Roger, tks for the info.
I have the IAS pitot tube from WEA, but in fact it is a Stephan Merz (SM-Modellbau http://www.sm-modellbau.de/shop/index.php) unit.
It might be a calibration problem.

I have the Eagle tree Pitot unit as well, might test it, as well as an JetCat Pitot Tube.

In order to get the WEA unit working (plus reliable audio output) I had to invest in a MUXBox, as I already have a GPS occupying the SCU slot. Plus another transmitter plus a DV4, as I was using DV3's. I think I did enough, now it's time for WEA to solve this problem and not let me buy yet another interface....

I am getting a bit of fed up with all kinds of suppliers who promise the world with telemetry, but in the end cannot deliver a decent working system. How many vario manufacturers did not promise that an IAS probe was imminent..

Here is a screen shot of one flight which contains several tug flights. The red line is the IAS, the green line GPS speed and blue is altitude. See how the red line stops at a certain value, from other data I know this is around 62 KM/h