The differential data transmission method based on Nondirection Beacon(NDB) for the BD2 Global Navigation Satellite System(GNSS)was proposed.The DPSK signal's influences on the performance of airborne radio compass including bandwidth

direction finding and beacon recognition

were analyzed in detail.The characteristics of DPSK-based differential data transmission were compared under both the noise-free circumstance and the additive WGN(White Gaussian Noise) circumstance

and the corresponding conclusions were drawn explicitly.During the period of Morse codes transmission

the influences of Amplitude Modulation(AM) on the demodulation process and the Baud Error Rate(BER) of DPSK were also analyzed

and the synchronization between DPSK and the audio frequency signal was proposed to ameliorate the influences mentioned above.The simulation results are given that

the beacon identification function and the direction finding of the radio compass cannot be influenced by DPSK modulation

and the synchronization between DPSK and the audio frequency signal is an effective approach to overcome the AM's influences on the DPSK demodulation.