Trouble with 2KM RF Link modules

I purchased the 2KM RF Link encoder/decoder pair (WLS102B5B) to provide wireless communications between two Arduinos. Unfortunately, it seems that whenever I set a data line High on the transmitter, it doesn’t reliably lead to a high on the corresponding receiver pin unless I leave the transmitter pin high for about a second. The link seems even less reliable if I use multiple data lines at once. Am I missing something about how to implement these devices? I haven’t been able to find any documentation on the modules themselves (outside of the datasheets for the encoder/decoder chips). I’ve also tried simply sending/receiving serial messages between the Arduinos with the modules but that doesn’t work either even at low data rates.

You probably need to use Manchester code. Try sending a stream of ‘U’ characters, you should be able to receive them because of the alternating 1s and 0s.