End of emission

The Transmitter Identification Character (B₁)

The Transmitter Identification Character (B₁)is a single unique letter that is allocated to each transmitter. It is used to identify the broadcasts, which are to be accepted by the receiver, and those, which are to be rejected.

In order to avoid erroneous reception of transmissions from two stations having the same B₁ character, it is necessary to ensure that such stations have a large geographical separation. This is achieved by allocating B₁ characters by alphabetical sequence through each NAVAREA of the World-Wide Navigational Warning Service.

NAVTEX transmissions have a designed range of about 400 nautical miles. The minimum distance between two transmitters with the same B₁ identifier is usually sufficient to ensure that a receiver cannot be within range of both at the same time.

Subject Indicator Character (B₂)

Information is grouped by subject on the NAVTEX broadcast, and each subject group is allocated a subject indicator character B₂. The subject indicator character is used by the receiver to identify different classes of messages as listed below. The indicator is also used to reject messages concerning certain optional subjects which are not required by the ship. For example, OMEGA messages might be rejected in a ship which is not fitted with an OMEGA receiver. Receivers also use the B₂ character to identify messages which, because of their importance, may not be rejected. The following subject indicator characters are in use:

A – Navigational Warnings (cannot be rejected by the receiver)

B - Meteorological Warnings (cannot be rejected by the receiver)

C- Ice Reports

D – Search and Rescue Information (cannot be rejected by the receiver)

E – Meteorological Forecasts

F – Pilot Service Messages

G – DECCA Messages

H – LORAN Messages

I – OMEGA Messages

J – SATNAV Messages

K - Other Electronic Navaid Messages (messages concerning radio navigation services)

L - Navigational Warnings-additional to letter A (should not be rejected by the receiver

(continuation of B₂ subject group “A”))

V – Special services – trial allocation

W – Special services – trial allocation

X – Special services – trial allocation

Y – Special services – trial allocation

Z – No messages on hand

Message Numbering (B₃, B₄)

Each message within a subject group is allocated a serial number B₃, B₄ between 01 and 99. This number will not necessarily relate to series numbering in other radio navigational warning systems. On reaching 99 numbering will re-commence at 01 but avoiding the use the message numbers still in force.

A shortage of numbers will, where possible, be alleviated by allocation of messages to other, relevant subject groups, and B₂ =L may be used for additional navigational warnings, to receive the overflow from B₂ =A when necessary.

2. Answer the following questions

1. What is the NAVTEX?

2. What are the principal features of NAVTEX?

3. What priorities exit for NAVTEX messages?

4. What is the standard format of NAVTEX messages?

5. How is the transmitter identified?

6. In what way is the subject indicated?

7. How are the messages numbered?

3. Translate the following NAVTEX message bearing in mind various indicators

LA 61

201355 UTC OCT 04

LIMNOS RADIO NAVWARN 193/04

TUG BOAT ALEXANDROS / SV5120

WITH TOWING LINE LENGTH 300 METRES

IN PSN 40 24 N – 022 47E ON 201430UTC

FROM THESSALONIKI PORT TO PIRAGDIKIA

POINT OF CHALKIDIKI PENINSULA

ETA 211105 UTC

COURSE VARIOUS SPEED ABT 5.5 KNOTS

WIDE BERTH REQUESTED

NNNN

UNIT 6