From the PilotAware website:
PilotAware is a minimal cost system in which the Hardware and RF Protocol is made public. The System is capable of Receiving ADS-B, Transmitting NMEA messages to a transponder capable of providing ADS-B out.
In the case of Aircraft not equipped with a transponder, an additional transceiver operating in the 868Mhz License free frequency provides additional positioning information using the Open P3I protocol to surrounding traffic.
PilotAware can support interfaces to
- ADS-B (in)
- ADS-B (out)
- P3I (in/out range 25km)
- RS232 Out (NMEA Sentences at 4800 baud)
- RS232 Out (NMEA+ADSB+P3I Sentences at 57600 baud)
- WiFi Software AP (NMEA+ADSB+P3I)
The parts are readily available modules. There are some 3 or 4 wires to solder, the rest just plugs together. I think the weight would be less than 200 grams. I have seen a figure somewhere but can't locate it at the moment. The parts I have bought in preparation seem to indicate a very light weight for the project indeed.
Take a look at the Construction Guide under Hardware here:
Introduction - Home
I hope that's useful.