Author Topic: Altitude transmitted by PAW is on 1013 or the "correct" one?  (Read 482 times)

a.alexeev.p

Altitude transmitted by PAW is on 1013 or the "correct" one?
« on: January 19, 2022, 05:15:03 pm »
Hi,

It is commonly known that normal transponders transmit their BARO altitude on 1013 and then ATC does all the necessary conversion. Question - when PAW transmits it's position and altitude does it also do it based on 1013 BARO? Or does it transmit the actual altitude estimated by the device? The reason why I am asking as I flew on a 1022 QNH day and a colleague of mine was watching me on a plane tracking app. To our surprise the altitude we saw was spot on, which made me think PAW transmitted "correct altitude" and not on 1013. Is that right?

Admin

Re: Altitude transmitted by PAW is on 1013 or the "correct" one?
« Reply #1 on: January 19, 2022, 08:03:42 pm »
PilotAware emits gps altitude not barometric

Thx
Lee

a.alexeev.p

Re: Altitude transmitted by PAW is on 1013 or the "correct" one?
« Reply #2 on: January 20, 2022, 02:22:43 pm »
Hi Lee! Thank you for your reply. That is understood, but makes me wonder then how does it work in case of the OGN rebroadcast?

Say, I am receiving OGN rebroadcast about two aircraft 1) with PAW onboard 2) With ADS-B OUT or even Mode S MLAT. Does it mean that for 1 I will receive rebroadcast of the GPS altitude; and for 2 of the Pressure Altitude? Or are the two somehow brought together to the same datum at some point?

Or when another Aircraft (say ADS-B out) is detected by me directly and transmits PA, does that mean their transmitted altitude is compared against PAW internal Pressure Altitude (which I do not see)?

Admin

Re: Altitude transmitted by PAW is on 1013 or the "correct" one?
« Reply #3 on: January 21, 2022, 01:05:55 pm »
ATOM will only rebroadcast
- FLARM and MLAT/Mode-S/3D

PilotAware and ADSB are received directly

The ATOM station does not rebroadcast height information for MLAT/Mode-S/3D
That height information is received directly on the Rosetta Mode-S receiver, and compared against the local barometric

thx
Lee

a.alexeev.p

Re: Altitude transmitted by PAW is on 1013 or the "correct" one?
« Reply #4 on: January 21, 2022, 01:24:10 pm »
oooh! Now I see. So last thing just to be sure - when PAW decides about making or not making Audio Alert or say when I see other traffic relative altitude in Skydemon - that one is though comparing received Pressure Altitude to the Pressure Altitude (not GPS altitude) measured by the PAW unit?

exfirepro

Re: Altitude transmitted by PAW is on 1013 or the "correct" one?
« Reply #5 on: January 21, 2022, 11:08:46 pm »
Alex,

What Lee has explained is that the software in PAW is clever enough to know whether it is comparing altitude with a Mode C or Mode S transponder, an MLAT report originally generated from a transponder, or ADSB (whether DF17 from a transponder or DF18 from a SkyEcho) - in which case it calculates relative altitude using its inbuilt barometric cell, - or with another PilotAware or Flarm transmitter - in which case it uses GPS altitude.

In all cases it calculates the correct relative altitude, which is then passed to the EFB and displayed.

Hope this helps clarify the position.

Regards

Peter

a.alexeev.p

Re: Altitude transmitted by PAW is on 1013 or the "correct" one?
« Reply #6 on: January 21, 2022, 11:44:17 pm »
thank you so  much !! all clear now