Author Topic: Vector shows PAW but not ADS-B signals  (Read 10096 times)

GeoffreyC

Vector shows PAW but not ADS-B signals
« on: December 28, 2020, 08:34:08 pm »
Firstly thanks to all at PilotAware for the new Vector facility (and I see there’s a useful new explanation video on YouTube today https://youtu.be/VOoZPhzFNDY

Owing to bending my Quik-R in July and a long repair process I have only recently been able to try it out and see what results I got, and this was from the single post-repair check flight so it’s interesting to see the results with limited data.

PAW mounted in the front pod (on top of the battery) with the PAW antenna extended and in the front windscreen (this is actually a photo of the plane post accident, note the retractable undercarriage mod, but the antenna is back in pretty much the same position, perhaps a little more vertical):

Trig TT21 transponder, antenna underneath at the bottom back of the pod, connected to PAW for ADS-B

The PilotAware diagrams show I’ve got good 10km visibility (I was flying round the Everton base station), and some signal received at 40km.  Strongest is front and left, right is good as well, a definite black-spot at about 30 degrees (which I’m guessing is the front strut attenuating the signal) and poorer behind where my body and the fuel tank are in the way.
Think I will try moving the antenna further forward to see if I can resolve the front strut issue, but I’m fairly happy with this
« Last Edit: December 28, 2020, 08:46:18 pm by GeoffreyC »

GeoffreyC

Re: Vector shows PAW but not ADS-B signals
« Reply #1 on: December 28, 2020, 08:51:57 pm »
(continued)

What was surprising was that Vector reports NO ADS-B traffic at all.

My transponder was on, it was connected to PAW and was receiving a GPS signal,  and flightradar 24 shows my flight pretty much from when I left the circuit to when I returned back.   FR24 is using ADS-B to trace my route so I am confused

Geoffrey

James Rose

Re: Vector shows PAW but not ADS-B signals
« Reply #2 on: December 28, 2020, 10:28:04 pm »
Hi Geoffrey

Your flight on the 22/12/2020 you flew within 2 ground stations that were less than 10km away which were:

 - PWUKBIG which doesn't have an ADS-B in
 - PWEverton which does have ADS-B in but its extremely limited (the PilotAware range is 10 times better)

The 360Radar network (which feeds into the ATOM network) saw 285 ADS-B pings, however 360Radar data is not currently used in the beam graphs.
Flightradar24 saw around 40 ADS-B pings.

I am surprised that none of the other PAW groundstations saw your ADS-B, especially when PWEGBT saw your PAW at 60km.

Here are the groundstations which saw your PAW transmissions and your average distance to them.

Code: [Select]
PWEverton    3.5km
PWUKBIG      5.7km
PWUKGRL      10.6km
PWOrwell     14.1km
PWBedford    16.3km
PWOlney      27.4km
PWCambrid    30.0km
PWEGBKE      36.6km
PWEGBT       59.3km

GeoffreyC

Re: Vector shows PAW but not ADS-B signals
« Reply #3 on: December 29, 2020, 11:30:33 am »
Hi Geoffrey

Your flight on the 22/12/2020 you flew within 2 ground stations that were less than 10km away which were:

 - PWUKBIG which doesn't have an ADS-B in
 - PWEverton which does have ADS-B in but its extremely limited (the PilotAware range is 10 times better)

...
Thanks James, so that explains the lack of ADSB from the two most nearest ground stations, but does surprise me that there's no ADSB traffic received from anywhere else.  I know I wasn't particularly high, but Gransden Lodge and Orwell should have seen me OK.

Geoffrey

Smaragd

Re: Vector shows PAW but not ADS-B signals
« Reply #4 on: December 29, 2020, 12:53:08 pm »
This answers a question I was about to ask, but to wander slightly off thread, how does VECTOR differentiate between ADS-B and CAP1391; aren't they both ADS-B outputs?

James Rose

Re: Vector shows PAW but not ADS-B signals
« Reply #5 on: December 29, 2020, 01:15:31 pm »
This answers a question I was about to ask, but to wander slightly off thread, how does VECTOR differentiate between ADS-B and CAP1391; aren't they both ADS-B outputs?

The ADS-B packet includes 5 bits for the downlink format (DF). ADS-B is 17 and CAP1391 is 18, the groundstations decode this and store it in the database for VECTOR to query.

Smaragd

Re: Vector shows PAW but not ADS-B signals
« Reply #6 on: December 29, 2020, 05:13:04 pm »
Simples! Thank you.

GeoffreyC

Re: Vector shows PAW but not ADS-B signals
« Reply #7 on: December 30, 2020, 07:20:22 pm »
(continued)

What was surprising was that Vector reports NO ADS-B traffic at all.

My transponder was on, it was connected to PAW and was receiving a GPS signal,  and flightradar 24 shows my flight pretty much from when I left the circuit to when I returned back.   FR24 is using ADS-B to trace my route so I am confused

Geoffrey

Update:  the runway had dried out enough today to get up in the air again,  this time a much longer 2 hour flight around Bedford, Peterborough and towards Ely.

Looking on Vector, same/similar results.

A good set of PilotAware traces, 5676 contacts today, up to 60km away, and definite issue on front/right, caused I think by the front strut.  I could move the antennae in front of the strut but then I fear I'd get no rearwards signal,  I could mount it under the pod further back, but then great for planes below me, but what about above?

ADS-B does show 35 contacts, all very close range,  and again FlightRadar tracks me fine, screenshot of the latter half of the flight below.

And, another strange thing, Vector is showing 869 pilotaware contacts from 9th August.  They weren't there last week, I didn't fly then and in fact the plane was dismantled and PAW stripped out of it then,  so unless someone else was inadvertently using my ICAO hex code, these don't make sense.
« Last Edit: December 30, 2020, 07:31:14 pm by GeoffreyC »

Ian Melville

Re: Vector shows PAW but not ADS-B signals
« Reply #8 on: December 30, 2020, 09:07:12 pm »
That front strut is too close to the PAW antenna. I suspect it may be acting as a reflector and improving the signal to the left at the expense of the right.

Many microloghts and Gyros have the coms antenna on the top of the nose, as far forward as possible. Is that an option?

Deker

Re: Vector shows PAW but not ADS-B signals
« Reply #9 on: December 30, 2020, 10:52:23 pm »
Hello GeoffreyC,

I'm not so sure Flight Radar is tracking you very well.
There is a big section between  Clapham and Sharnbrook where there were no tracking points.

Oundle to Peterborough looks good, but 'jumpy' between Whittlesey and Gold hill and also jumpy in the St Neots area.
Note: there are approximately 3,000 Flight radar ground stations compared to approx 200 ATOM stations so the chances that FR24 picks up your ADSB transmission is much higher because you are likely never to be far away from an FR24 station.
Flight on the 22nd shows similar big jumps.
However, flights in July show a good signal being picked up, so has a connector been disturbed or something else changed?

I'd be looking at the ADSB antenna / cabling installation, FR24 (and Vector) are indicating a possible range problem.

Deker.


GeoffreyC

Re: Vector shows PAW but not ADS-B signals
« Reply #10 on: December 31, 2020, 12:31:31 pm »
That front strut is too close to the PAW antenna. I suspect it may be acting as a reflector and improving the signal to the left at the expense of the right.

Many microlights and Gyros have the comms antenna on the top of the nose, as far forward as possible. Is that an option?
Thanks Ian, I suspected that the front strut was causing problems to the right and Vector certainly shows it up in a very visible way.  Hadn't thought that the strut might be improving the left side as well as impacting the right.

Putting the antenna on the front of the nosecone is an option,  my pod had its radio antenna originally there and I know that Brian Montilla has his PAW one mounted on the front in the hole.   Following my accident I had a new pod made by Albatross (and they've done a good job of the fabrication), so would have to be drilling a hole in the virgin fibreglass  :(

Its not a position I favour because we store our trikes with the wings de-rigged and so have to drop the base bar over the nose of the trike every time we put the plane away and vice-versa to re-rig it.  I've caught the antenna with the bar on a previous trike and ripped the fibreglass as a result, so would prefer not to introduce that risk.

Having said that, it does make logical sense that this would maximise my front visibility, doubtless at some impact to rearwards.

Will look at Brian's traces and see how his PAW visibility compares to mine.

GeoffreyC

Re: Vector shows PAW but not ADS-B signals
« Reply #11 on: December 31, 2020, 12:40:06 pm »
Hello GeoffreyC,

I'm not so sure Flight Radar is tracking you very well.
There is a big section between  Clapham and Sharnbrook where there were no tracking points.

Oundle to Peterborough looks good, but 'jumpy' between Whittlesey and Gold hill and also jumpy in the St Neots area.
Note: there are approximately 3,000 Flight radar ground stations compared to approx 200 ATOM stations so the chances that FR24 picks up your ADSB transmission is much higher because you are likely never to be far away from an FR24 station.
Flight on the 22nd shows similar big jumps.
However, flights in July show a good signal being picked up, so has a connector been disturbed or something else changed?

I'd be looking at the ADSB antenna / cabling installation, FR24 (and Vector) are indicating a possible range problem.

Deker.
Thanks Deker.

The transponder cable did get shortened and a new plug fitted on it post accident as the old cable was always too long (bent around the pod bag) and in fact it came off when I was dismantling the plane.  I am sure I checked there were no shorts when I put the new plug on it, but I'll check again.

Suspect some of the jumpiness on the FR24 track is the PAW GPS losing signal.   The GPS mouse trail prior to July was on the top of the pod, to the right of the front strut.  Post-accident reassembly it got installed on top of the base tube at the bottom of the front strut.  On the flight of the 22nd I noticed a couple of GPS dropouts and planned to relocate the GPS mouse,  so I'll do that first.    It doesn't explain a potentially poor range on ADS-B though.

Geoffrey

exfirepro

Re: Vector shows PAW but not ADS-B signals
« Reply #12 on: December 31, 2020, 01:01:01 pm »
That front strut is too close to the PAW antenna. I suspect it may be acting as a reflector and improving the signal to the left at the expense of the right.

Many microloghts and Gyros have the coms antenna on the top of the nose, as far forward as possible. Is that an option?

Hi Geoffrey / Ian,

Sorry, I’m playing catch-up on the Forum.

I agree, the PAW polar diagram appears to show significant obscuration to the front right, but with the antenna in its 'new' position as shown in the most recent photo, I would be surprised if the front strut alone would cause such a significant area of shadow to the right side of the plane - as the greater part the antenna is now above / in front of the strut. I must admit, however, that I'm at a loss to think what else in the plane would be obstructing your PAW signal to the front right to such a broad extent, so maybe there is more to this (as Ian suggests) than at first appears likely. The 'gap' might of course just have been poor line-of-sight to the Ground Station antenna(s) at whatever range and heading you were when being received by them. Blocking of your PAW signal to the right rear, however, will almost certainly have been due to a combination of the front strut, plus (to a varying degree, particularly bearing in mind that the receiving stations are predominantly below), the front fork and wheel assembly, battery, instruments in the panel, plus (presumably) your phone or tablet - as well as Pilot / Passenger / engine and rear suspension as you alluded to earlier (as well as potential line-of-sight issues to the Ground Station antenna(s)).

I was about to suggest moving your existing antenna to just inside the outer edge of the upper windscreen - as high up as you can manage, which would clear the immediate (close) obstructions, and help to reduce obstruction to the right rear due to Pilot, Passenger, Pylon and Engine, etc., but have just seen your recent post about dropping the wing for storage, which would make this awkward (though not impossible - it would just involve disconnecting the cable from the antenna before removing the upper screen).

And Yes Ian, it would be 'possible' to fit a PAW antenna externally on the upper front of the pod, but very difficult to align it vertically (if using a standard Rohan 'external antenna') and, as the front strut goes on down through to a bracket at the front of the base tube, it would still be right behind the antenna, so could actually make coverage to the rear worse. As you say, Geoffrey - worth checking results with Brian M first. :)

WRT fitting an external antenna further back below the pod, that's the option I have settled on after considerable trials. Mine is fitted just in front of the fuel tank with a flexible ground-plane on the inside (my Txpdr antenna is mounted through the rear skirt on a separate aluminium sheet ground plane, earthed to the base tube). I have now been using this setup for over a year, with excellent results, though from the attached diagram I still seem to be seeing some obscuration from the rear undercarriage and to the front by the front wheel and suspension, though I currently only have the one polar diagram from one single (approx 1hr 30) flight past 3 ATOM Ground Stations on Christmas Eve, two of which were at fairly long range (my most recent previous flight was well in excess of 30 days prior to the introduction of the Vector Tool due to the Scottish travel restrictions).

I did, however carry out a fairly short local flight immediately prior to the test flight shown, involving a 'circuit' of the area around my local airfield at up to about 5 miles range from the ground station, with several fairly tight 'orbits' at various points in the flight while still well away from the station (to ensure 360 degree visibility to the station antennas). I then checked the Vector track immediately after landing and prior to the main test flight. The initial report showed pretty effective 360 degree coverage, though of course with a maximum range of 5 miles, but unfortunately I omitted to take screenshots as I was pushed for time to get the main flight in before dark, so this is incorporated in the main report. In view of the relatively short flight and relatively long range from two of the 3 Ground stations reported during my main test flight, and my previous ‘good results’ from other evaluation tools, I suspect the 'gaps' in the Polar Diagram may be due to ground obscuration at or near the Ground Stations or simply my heading in relation to them during this single test flight rather than simply obscuration at the plane. I need to do some further testing once the travel restrictions are relaxed to confirm this.

If you do decide on the option to add a PAW antenna below the pod, I wouldn't worry about 'missing' aircraft above you. We did lots of testing for this in early PilotAware trials and found that it was almost impossible for a plane to approach from above (or vice versa with a top mounted antenna) without it being seen well before it got above us (or below as appropriate). IMO below is a much better option for external antennas, especially if you want to receive Ground Station uplinks reliably.

In closing, I’m not sure why your Vector search is bringing up your PAW results from your flight from 9th August - Vector is only 'supposed' to report on flights from the past 30 days (though I have seen a few flights listed on other ICAOs from ‘30 + a few’ days)..

WRT your ADSB issues, it definitely looks like a fault to me. Loss of GPS to the Txpdr - would prevent Mode-S/ES transmission, but would also affect PAW transmissions and would be reported as gaps on your Nav System and PilotAware Tracks, so relatively easy to check. Please let us know how you get on.
 

Best Regards

Peter
« Last Edit: January 01, 2021, 10:18:19 am by exfirepro »

Young_C

Re: Vector shows PAW but not ADS-B signals
« Reply #13 on: January 05, 2021, 01:48:48 pm »
Vector is an excellent function – well done PilotAware team, thanks  :D :D!

FYI attached are the plots from my RV-7 (external antennas under cockpit) from 5 flights in Nov-Dec last year. The first shows all EC and the second is just ADSB. Looking at the data overall there were 14154 contacts over the 5 days, but ADSB only had 2738 contacts on 4 out of these 5 days. I guess there wasn't much ADSB equipped traffic flying in the area on those days, however at least it confirmed that ADSB was being picked up with my PilotAware installation.

Chris Y
G-RVAH

Keithvinning

Re: Vector shows PAW but not ADS-B signals
« Reply #14 on: January 05, 2021, 02:22:48 pm »
Hi Chris

The PilotAware transmission polar diagram is stunning and shows a great installation well done.

When you say that this proves that you were picking up ADSB with your PilotAware installation, unfortunately, it does not. The polar diagram is of the ADSB transmission out of your aircraft and being picked up by the ground stations.

Regards

Keith