Sergio,

you are correct indicating that "code balance" is crucial if you are directly modulating the rf. Using a non-balanced code (i.e. direct ANSI Serial) the error accumulates until it appears as a DC component that "distorts" the intended waveform.

Your suggestion of Manchester is a good one however you can code balance the ANSI Serial data by selecting only balanced code patterns (even 1's and 0's) and using them to "encode" your intended data pattern.

i haven't used the BIM but i have used the Linx devices which look physically similar (from advertisments) These devices require code balance to propagate even small data packets 8-16 bytes with integrity otherwise the error rate is very large.

regards,
p