[Discuss-gnuradio] Using GMSK Mod to send digital data (e.g. an ASCII string)

[embyte]

Hello list, I would like to transmit some data using gnu-radio. My data 
is a binary representation of an ASCII string.

I wrote my own block that builds the frame (header, payload, CRC, 
trailer) as an array of 256 bytes (0s or 1s):

gr_make_io_signature(0, 0, 0)
gr_make_io_signature(1, 1, sizeof(char))

char *out = (char *) output_items[0];

[build the frame]

memcpy (out, frame, 256);
noutput_items = 256;

My question are:

1. Still I have to insert a "Packer Encoder"  between my code and the 
GMSK mod? If yes, with which parameters? The GMSK mod is configured with 
Samples/Sym=50 , BT=0.4.

2. Can someone explain me how to use the bitrate parameter? I mean, 
should I "sync" the output of my block with the modulator? If yes, how?

I tried to redirect the transmitted signal to a file, and use a receiver 
(that I know working), but without success. The parameters used in the 
receiver's GMSK demod are the same configured in the modulator.

Thanks!