5 PTC-Firmware
37
K: Other NAV aid system Msg
L: Navigational Warning (2)
Table 5.5: NAVTEX message types
•
The next two places in the message identifier contain the message number. This
number belongs to a message of a particular type and remains unchanged when a
message is transmitted more than once. The numbers are consecutive. The number
has a decimal format and comprises 00 to 99. If an overflow occurs, i.e. "started"
again at 00, then usually, the "old" 00 message is no longer active, and permission
to erase has been granted, or has already automatically been erased by the
NAVTEX processor. This is naturally valid for all numbers in consecutive
operation. An exception can occur in the very numerous "Navigational Warning"
messages. That is why there are two different message type letters, A and L,
which actually describe the same type of message. This trick allows the possible
number of active "Navigational Warning" messages to reach 200.
5.8.3
Operating the NAVTEX Processor
The NAVTEX processor has only a single new command in the
cmd:-
menu. This is
NAVtex
. This command allows the complete configuration and activation of the
automatic NAVTEX processor. It operates in the background, as a completely seperate
process within the PTC-IIIusb multitasking environment.
When activated, the NAVTEX processor lays down a directory with the name NAVTEX
in the PTC-IIIusb mailbox, and stores all incoming NAVTEX messages there. The name
of the message author is given as "AUTO-NAV". The NAVTEX processor gives the
complete four figure message header as well as the plain language name of the type of
message. E.g. "CA03 Navigational Warning".
If the number of messages in the NAVTEX directory is exceeds the maximum allowed,
the NAVTEX processor deletes the oldest message it has previously stored before starting
to store a new message. (Messages from other sources which may also be in the
NAVTEX directory - such as operating instructions - are NOT deleted!). For details on
the
NAVtex
command refer to chapter
.
5.8.4
Notes about NAVTEX practice
The PTC-IIIusb normally operates with 200 Hz shift for FSK operation. Although
NAVTEX uses 170 Hz shift, it is not necessary to change the modem tone settings for
NAVTEX reception. The loss due to the slightly maladjusted shift being in the area of
tenths of a dB, and can be ignored for practical purposes.
When using the usual modem tones of 1400 Hz and 1200 Hz (Low-tones,
TOnes
parameter 0), the receiver should be set to USB and a frequency of 516.700 kHz to
receive NAVTEX on a center frequency of 518 kHz. For LSB the frequency should be set
to 519.300 kHz. Here, the
TR
parameter should be set to 1 or 3 (refer to chapter
).
Basically, the same conditions for NAVTEX reception are required as for AMTOR-FEC.
The parameters
BC
and
ARX
must both be set to 1. (these are the default values. Refer to
).