Packet Encoder usage

I want to send packets from the USRP to a tranciever chip (specifically
the CC1101, made by TI). I know the packet structure that it expects,
and I know the frequency and data rate it expects. I’d like to simply
transmit the GFSK modulated version of those packets. I threw together a
small flow graph in GRC, but I wasn’t sure what the input of the Packet
Encoder block wanted. Can I give it a file source that’s just got the
binary version of my packet? More generally, has any work been done with
the SimplciTi protocol or the CC1101 and the USRP/GNU Radio before?