Maximum range on Vector for PAW vs ADS-B

[DavidIOW]

I have PAW Rosetta, with external aerials on the aircraft belly, and it works very well. More recently I have connected it to my Trig TT22 to provide ADS-B out (SIL/SDA 0). On Vector, the signal pattern seems to be good for both PAW and ADS-B, but the maximum range for the PAW signal seems higher than for the ADS-B. Does this make sense given that the Trig TT22 should have a much higher power output than PAW or can you not make such a simple comparison? While both results seem acceptable, I'm just wondering if this is indicating that the TT22 is not working optimally and needs investigation? A/C ID is 403B4C. Thanks for any feedback on this! David

[PaulSS]

ADSB is artificially restricted to 60kms to save drowning the world in red.

[PaulSS]

ATOM Stations are the same........AND why not to have a SkyEcho 

[PaulSS]

Another....because of the ridiculous 1995 picture posting size restrictions 

[PaulSS]

And the SE one.....more than 60 seconds later AND 1995 picture size restrictions 

[DavidIOW]

Thanks for the reply. Interesting about the 60km restriction. Is that a PAW Vector restriction of 60km for receiving signals or is my transponder somehow limiting its power output so it reaches no further than 60km(and how would it do that?)? Can you explain a bit more what the charts you posted are telling us? I thought the Atom stations only transmitted data on PAW frequency but received on everything?

[PaulSS]

The 60km restriction is only a limit on ADSB displayed on Vector. My ATOM station will see ADSB up to 200nm away but it will still only show a maximum of 60km on the Vector diagram. The same with your aircraft. It may be seen by an ATOM station 100km away but will still show as 60km being the max range on the Vector diagram.

The ATOM stations do transmit on PAW free and receive on PAW, Flarm and ADSB. The diagrams I showed were my ATOM station and the ranges it saw ADSB (artificially restricted to 60km), PAW and then CAP1391. It was to demonstrate the fact that, even though my ATOM station sees ADSB a LONG way away, it still only shows a max of 60kms.

[DavidIOW]

Thank you so much for the very helpful explanation! I am intrigued about your station as I am based at Sandown and have seen your symbol come up on the aircrew tracker site and have wondered where exactly you are?! I’m really impressed by the whole Atom network and now have the i-grid as well which has given us very good traffic info in several recent XCs. I’m just surprised by how many aircraft still don’t have anything at all telling people where they are in the sky! Devices like PAW and SE2 etc are so easy to use and install, (and in the aviation world are a relative bargain especially with the CAA grant) that it feels like they ought to be mandated in anything that gets airborne and likely to cause you damage if it hits you!!

[PaulSS]

Haha, I know you're at Sandown as I did the screenshots on my PAW for your aircraft's LAA PAW and ADSB 'evidence' 

I'm in Wellow, so get a pretty good view of the people nipping around the Needles. Sandown has its own ATOM station (even if Dan doesn't seem to know anything about it  ) and there's one at a farm along Military Road. That one is more for the paragliders along the Downs but is useful for transmitting their lightweight EC over the Grid. I think Bembridge seem to have taken theirs down but there's still very good coverage between the stations at Hayling Island, Thorney Island, Selsey and the IOW.

[DavidIOW]

Dear me, Paul! How could I be so dumb as to not connect you with that Atom station after we talked all about PAW when you kindly did that check for us?! Sorry about that and thanks for the great explanations of this issue. The transponder/ADS-B/PAW is working really well and seems to have helped us get some useful zone transits. It’s also great that my wife can now track us wherever we are and can see us coming back! Hope you have been enjoying some flying yourself in that beautiful aircraft of yours and that we’ll see you at the airfield some time. Maybe we could do some kind of EC promotion at the airfield to get more people using EC as many of the local flyers cannot be seen on anything which can be a bit scary when the air is busy!

[exfirepro]

Hi David,

As Paul has so eloquently explained, the ADSB transmission display is 'restricted' to a maximum range of 60Km to limit the amount of data we have to hold in the database to produce the diagrams. (This is also why we no longer report on Mode S transmissions as that was even more data hungry.)

Having looked at your Vector reports, I'd have no worries whatsoever about your transmission coverage on P3i or ADSB. Both are excellent examples of what can be achieved by the use of properly mounted external antennas. Well done!

Best Regards

Peter

[DavidIOW]

Thanks, Peter.

Good to know that you consider both of my transmission types to be working well! I'm all for shouting out to the world where I am! However, is there any way to determine how well the PAW-supplied ADS-B receiving aerial is working, other than by seeing what traffic comes up on my radar/SD view and hoping that it's a true representation of all the ADS-B traffic out there? eg can I compare what ADS-B traffic I 'see' in the cockpit, with what ADS-B traffic the Atom ground stations are seeing (which hopefully is everything)?

[exfirepro]

Hi again David,

All of the ADSB Traffic received by PilotAware is passed to your EFB unless you have deliberately restricted this in the’Horizontal Display Range’ and ‘Vertical Display Range’ settings in PilotAware / Configure / Positional Contacts Settings. We recommend that these are both left at the default ‘Display All’ and that you only set a vertical reporting restriction in your EFB (e.g. +/- 1000ft or whatever you are comfortable with). You don’t need to set a horizontal visual reporting range filter as this is limited automatically by the screen zoom level. There is a separate set of filters for controlling the reporting of ‘Bearingless’ Mode-S’ and ‘Mode-C’ Traffic if you have Bearingless Traffic Reporting Enabled in PilotAware and in your EFB (it’s off in both by default). MLAT (triangulated) Mode-S positions are displayed in the same manner as other ‘known-position’ traffic provided you have Mode-S/3D enabled in PilotAware.

If you want to check traffic received by PAW, you would need to compare the ‘PAW Traffic Screen’ against something like FlightRadar24 or one of the other public reporting sites, but be aware that these sites don’t always report traffic accurately. PilotAware reports all traffic unless you have the PilotAware Traffic Filters set other than default (when filtered traffic will show as greyed out on the Traffic Screen). Also be aware that the list of traffic shown at the bottom of the Traffic Screen (with ‘C xxxx codes’) is ‘under investigation’ as part of the ‘Mode-C’ identification process and usually proves to be one of the aircraft positively identified further up the chart rather than a ‘Pure Mode-C’ signal - after which the ‘Cxxxx’ entry is automatically filtered out.

In practice, if you are seeing 1090 traffic on screen, that part of PilotAware is working properly and to its full potential (assuming you have Bearingless and Mode-S/3D enabled and the filters sufficiently wide open). It either works very well (99.999%+ of the time), or not at all - in which case we need to look at the 1090 antenna, cable or the SDR.

Hope this helps

Regards

Peter

[PaulSS]

can I compare what ADS-B traffic I 'see' in the cockpit, with what ADS-B traffic the Atom ground stations are seeing (which hopefully is everything)?

I addition to what Peter has said, comparing what an ATOM station sees and what you might see is not really a fair comparison. For instance, I might not see a low level aircraft south of the Isle Of Wight because the Downs get in the way of his transmission to my antenna. You, on the other hand might see him, as you nip along the South Coast at 1500'. You are now 'better' than my ATOM station.

Likewise, I have an 11dB antenna on top of my house, while you probably have a 5dB antenna in your aircraft. In theory I would see many more contacts than you and you would feel very disappointed (since I am now 'better' than you), if comparing numbers and distances, whereas, in reality, your aircraft is seeing all the ADSB transmitters within XX NMs of you and allowing you to avoid bumping into them.

I can see you're trying to compare your maximum with a theoretical maximum but I don't think using ATOM stations is the way to go and, quite frankly, if you're seeing all the stuff that's anywhere near you then it is a pretty pointless exercise anyway. It doesn't matter that you can't see BA 123 at 350nm away but I can.

[DavidIOW]

Peter and Paul. Thank you both for the comprehensive replies which help me to understand the whole system better. What you have said explains what I am seeing on Vector and gives me confidence that I should be well visible to other suitably equipped aircraft and likewise I am able to see them. I’m also reassured that my ADS-B out is working very well! On a local flight today I was easily able to see various aircraft at similar heights come up on SD and then be able to spot them for real. PAW really enhances the effectiveness of the normal scan but of course does not replace it.  I hope you will continue to encourage everyone to be transmitting something so that more aircraft become more visible to others. The PAW system is so simple to install and use, yet is so effective! Thanks!