Output of a file source in GRC

Hi all,

I connected a file source with a OFDM Mod block in GRC. File in the file
source is a .txt which contains 00000… (a sequence of zeroes).So could
anybody tell me what is the output bit stream that fed into OFDM Mod?
(if I choose Byte format)

File Source–>OFDM Mod

Thx!!

Best,
Jia