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To create a number convert it from decimal to binary 3456789 for example is 1101001011111100010101 in binary. Then reverse bit order 1010100011111101001011

Then you need to add the "ghost bits" (called that because we had no idea what they do, they are NOT checksum, but rather counters for the unknown status packeges) The ghost bits (x) are placed on every 4th position so you take one ghost bit then 3 of your number bits and fill out 0 in the end x101x010x001x111x110x100x101x1(00)

The ghost bits can be all 0 for now. Now run the numbers through the encoding algorithm. The encoding algorithm is a checksum in sort, it works in a way that if you get a error in the signal it can tell what the next bit should be and fix it. 11 and 00 is a 0, 01 and 10 is a 1.

Running through the encoding algorithm we calculate the sum of certain bits with the formula (n-0)+(n-1)+(n-2)+(n-3)+(n-9)+(n-14)+(n-15)+(n-17)+(n-18)+(n-19)+(n-21)+(n-22)+(n-23) , if it is even or odd we get a 1 or 0. This gets the first bit in the 2 bit pair signal that we send. the second bit is opposite of the first bit from bit n-1.

(0)1010010000101110110010001010100 first bit is 0+0+0+0....+0 because we count non existing bits as 0. and then the data of n-1 is 0 so we get 00.

0(1)010010000101110110010001010100 Second pair is 1+0+0+0.... so we get a 1, and data of n-1 is 0 so for a 0 in data we get the same as the first bit so the second pair is 11

01(0)10010000101110110010001010100 third pair is 0+1+0+0...+0 even so we get 1, and data of n-1 is 1 so we get second bit the opposite as the first so we get 10

and so on...

the result is: 00111000011100101111111101001010010010100000010011 0001110100010011001111110000 but we have to cut the first pair away to get the correct result 11100001110010111111110100101001001010000001001100 01110100010011001111110000

then add the pre-amble. 1111100100010110 in front and you have the id number to send.

BUT this only work on old decoders. As you might have noticed if you try and get data from a transponder it sends more packages apart from the id number. And these packages we have no clue what they are apart from that the ghost bit is counting them with a 3bit-counter so there was 6 or 7 of them if I remember correct. New decoders seems to want this information also for a transponder to work correctly.