4
1.2.3. Transmission Mode
According to M.625-3 of ITU-R Recommendations, as NAVTEX broadcasting employs 5 Bit Code as
ITA No.2 Code System (that is used for international telegraphic transactions by CCITT
Recommendations F.1), only 32 characters are available.
As it is impossible to display Text, Figures, Marks, Shift Signals only with 32 codes, the system
allocates the conversion signals and the figure conversion to Shift Signals and additionally allocates
26 codes.
The 32
nd
code is used to for the Korean shift code. 5Bit ITA code is converted to 7Bit and then
transmitted. All 7Bit codes are composed of 3(three) “ 1(B) ” and 4(four) “ 0(Y) ” and used for
checking any errors.
Besides, the system works on correcting any errors in the way of FEC(Forward Error Correction) that
the same characters are transmitted at the back of 4 characters(280mS) for comparison.
M
E
S
S
A
G
E
DX Signal
M
E
S
S
A
G
E
DX Signal
M
E
S M S E A S G
S E A
G
E
TX Character
M
E
S
S
A
G
E
TX Character
*Notes: Such cases may occur that the conversion code(Letter, Figure, Korean) is not received and
that the printing is faulty despite normal receipt of data.
1.3. Message Type
The message type of NAVTEX broadcasting is as follows. In transmitting, the system transmits
Message for matching with the receiver after transmitting Phase signal over 10 seconds. The general
message type is as below.
SNX-300
[518] [ 490] 10: 06. 02
ZCZC B1B2B3B4
Time of Origin(
)
Series ID + Consecutive No. (
………………………………….
Message Text(
)
…………………………………..
NNNN
PRT
NEXT
EXIT
In 0
Is 0
Ln 0
Ls 0
FEED
