The same function 0 address was just rebroadcast again from the tower. Notice this time however that it has a different LRC and CRC than it did four hours ago.
14:56:47 LJ-1200 FAIL CRC FUNCTION [0] ADDRESS [55761E4] VRC [DD] LRC [EF] CRC [1F2D] 01010101000011111011101111110111000000100111100001101110101010100001111100101101
This was the third message in the data burst which consisted of nine messages.
I wonder why the tower would send a different LRC and CRC when the function code and address remain unchanged? I wonder whether LRC (computer control) is somehow incorporated into the CRC at least for function code 0 messages?
Notice the change in the bits between the first message and the second message. Four different bits changed from 0 to 1.
Shawn
Shawn, you may be seeing overlapping messages. Notice how the bit revs and sync pattern appears toward the end of the message.
sdrtrunk uses a continuous sync pattern matcher and will start a message assembler each time it detects the sync pattern.. I do this so that if the first sync pattern detect is a false trigger, then I won't miss the second (real) sync detect. You then have to rely on the CRC to sort the good from the bad.
Denny