Service manual

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SMARTFIND NAVTEX service manual Page 22
4. ON-SHIP ASSESSMENT
Also refer to APPENDIX 3: SEA TRIAL CHECK LIST
General information regarding optimising NAVTEX Reception
When sailing within a published NAVTEX service area, reception coverage can
extend as far as 200 - 300 nautical miles. If the NAVTEX signal has to cross land to
any significant extent, attenuation may occur and this can reduce the reception range
to as little as 50 miles. Range can increase significantly at night; it can sometimes
extend to as much as 1000 miles. Some NAVTEX stations reduce transmitter power
at night to avoid overlap of signals into other sea areas.
Background electrical noise in harbor, the presence of high cliffs and the masts of
surrounding vessels can all contribute to poorer NAVTEX reception when in harbor
rather than at sea.
To ensure the best reception possible the NAVTEX antenna must be located in a
zone that is free of other electrical equipment. Take care to avoid locations that are
close to wind generators, battery chargers, shore power transformers and any
associated electrical power wiring. If there is any doubt regarding the suitability of a
proposed location, first make a temporary test installation to confirm that the
reception performance meets requirements before committing time and effort to a full
antenna installation that may later have to be changed.
System Grounding
It is mandatory to have a grounding connection made to the earth terminal on the
rear side of the case. This will lower the signal to noise ratio and increase the
sensitivity of the system and hence the range of reception, Ensure that the 1/8”
spade terminal ground pin at the SMARTFIND NAVTEX is connected to a good
electrical ground. This should be the ship’s hull or a specially installed ground plate,
or the keel bolts on a non-encapsulated keel or bonded hull skin fitting. Use a
minimum cable size of at least 1.5 mm
2
. Check the installation guidelines for the
antenna type being used to ensure its correct grounding requirements are complied
with. Note that connection to an inappropriate or electrically noisy ground point can
sometimes give unpredictable results and may even reduce overall reception
performance. Consequently, do not make a new ground connection and assume that
it will make things better; always check that reception is better before committing to
that connection.
Isolating sources of on board interference
The ‘Setup mode Receiver options’ monitor window can be used to display NAVTEX
reception in real time. Use it to prove that the system is receiving correctly.
The information shown on the monitor page is totally independent of normal
operation, station and message type selection filters. As soon as live NAVTEX
reception is detected, received information will start to flow across the display in real
time. Non-printing, transmitter-idle and phasing characters are displayed as well as
actual message text.
Select the required NAVTEX channel using the Monitor Source’ menu option.