priyom.org

Protocol

F11 utilizes a proprietary synchronous BFSK modem, set at the speed of 100 bd, and the shift of 620 Hz. The space frequency is at +1920 Hz, while the mark is at +1310 Hz. Each character is represented by a 16-bit sequence:

Sequence Character
1100100111101111 Start of transmission
1100100101110111 End of transmission
1100101010011001 1st digit of the ID follows
1100101011110011 2nd digit of the ID follows
1100101011010101 3rd digit of the ID follows
1100101000100111 4th digit of the ID follows
1100100110000101 Space
1100111001011001 0
1100111000110011 1
1100111000010101 2
1100111011100111 3
1100111011000001 4
1100111010101011 5
1100111010001101 6
1100111101001111 7
1100111101101001 8
1100111100000011 9

Each broadcast begins with approximately 1,135 zero bits, and then the character sequence "010", followed by the start of transmission character sent 8 times. Right afterwards, the 4-digit schedule ID is sent five times, each digit preceded by the appropriate Nth digit of the ID follows character. Then the following fixed 13-character sequence is sent:

1100100110000101
1100100110000101
1100100011111001
1100100111000101
1100100010110101
1100100110000101
1100100001100001
1100100110000101
1100100000101101
1100100110000101
1100100111001001
1100100111101111
1100100101010001

Then the transfer of the message groups begins. The messages are 5-digit groups separated by a single space.

Traffic that consists of the group "00000" repeated ten times is a null message.

Actual messages usually begin and end with the groups "88888 88888", and at the end the group count is sent twice, including the four "88888" groups, as 5-digit groups, padded with zeroes on the left. Sometimes, typically on longer messages, "88888 88888" might be omitted.

Broadcast ends with the end of transmission character sent 20 times.

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