NAVTEX / AMTEX
48
NAVTEX / AMTEX Mode
KAM
only
NAVTEX / AMTEX Theory
NAVTEX transmissions are, in reality, Mode B AMTOR (FEC). What makes NAVTEX unique how-
ever, is the actual message format. NAVTEX stations always transmit on 518 kHz LSB and are typi-
cally located on the coast lines. The same format is now being used by the American Radio Relay
League (ARRL) to transmit their bulletins on a daily basis. These are transmitted during their
scheduled teleprinter bulletins.
At the beginning of a NAVTEX (or AMTEX) transmission, the sending station will send a preamble,
identifying the station that is transmitting, the type of message and the message sequence num-
ber. The preamble would look like this:
ZCZC AG25
The ZCZC is always present and the receiving unit sees this as the identification that the identifier
is coming next. The components of the identifier, as defined in the NAVTEX documentation are:
B1 B2 B3 B4
B1 is used to identify the station that is transmitting and consists of the letters A through Z. B2 in-
dicates the message class (A through Z). Note that class A, B and D messages must always be
printed once. B3 and B4 are the sequence number for the message and will have values from 00
through 99. Messages with sequence number 00 are always printed. When the message number
reach 99, they wrap to 01 as the next number.
Currently operating NAVTEX stations are:
Halifax, Nova Scotia
Guam
Boston, MA
Honolulu, HI
New Orleans, LA
Kodiak, AK
Miami, FL
Astoria, OR
San Juan, P.R.
Long Beach, CA
Chesapeake, VA
San Francisco, CA
For NAVTEX messages, the currently assigned message classes are:
A
Navigational warnings
B
Meteorological warnings (storm warnings)
C
Ice reports
D
Search and Rescue Information
E
Meteorological forecasts
F
Pilot message
G
Decca message (Decca is offline since March 2000)
H
LORAN-C message (LORAN-C is offline since September 2010)
I
Omega message (Omega is offline since September 1997)
J
differential Omega message
Z
QRU – no message on hand
K–Y
Reserved
NOTE: K has been proposed for "other electronic navigational aid system message".
