your last licensing email) and I can check the database for you (or you can check yourself on Vector - the default Hex iwill be the last 5 digits of the MAC code preceded by the letter ‘F’ so for example F12A3B or whatever.

Please let us know how you get on.

Best Regards
Peter

[grahambaker]

Hi Peter,

Thanks for the reply.

1. Licence has definitely not expired!
2. I happened to snap the config page during one of the flights - 3D fix with 11 of the 12 in view satellites in use. The SkyDemon tracks were unbroken for the flights.
3. I’ve checked Vector for the default hex as you suggest, and no hits were reported.

I’ve attached the config page if it helps with any further ideas.

[steveu]

I think we need to check that all cable joints are done up properly and that the aerial is not knackered.

Be worth, with the PAW tuned off, unscrewing both ends of the P3i aerial cable and checking that the centre pin has not dropped off or got bent at either end, then buzzing both the inner and outer for continuity between ends.

[exfirepro]

Hi again Graham and thanks for the additional information.

That screenshot is of course your Home Screen, not the Config Screen, but I can see nothing obviously amiss there, though the P3i figures look suspiciously low. It would also be useful to see a shot of your Config Screen since your last update, though the only things I can think of is the aircraft type setting (Base Stations) and the new VSO setting, which is specifically designed to stop PAW transmitting when stationary or at low speed (and will of course also stop transmission at high speed if the threshold has been set too high).

Remind me - is the P3i antenna fixed direct to your Rosetta or are you using remote antennas? If remote are they internal or external? Have you had a chance to check the continuity yet as suggested by Steve?

If all that is OK, the next thing I would check that the Bridge board is still properly seated onto the GPIO Pins on the Raspberry Pi, but that of course requires opening the case. If you haven’t done this before, it involves first removing the power cable, the removable case end cap, the P3i antenna or cable and the nut/washer on the P3i SMA connector. Also remove the microSD card as it is easy to snap it when the case comes apart. You then need to locate the hidden clips which hold the upper and lower case halves together. There are two each side, one between the microUSB and HDMI port and the other between the audio port and the case end. They can be popped by gently inserting a thin blade between the two halves of the case at the clip locations and then firmly but carefully pressing the blade in to pop the clip. I find it easiest to do this side first, one at a time, then release the clips in the equivalent positions on the other side.

Once open, check that the Bridge is correctly seated, and that the SMA connector is still properly attached to the board. If that is OK, you can reassemble the unit, taking care not to catch the pigtail cable for the 1090 SDR where it passes the USB ports and reinsert the microSD card. The only other thing I can think of at this stage which would be likely to cause the unit to stop transmitting is some sort of software corruption during the upgrade. This would require reformatting and reloading the software or loading a fresh copy from the http://pilotaware.lode.co.uk site onto a new card.

Please keep us posted as to what you find.

Best Regards
Peter

[grahambaker]

Peter,

Thanks again for the comprehensive reply. Of course, it was the Status page and not the Config page I'd sent! Unfortunately I didn't have that saved at the same time. The antennae are standard Rosetta attached to the casing.

I'm going to fish the box back from the aircraft today and try some bench checks as suggested. Once iI've found the time to do that I'll let you know how I get on.

Regards

Graham

[JCurtis]

As I've posted elsewhere before...

If the SMA connector is damaged on the Bridge, I generally can repair them for the cost of the connector and return shipping.  I ask you make a donation to your local air ambulance as payment for the repair.
With the whole PilotAware unit I can also check the RF output power of the Bridge board is OK too, if there isn't anything obviously wrong elsewhere.

[grahambaker]

Thankyou for the offer Jonathan.

I've opened up the box and to my untrained eye all looks in order. The Bridge was seated properly and the SMA connector seems to be robustly fastened.

Looking at the antenna itself, I slid the plastic body off the stub to reveal the inner cable. I assume that a length of shielding is left exposed, twisted and folded back to make contact with the metal inner of the antenna. If that is the case I was surprised that only four strands were of a length to acheive this. Image below.

Have I wrecked the antenna by opening it in this way? If not, should there be more of the shielding exposed to form a better contact with the inner sleeve of the antenna?

Once again, thanks to all for their suggestions.

[exfirepro]

Hi Graham,

I take it we are talking about the longer (P3I) antenna? Not sure I’d recommend taking one apart unless purely for interest after determining that it was definitely ‘dead’.

It’s what is technically known as a ‘sleeve dipole’ - in this case made by stripping the outer covering and braided shield off a specific length of coaxial cable, the upper (exposed) length then becoming the radiating element, with the section of the outer braid still inside the black coating of the lower section acting as the matching ‘ground’ leg of the dipole. That being the case, there should strictly be no long braid wires exposed as that could affect the efficiency of the radiating element (though probably not to any great degree). The stray wires may of course have originally been twisted around the base of the radiating element at the ‘feed point’ and simply become dislodged as you pulled the cable out of its casing.

I guess a replacement will be required. If so, they are available on the PilotAware website - or now might be the time to consider upgrading to remote internal or preferably external antennas (after establishing that your unit is transmitting of course).

Best Regards
Peter

[grahambaker]

Latest update:

I’ve bought a remote internal antenna and tested the unit with it, with not much change in performance as far as ground stations are concerned. I’ve only seen one PAW equipped aircraft during this test and that was quite local, so not particularly conclusive.

All this lines up with updating to the latest version using the iOS app, so I thought I’d try a fresh install on a new SD card.

Having gone through that, now the bloody thing now won’t recognise my licence key, and is constantly telling me it’s expired. If I drop the old card back in, everything works (notwithstanding the range issue), so I need help please in sorting out why ia fresh install is not recognising a perfectly good licence key, even after multiple reboots.

Further update:

I noticed that SD card I’d used was only 4GB, so I tried again with a 64GB one, with the same result. I’ve also noticed that the Config page doesn’t show the three ‘positional contacts’ settings, nor the volume settings. Is that just because it thinks a valid licence key hasn’t been entered, or a sign of something else?

As a footnote I’d dropped my original ‘updated to 20220101 via the iOS app’ card back in, just to see if there was something wrong with the box itself, and it picked up a PAW (only) equipped aircraft over 30km away from inside my conservatory, so P3i receive works fine. It’s just I haven’t really been able to establish whether the transmit side is flakey.

Further further update:

I generated a new licence key from the pilotlode website and the fresh install now works! I'll try the box tomorrow and see how it performs on the P3i transmit side with a fresh install when airborne.

[exfirepro]

Hi again Graham,

Latest update:

I’ve bought a remote internal antenna and tested the unit with it, with not much change in performance as far as ground stations are concerned. I’ve only seen one PAW equipped aircraft during this test and that was quite local, so not particularly conclusive.

All this lines up with updating to the latest version using the iOS app, so I thought I’d try a fresh install on a new SD card.

Having gone through that, now the bloody thing now won’t recognise my licence key, and is constantly telling me it’s expired. If I drop the old card back in, everything works (notwithstanding the range issue), so I need help please in sorting out why ia fresh install is not recognising a perfectly good licence key, even after multiple reboots.

Further update:

I noticed that SD card I’d used was only 4GB, so I tried again with a 64GB one, with the same result. I’ve also noticed that the Config page doesn’t show the three ‘positional contacts’ settings, nor the volume settings. Is that just because it thinks a valid licence key hasn’t been entered, or a sign of something else?

As a footnote I’d dropped my original ‘updated to 20220101 via the iOS app’ card back in, just to see if there was something wrong with the box itself, and it picked up a PAW (only) equipped aircraft over 30km away from inside my conservatory, so P3i receive works fine. It’s just I haven’t really been able to establish whether the transmit side is flakey.

OK, after a bit of detective work, I've worked out that you have a PilotAware Rosetta - (or possibly an older Classic updated to a Pi3) - running in a metal bodied AA5, out of Welshpool ? (which has an active PilotAware ATOM Ground Station). Please confirm these details or advise otherwise.

You also have Mode-S/ES ADSB-Out from your Trig Transponder (fed GPS Data from your GNS430W) - which appears to be working as expected.

I've had a look at the PilotAware Database, which actually shows extremely variable P3i signal reports from your aircraft over a prolonged period from well before the recent software update, so I'd be pretty sure the software update wasn't the culprit.

The fact that you tried a new card with the latest software but it wouldn't accept your licence key, won't have helped of course. Without a valid licence key (and a solid GPS position fix) the software simply won't transmit, so if inserting a new card, you need to address these issues.

Looking at database reports from the latter part of last year, it is of significant note that while you have occasional (sometimes 'freak') reports from remote sites (presumably during flight) at ranges of up to 99Km, the reports from the Welshpool ATOM station itself are consistently from around 0Km maximum range. This would suggest that there is either a significant problem with Welshpool's P3i receiver (I will speak to Peter Greenrod about this), or more likely that the problem is due to either a faulty Bridge in your PAW, a defective antenna, or significant local obscuration of your p3i signals by the positioning of the unit / antennas inside the metal bodywork of your aircraft.

Looking at recent P3i reports on the database for example, I see two reports on...

8th March - Only 6 P3i data packets (about 12 seconds worth of transmission) received by PWecgw at a range of less than 10Km (maximum reported range was actually 0Km) - would indicate that the Bridge was 'trying' to transmit, but with no significant effect.

10th March - Only 2 P3i data packets received by PWegcw at a range of less than 10Km (with again a maximum reported range of 0Km) - again indicates no effective P3i transmission.

Reports from 15th March - presumably after you fitted the new PAW internal antenna - indicate a slight but minimal improvement with a total of 60 P3i data packets (about 2 minutes worth of transmissions) received by PWecgw (Welshpool) at less than 10Km (actual maximum reported range again 0Km), followed by 7 packets at up to 21Km as you approached (or left) PWcoedy, with a further 47 packets at less than 10Km range as you passed close by. A further 20 packets (40 seconds worth) were received at between 10 and 13Km as you approached (or departed from) PWDruids, with only 55 packets whilst you were within 10Km of Druids - all of which indicate extremely poor P3i transmission from your aircraft.

I did manage to find this flight on the Aircrew GroundStations Replay tool, which confirms that the Pilotaware signals from your aircraft throughout the flight were at best extremely weak and for most of the flight effectively non-existent.

You can see the flight for yourself by following this link...

https://aircrew.co.uk/playback/groundstations/?ICAO=4019F9&RxType=PAW&adbVariant=*&Station=*&start=1647345600&end=1647356400

...and setting the date/time to 15 March at 12:00 and a 3 hour reporting period, then clicking on the [Search] button. You can then follow the flight and see the Ground Station connections by dragging the marker along the lower part of the screen.

Unfortunately it is extremely difficult to determine the reason for the poor transmissions remotely, which in the extreme case could be due to signal obscuration related to the positions of the unit and antenna(s) within your aircraft (can you provide photos?), or of course a defect in the unit itself.

In view of the lack of definitive evidence to assist remote diagnosis, I am inclined to suggest a 'return to base' of your unit and ask Ash Vinning to run it on the test bench and see what is going on. If you want to go down this route please get in touch with Ash via support@pilotaware.com and let me know how you get on.
 
Sorry, I can't be of more help, but without direct access or considerably more information I'm banging my head off the desk and can't really see any other realistic way forward.

Best Regards

Peter

[grahambaker]

Peter,

Many thanks for the comprehensive investigative work, and it's interesting to note that you can confirm that the issues predate the software upgrade. The AA5 is not really an issue. I keep the Rosetta on the front of the coaming strapped to an Anker battery pack which gives good forward and side visibility - historically Vector show good range reception.

I tried the unit today (in a different aircraft, a C152, (hex code 401FFA) with the new remote antenna mounted vertically with the suckers in the front side of the windscreen) and a quick look at Vector shows that transmit performance remains less than par. This was with the fresh install correctly configured.

I'll contact Ash, but before I do, I'll see if I can borrow a spare bridge from Peter G here and give it a try.

Thanks

[exfirepro]

Hi again Graham,

401FFA has reported 199 packets from Welshpool with a maximum range of just 2Km, 61 from Coedy at less than 10Km and 21 at between 10 & 20Km - with a maximum of 17Km, and 7 from Druids at less than 10Km and 18 at between 10 & 20Km with a maximum of 12Km.

Those figures match what I am seeing from the unit when in your AA5, so reinforce the likelihood of a transmission issue from the PAW unit itself. The consistently low range reports from Welshpool, however also point to a potential issue with Welshpool's receiver. As I said previously, I will take this point up with Peter G and see if we can work out what the issue is there.

Best Regards
Peter R

[Ian Melville]

I'm wondering if the P3i connector has parted from the PCB? This is a weak area and prone to damage by a knock.

[grahambaker]

I'm wondering if the P3i connector has parted from the PCB? This is a weak area and prone to damage by a knock.

I’ve checked, and here is no obvious loosening or cracking. P3i reception seems fine, although I accept that the two are not the same.