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The characteristics of BDS (BeiDou System) observables were analyzed with 30 days of observables collected at five stations distributed in Asia-Pacific area.Signal-to-noise ratio,phase-minus-code combination and MW(Melbourne-Wübbena) combination of BDS observables were investigated.Kalman filtering was employed to smooth the time series of MW combinations.The signal-to-noise ratios are different from satellite to satellite,while the differences among different frequencies are marginal.Diurnal fluctuations can be seen from the time series of phase-minus-code combinations,and they probably reflect the daily variations of ionospheric effects.Typical standard deviations of MW combination for GEO satellites are between 0.27 m and 0.37 m,and those for IGSO satellites are around 0.42 m.Fractional parts of mean values of MW combination for different passes of IGSO satellites remain almost constant,while similar behavior is not shown in the case of BDS MEO satellites.For GEO satellites,daily fluctuations can be seen in the time series of MW combinations.Due to these different behaviors,the strategy of wide-lane FCB estimation may depend on the type of satellite,rather than simply averaging MW combinations for all of them.