SK01 is the former digital flavor of the Cuban DGI. Replaced by HM01 in 2012.

SK01 transmitted in one hour schedules, sending a single computer file with an 8-digit name and the .TXT file extension. The file was transmitted every 5 minutes, with only silence in between. The contents were mostly binary-coded decimal.

The mode used by SK01 was RDFT (short for Redundant Digital File Transfer), an off-the-shelf open source system initially intended for amateur radio use. The DGI used DIGTRX to transmit and receive it.

History

SK01 appeared in its latest form in late 2007. However, during the year before, the DGI had run experimental transmissions using the amateur modes BPSK31, QPSK31, and BPSK220F, sending 5-digit group messages similar to V02a and M08a.

In early 2007, the format of PSK transmissions was as follows:^[1]

1. "11111" and the current date in the format DD/MM/YYYY (all repeated thrice)
2. 5-digit message header repeated five times, then 150 5-digit groups
3. "+ + +"
4. "22222" and the current date in the format DD/MM/YYYY (all repeated thrice)
5. 5-digit message header repeated five times, then 150 5-digit groups (both different than the previous message)
6. "+ + +"
7. "33333" and the current date in the format DD/MM/YYYY (all repeated thrice)
8. 5-digit message header repeated five times, then 150 5-digit groups (both different than the previous messages)
9. "+ + +"

In mid-2007, the format was changed to the following:^[2]

1. "11111 11111 11111 11111 11111 11111 11111 11111 11111 11111"
2. 5-digit message header repeated ten times
3. 150 5-digit groups
4. "22222 22222 22222 22222 22222 22222 22222 22222 22222 22222"
5. Repeat all of the above thrice, but with different headers and messages

References

1. Ary Boender, Numbers & Oddities #113 (January 2007) [accessed December 21st, 2014]
2. Ary Boender, Numbers & Oddities #115 (March 2007) [accessed December 21st, 2014]