For high precision navigation by means of carrier phase DGPS two aspects are from particular importance: first, the correct and fast resolution of the ambiguities and second, the detection of some signal problems, which can lead to unacceptable errors in the position. Actually, these two aspects are very close related. The paper describes how the efficiency of our OTF algorithm was improved by taking into account the quality of the used observations. The data quality depends not only on the type of the used receiver, but also on the environment of the observations. Field data are analyzed to show the distortion of the measurements caused by interferences and particularly by changes in the dynamics of a moving receiver. These distortions often proved to be the reason for ambiguity fixing inefficiency. To demonstrate the dependence of the quality of the observations on the receiver performance, measurements with TRIMBLE (SSE & SSi) and Leica (SR 299 and SR 399) receivers in parallel are analyzed