In theory, yes this would be possible, but it’s not just a case of plugging in a second dongle, the software would need to be specifically configured to deal with this and there are potential issues with power draw from the Pi if ‘standard’ dongles are used.
In practice, this is not really necessary as this side of PAW is dealing with relatively high power signals from high power transponders / ADSB, both of which can be easily received while the aircraft is a long way off and well before it gets in a position where screening becomes an issue.
Best advice is to position the 1090 antenna where it gets the best view to the front of the aircraft and rely on reception at range. Remember, this antenna can be shortened to fit on the coaming (see link below), or can be fitted to the canopy (upside down) or an alternative antenna fitted outside the aircraft instead. Remember to keep the antennas as near vertical as possible.
As the 1090MHz side is receive only, you
could fit 2 antennas using a combiner, but these are pretty expensive, so it’s doubtful if this would be worth while.
http://forum.pilotaware.com/index.php/topic,438.msg5661.html#msg5661Similar positioning advice applies re the P3i antenna, but this is if anything more critical as the transmitters are only running 500mW (1/2 a Watt), compared to transponders at 100 Watts+ and combiners are not an option due to legal power restrictions in the 869MHz band.
Have you seen the Antenna Installation Document on
www.pilotaware.com ? See here...
http://www.pilotaware.com/wp-content/uploads/2016/10/PilotAware-Antennas.pdfRegards
Peter
