Ian Waugh - A Mariner\'s Guide to Marine Communications

1 Antenna(s): receivers that operate on SIHkHz (only) will have a single

antenna, which may be passive or active. A passive antenna does not

increase the level of, or boost received signals. An active antenna

uses an amplifier to boost received signals. Receivers that operate on

518kHz and one of the other, additional, frequencies (490kHz or

4209·5kHz) may have two passive antennas, one tuned to each

frequency, or a single broad band antenna, connected to serve both

receiver paths.

2 Co-axial cable: the cable

connecting the antenna(s) to the weatherproof

copper shield to block

electrical interference

receiver will be co-axial-having

a central copper core for the

received signal path and an outer

screen to shield the central core

protecting the core from

external signals and electrical

noise.

insulation

central copper wire

(receiving path)

Figure 9.3

Co·axial cable

3 NA VTEX receiver: at the time of writing, most receivers only operate
on 518kHz, though some can be upgraded with a second frequency,
if required. Some also have a facility for connecting an external
receiver to provide reception on an additional frequency. All receivers
have a paper printer (4) and a programming area (5). Receivers with
518kHz and an additional frequency will become more common now
that the additional frequencies are coming more into use around the
world.

4 Paper printer: all GMDSS-approved NAVTEX receivers must print

received messages onto paper. A VDU is not sufficient. Printer paper

is usually thermal and will only print on one side. When loading

paper, you need to make sure that:

• The paper is the correct way up.
  The paper is loaded squarely into the printer.
  5 Programming area: the programming area will have a selection of
  buttons, controls and/or displays, which may include:
  Power on/off switch.
  Visual Display Unit (for displaying receiver status - what station{s)/
  messages are programmed; last message received, etc.).
  Illumination/dimmer (for the VDU).
  Programme status key (for printing/displaying the current station/
  messages programmed status).


• Station/message programming keys {may be dual-function with

MARINE COMMUNICATIONS 183