OGN-R uplink typical range

[Young_C]

Hi,
I'm curious about the uplink range also and had a recent discussion about it on the RVSqn forum.

I used the new Vector tool which showed good 360deg downlink coverage out to between 60-80km. I can also typically see contacts out to 96km on the PAW radar screen in my aircraft (see attached screen shot).

Based on this I had assumed that I was getting good coverage of both:
A) aircraft to aircraft detection (PAW and ADSB traffic) and
B) ground to aircraft detection (FLARM and MLAT) from ATOM uplink.

However if the uplink range is poor / variable then I could be missing B) traffic completely and my PAW radar screen would only be showing me traffic from A)?
Is there any way of determining this, either in-flight or afterwards by analysing track files?

Obviously having a radar screen full of contacts is a step forward from not having any EC, however it would be useful to know for example if I'm missing glider traffic. 

Thanks,
Chris.

[buzz53]

However if the uplink range is poor / variable then I could be missing B) traffic completely and my PAW radar screen would only be showing me traffic from A)?
Is there any way of determining this, either in-flight or afterwards by analysing track files?

Hi Chris,

That is the absolute nub of this rather protracted bit of thread. If you download your track file from your PAW, and upload it to this tool:

https://aircrew.co.uk/playback/

then from the comfort and safety of your armchair, rather than peering at your screen in flight, you can see exactly what went on. You will see when you received beacons sent from each of the groundstations (about every 15 seconds unless the GSTN is saturated with other traffic). My caveat (also on the RVSQN) was that with the PAW software in use back in August, these GSTN beacons were filtered out from the track file the same as aircraft, so if you were not careful about how you set the filters (assuming you use them at all) then you might conclude the uplink range was less than it really was. Following that post I realised that the PAW track file now uses a different method of logging the beacons, so what I said about filtering may no longer be true. I'm hoping Lee will answer one way or the other to clear this up, since I can't check it experimentally at the moment for obvious reasons.

Alan

[Young_C]

Thanks Alan,
I reviewed one of my flights from June 2020 using the Aircrew playback tool. I could see all the traffic but not the groundstations, but I'm not sure whether they were being filtered out or I wasn't using the tool correctly.

Most of the traffic seemed to be ADSB which presumably was received directly aircraft to aircraft. I did spot a glider which had "G P U" and PilotAware and Uplink were shown when I hovered over the P and U. Does this mean that its position was coming via uplink or directly aircraft to aircraft from its PilotAware unit? Apologies if this is a stupid question but I'm not familiar with the Aircrew tool.

Any hints tips or instructions would be gratefully received.

Best Regards,
Chris.

[buzz53]

Chris, I would say those GPU targets were uplinked. Did you see any groundstation tower symbols in the replay? I think a tower only appear on the map if at least one beacon has been received from it during at some point during the flight. If so did none of them display green rings around the tower as you got near? This happens for a short time after each beacon packet is received.

I'd be keen to haev a look if you want. You can make your flight public on the replay site and PM me the link (or post it here) or better still just PM me me the file.

Alan

[Young_C]

I have uploaded the flight and made it public. The glider I spotted with GPU is at 09:27 north of my track near Husband's Bosworth.

Here is the link:
https://aircrew.co.uk/playback/458ef337

[buzz53]

Chris, I'll have a better look at your track later today when I'm on the train, but I can see you had several uplinked targets apart from the glider, but oddly no groundstations displayed. I wonder if you did not have the "Display Ground Stations" box ticked in the PAW configuration?
Alan

[Young_C]

Thanks Alan,
I will need to check my PAW settings next time I'm at the aircraft, I cannot recall changing this setting and the instruction manual does not state what the default setting is for this.

Studying the flight on the Aircrew tool again, I can see most of the traffic was ACSB, which I think is a straight ADSB reception a/c to a/c. I was getting good range on these targets out to ~80nm.

You are correct that there were a few with "U" so I was receiving uplinked traffic. However I cannot tell whether there were so few because the uplink range / coverage was poor or whether there was not much traffic around on this day in this category. I'm suspecting the former since these targets were quite short range and very inconsistent appearing and disappearing often.
The few that I saw were:
- ACSPUM, i.e. Mode-S detected directly with MLAT data being Uplinked
- ACSPU, could be position from PilotAware unit or maybe FLARM uplinked?
- PU, although type is shown as glider, according to the manual this is an OGN-R station uplinked via PilotAware which makes sense since it doesn't move?

I could not see any "F"s for FLARM, but perhaps FLARM position source but uplinked via PilotAware would be displayed ACSPU?

Regards,
Chris.

[Deker]

Hi Young,

I've looked at the linked playback file and clicked all the aircraft that were uplink or Mlat.
This shows their traces in the horizontal view on aircrew/playback and gives an approximation of uplink 'continuity'.

I'm guessing you had intermittent uplink from Turweston, Husbos and other(s) near peterborough.
Deker

[steveu]

So would it be worth extending this by getting the maintainers of the mentioned ground stations to look at Vector analysis for PAW for all aircraft?

[Young_C]

Many thanks Deker - that's really helpful 

I guess there may be a problem with my 869.5MHz reception since three different ground transmitter uplinks were all being received intermittently?
The 1090MHz reception seems to be good since I'm getting good range and few dropouts from ADS-B targets.

Now that I'm learning what to look for, I will study a few of my other flights to check whether the problem is consistent.

Best Regards,
Chris.

[Deker]

It's also worth knowing that the OGN base station software has been updated several times since July which may help with this issue.
There was a theory floated that an uplink from one station could be stomped on by another therefore only a garble uplink was being received in the air. I think there is now some sort of uplink scheduling between ground stations to help prevent this, so may not be all down to your installation???
I'm still trying to get some flights in myself to do some more testing - not been easy!

Deker

[Young_C]

Hi,
I've analysed a couple more of my flights (ideal way to spend my time on a cold, foggy, Saturday in lockdown  )

See attached:
Slide 1 - Bidford to Wadswick 31-Aug-2020.
Slide 2 - Sandown to Bidford 16-Oct-2020.

Both flights show much better range and consistency receiving ADS-B contacts. Once again there were far more ADS-B contacts than uplinked contacts.
Slide 1 - the uplinked contacts were very inconsistent throughout the flight.
Slide 2 - the uplinked contacts were consistent around Basingstoke with gliders detected and staying in contact, however further north near Bicester I only received intermittent glider contacts (although they were further away from my track)

I'm not sure what to conclude, it was reassuring to see that on the later flight I did get some good uplink performance maybe due to OGN base station software improvements or perhaps the transmitter near Basingstoke was better or I was closer to it.

Anyway I will do further investigation next time I fly.
Thanks for all the assistance so far.
Regards,
Chris.

[Admin]

Hi Chris

I briefly looked at your info, and I would say you were receiving the traffic as peripheral detection

What does this mean I hear you say.

You will only trigger an uplink IF the traffic is within 10km and +/-5000ft of your position

You will receive an uplink IF ANY traffic trigger is activated by any PAW emitter.

So Imagine you are 11km from a Glider X, but another (PAW) aircraft is 9km from Glider X
this will trigger a rebroadcast of Glider X which you will see via peripheral detection
If the other PAW aircraft now moves 10.1km from Glider X - it will no longer be rebroadcast.

This can appear to be intermittent, but this is in fact by design.

Remember you will only trigger aircraft when they are within 10km of you and actually, the full trigger set which have to be met
1. within 10km (horizontally) of a PAW Emitter
2. within 5000ft (vertically) of a PAW Emitter
3. not stationary

thx
Lee

[Young_C]

Thanks Lee, that's good info for me since I wasn't familiar with this peripheral detection functionality.

It also probably explains why I don't see many uplinked contacts if they are only received when within 10km. Also considering that I was flying during the pandemic when there was much less traffic anyway.


Regards,
Chris.

[Admin]

It also probably explains why I don't see many uplinked contacts if they are only received when within 10km.

Hi Chris
Just to be absolutely clear, 10km is not a receive constraint, it is a trigger constraint
Thx
Lee