Taken from Mark5B System User's Manual (9 June 2006) Section 5.
Data on disk is divided into equal-length disk frames (DF). Each DF has a header of 4 32-bit words followed by 2500 32-bit words of data (10000 bytes). The DF boundary is aligned with the UT second tick.
|Word 0||Synchronization word (0xABADDEED)|
|Word 1||Bits 31-16: User specifed|
|Bit 15: T - tvg data (test data if set)|
|Bits 14-0: DF # within second|
|Word 2-3||VLBA BCD Time code and 16 bit CRC|
|Sync word (32 bit)|
|User-specifed (16 bits)||T||Frame# within second (starting at 0)|
|VLBA BCD Time code word 1 ('JJJSSSSS')|
|VLBA BCD Time code word 2 (16 bit) ('.SSSS')||CRC 16 bit|
Raw VLBI data is packed within a 32 bit word, with the earliest time sample corresponding to the least significant bits .