G. Laroche Web site 
Group RDS : 4 version A

The group 4A is used to transmit the hour and the date.
If this group is used, hours and date have to correspond exactly at the hour " Universal Time Coordinate " UTC + local offset. Otherwise the data must be positioned in 0.
When this group is used, it must be transmitted every minutes. The Clock time group is inserted so that the minute edge will occur within ± 0.1 seconds of the end of the Clock time group.
Hours and date are transmitted by using 34 bits, Assemble available data sets (part1,2 and 3) to form a block of 37 bits, 3 spare bits are used to complet the part 3.
b4  b3  b2  b1  b0  b15  b14  b13  b12  b11  b10  b9  b8  b7  b6  b5  b4  b3  b2  b1  b0  b15  b14  b13  b12  b11  b10  b9  b8  b7  b6  b5  b4  b3  b2  b1  b0 
spare bits


d16  d15  d14  d13  d12  d11  d10  d9  d8  d7  d6  d5  d4  d3  d2  d1  d0  h4  h3  h2  h1  h0  m5  m4  m3  m2  m1  m0  +/  o4  o3  o2  o1  o0 
Modified Julian Date : The date of day is coded on 17 bits to form a number from 0 to 99999 allowing to determine the day, the month and the year, as well as the daytime of the week, the number of the week and the number of the year since 1900. (See secondary G of file rbds1998.pdf for details of conversion funtions).
Hour : The hours are coded by a binary value not signed on 5 bits and being able to vary from 0 to 23.
Minute : The
minutes are coded by a binary value not signed on 6 bits and being able to
vary from 0 to 59.
Local time offset : the
offset is a multiple of half hour to vary of12h in +12h.
The sign +/is positioned in "0" for a positive offset and "1"
for a negative offset..