Tnx fr the reply's! I contacted support at oss and it turned out that oss3991h didn't support full duplex. They suggested to download oss398f that should support full-duplex mode. It worked! I have to use 5000KHz AD and DA. At higher sample speeds the output isn't readably Planned is that oss4xxx will support full duplex again. 73 Rob PE1ITRLINRADDARNIL