... én ezt gugliztam :-)

 

"F2D: frequency shift keyed audio tone, data packet. Packet Radio."

http://en.wikipedia.org/wiki/Types_of_radio_emissions

 

"F2D:  Data transmission by frequency modulation of a radio frequency carrier with an audio frequency FSK subcarrier. Often called AFSK/FM."

http://www.ac6v.com/modcodes.htm

 

- Adott esetben jelenthet  szelektív hívót is.