Sorry for my bad english. Is there a way to analyze the data signal from an RX868. The problem is that the output signal is 0V/3V.
mfg santje243
The ouput signals of your FEZ is also TTL 3.3V, so connecting it to the RX868 module should be easy !
If you want to “analyse” data from an RX868, you may need a logic analyser, such as the ones described in this thread : http://www.tinyclr.com/forum/1/3104/
Have fun 
What are you trying to analyze? There are already a lot of protocols documented on the internet including BidCos and FS20 from ELV.
Sorry analyze is not the right word. I will read the data and extract the housecode, adress and so on. When i
connect data to a digitalinterruptpin the interrupt will never execute. I think the 3V level is to low. will i need a levelshifter or is there a way without it.
I don’t think so. 3V is well enough to trigger the datapin. Please show your code, there must me a problem ! 
When you manualy connect a wire/push button to your datapin with a 3V3 signal, does your interrupt triggers ?
I don’t think an interrupt is the way to go. I would go for the PinCapture function (see GHI library docs in the Hardware namespace).
And yes, showing your code does help in getting correct responses (please use the code button when posting your code).
Eric,
Sometimes the interrupt is still the best way to go : pincapture is blocking, and you never know when the transmission is going to start… If the speed of the transmission is low enough 
This IR code shows a great example of capturing (slow) dataflow with interrupt: http://code.tinyclr.com/project/267/infrared-sender-and-receiver/
I have seen this example. When i am back at home i check out the example and whether the Interrupt triggers at 3V3.