Gillham Code

properties
Hamming distance	1
Steady	No

The Gillham code is a Gray code with exactly twelve binary digits , which is used in aviation for transponders for coding and for the automatic transmission of the barometric height information of the flight object to ground stations. The code is laid down in its structure by the Federal Aviation Administration (FAA).

The Gillham code, like every Gray code, is a “single step code”. This means that in the binary representation of the height information, adjacent height levels only differ in one single binary digit. If more than one digit has changed during the transfer, the value at the receiver can be discarded, as the last value received was then incorrect.

In aviation, altitude is traditionally given in the outdated unit of length feet (ft), where one foot corresponds to 0.3048 m. The transmitted values ​​range from −365.76 m to +38618.16 m in steps of 30.48 m. The coding is carried out according to the following scheme:

Gillham Code	Height [m]	Height [ft]
000000000001	−365.76	−1200
000000000011	−335.28	−1100
000000000010	−304.8	−1000
000000000110	−274.32	−900
000000000100	−243.84	−800
000000001100	−213.36	−700
000000001110	−182.88	−600
000000001010	−152.4	−500
000000001011	−121.92	−400
000000001001	−91.44	−300
000000011001	−60.96	−200
000000011011	−30.48	−100
000000011010	0	0
000000011110	30.48	100
000000011100	60.96	200
000000010100	91.44	300
000000010110	121.92	400
000000010010	152.4	500
000000010011	182.88	600
000000010001	213.36	700
000000110001	243.84	800
000000110011	274.32	900
000000110010	304.8	1000
000000110110	335.28	1100
000000110100	365.76	1200
...	...	...

Individual evidence

1. ↑ radartutorial.eu
2. ↑ scribd.com  ( page no longer available , search in web archives )  Info: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice.