Hi Dave,
Does this mean that if you have an ADSB equipped transponder already fed by an Altitude Encoder the barometric pressure sensor isn't needed - because it is only used if feeding data from pilotaware into a mode s transponder, or is the situation as below
In order for altitudes shown on Skydemon to be comparable with a received ADSB signal the pilotaware will require a barometric sensor (or the QNH updated manually in the web page)?
Complicated, isn't it
This is nothing to do with the Altitude you are transmitting through your transponder, it is about comparing
relative heights between yourself and surrounding traffic.
ADS-B contains the Pressure Altitude, so altitude based upon an altimiter setting of 1013.25mb.
In order to correctly compare to ADS-B altitude against our own altitude, we need to either
1. Adjust the GNSS altitude using the given QNH
2. Use our own Pressure Altitude
The heights of traffic passed to SD, RunwayHD etc are relative +/- heights to our own position, not absolute heights.
So in order to calculate those relative height differences, in the case of ADS-B, we compare to our Pressure Altitude
in the case of PilotAware we use our GNSS Altitude.
The Navtool simply receives a message indicating the relative traffic height.
I hope that is clear
Thx
Lee