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
1110010011110111 Start of transmission
1110010010111011 End of transmission
1110010101001100 1st digit of the ID follows
1110010101111001 2nd digit of the ID follows
1110010101101010 3rd digit of the ID follows
1110010100010011 4th digit of the ID follows
1110010011000010 Space
1110011100101100 0
1110011100011001 1
1110011100001010 2
1110011101110011 3
1110011101100000 4
1110011101010101 5
1110011101000110 6
1110011110100111 7
1110011110110100 8
1110011110000001 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:

1110010011000010
1110010011000010
1110010001111100
1110010011100010
1110010001011010
1110010011000010
1110010000110000
1110010011000010
1110010000010110
1110010011000010
1110010011100100
1110010011110111
1110010010101000

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 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.

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

Note that a variant of this mode exists where the characters 0 1 2 3 4 5 6 7 8 9 are given the respective bit sequences of characters 5 9 1 6 2 8 4 0 3 7, but only for the actual message groups.

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