You are probably transmitting positionless weather reports because your selected station APRS symbol isn't a weather station symbol. According to the APRS protocol specification, course and speed are only interpreted as applying to wind for weather stations (which are normally fixed position and therefore always have a self-speed of zero); for all other stations, course and speed are assumed to apply to the motion of the station itself. So, to avoid misinterpretation, if your station isn't identified as a weather station, YAAC transmits a position report with your symbol, position, and the course and speed of the radio, followed by a positionless weather report with all the weather parameters in it. Since both packets have the same callsign-SSID, a receiving station should be smart enough to match them together.

Hope that explains why you're transmitting two packets each beacon time.

Note this little quirk also allows for the possibility of mobile weather stations (i.e., storm chasers), but such stations have to do the vector math to convert vehicle-relative air velocity into wind velocity (prior to packet transmission) by vector-subtracting the vehicle ground velocity and accounting for the vehicle course rotating the bearing reference of the wind vane.

Andrew, KA2DDO

author of YAAC