[RC232] We are trying to configure our modems RC2500HP 201545H to use them at a data rate of 250kbit/s, following the datasheet rev 1.22. However the communication fails at this RF rate. Back to 100 kbit/s the communication is works again.

Assuming this is RC2500HP-RC232, this has a max datarate on RF of 100kb/s.
This is given in first page of datasheet.

I know that the configuration information in datasheet give info on how to setup 250kb/s, which can be misleading.

Last Update: August 8, 2017