5 PTC-Firmware
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also not exactly customized to enhance the sleep of the crew. The power
requirements at night should thus be kept as low as possible. A continuously
running laptop or other computer is a relatively large load for the energy supply of
a small ship. A NAVTEX controller should therefore be able to operate without
any additional computer, and use little electrical energy itself.
The NAVTEX processor of the PTC-IIIusb solves many of the disadvantages mentioned
above. It enables:
•
Automatic, selective reading of NAVTEX transmissions. Either the code for the
type of message or the regional code can be selected.
•
Automatic processing of transmissions received more than once. Only the best
copy is held. Old data is automatically deleted.
•
A fast check on the type of received messages.
•
A memory buffer is available without using an external computer, as the
NAVTEX processor uses the PTC-IIIusb internal mailbox as a message store. It
automatically lays down, if not already there, a subdirectory called NAVTEX in
the PTC-box. Data written into the mailbox by the NAVTEX processor can be
accessed via PACTOR or Packet-Radio.
5.8.2
The NAVTEX System in Detail
As mentioned above, NAVTEX messages are sent in plain language using SITOR-B
coding. To mark the beginning, end, and type of message, NAVTEX uses a simple
convention:
•
Every message begins with the characters ZCZC, followed by a space. Then
follows the four figure message identifier plus a carriage return. The actual
message now follows.
•
Every message finishes with NNNN. (If these end characters are mutilated, the
NAVTEX-processor finishes writing the message at the latest after loss of receive
synchronization).
The message identifier is constructed as follows:
•
The first character is a letter, with a range of A to Z. This letter sets the area code
and is allocated to one transmitter in the reception area. Which letter is allocated
to which transmitting station can be seen relatively fast, as the transmitting station
is usually also mentioned in the message itself.
•
The second letter describes the type of message. The following types are presently
defined:
A: Navigational Warning
B: Meteorological Warning
C: Ice Report
D:
Search and Rescue Info
F: Pilot Message
G: DECCA
Message
H: LORAN-C Message
I:
OMEGA Message
J:
SATNAV Message
