Setup – Blockage & RF Radiation Hazard Zones
ST94-21 C/Ku-Band TVRO
10-2
When used for “
FCC TX Mute
” logic output for a single Sea Tel TXRX antenna, this output is used to suppress RF
transmissions whenever the antenna is mis-pointed 0.5 degrees or more, is blocked, searching, targeting or
unwrapping. The SW2 output would be interfaced to the satellite modem to disable/mute the TX output signal from
the Satellite TXRX Modem. When the mute condition is due to antenna mis-pointing, it will not un-mute until the
pointing error of the antenna is within 0.2 degrees. The default output is contact closure to ground when the antenna
is mis-pointed, therefore providing a
ground
to “Mute” the satellite modem from the SW2 terminal of the Terminal
Mounting Strip. If your satellite modem requires an
open
to “Mute”, refer to SYSTEM TYPE parameter 16 value to
reverse the output logic from the ACU.
Programming instructions:
Determine the Relative AZ positions
where
blockage, or RF Radiation Hazard, exists. This may be done by monitoring
the received signal level and the REL display readings while the ship turns or by graphing the expected blockage
pattern. Elevation of the antenna in normal use also must be taken into consideration. A Mast or other structure may
cause blockage at low elevation angles, but may not cause blockage when the antenna is at higher elevation angles
where it is able to look over the structure. Up to four zones may be mapped. Only zones which are needed should be
mapped (in AZ LIMIT pairs).
In unlimited antenna systems the Relative position of the antenna must have been calibrated by properly setting the
Home Flag Offset (HFO) value in the PCU. The HFO calibrates Relative to display 0000 when the antenna is pointed in-
line with the bow of the boat/ship (parallel to the bow).
Convert the relative readings to AZ LIMIT/EL LIMIT values by multiplying by 10. Enter the beginning of the first
blockage region as AZ LIMIT 1 and the end of the region (clockwise direction from AZ LIMIT 1) as AZ LIMIT 2
parameters in the ACU. If needed, repeat setting AZ LIMIT 3 & 4 for a second ZONE and then AZ LIMIT 5 & 6 if a
third ZONE is needed. All unneeded zone AZ LIMIT pairs must be set to 0000. Set the upper elevation limit of each
blockage zone (also entered in degrees multiplied by 10).
EXAMPLE 1 - Three blockage Zones: A ship has a Sea
Tel antenna mounted on the port side and an Inmarsat
antenna mounted on the starboard side. A mast forward, the
Inmarsat antenna to starboard and an engine exhaust stack
aft form the three zones where satellite signal is blocked (as
shown in the graphic). In this example zone 1 is caused by
the mast, zone 2 is from the Inmarsat antenna, zone 3 is
from the stack and zone 4 is not needed:
ZONE 1 begins (AZ LIMIT 1) at 12 degrees Relative
and ends (AZ LIMIT 2) at 18 degrees Relative.
Multiply these Relative positions by 10. Enter AZ
LIMIT 1 value of 0120 and AZ LIMIT 2 value of
0180. In this case the mast height only causes
blockage up to an elevation of 50 degrees, so we
set EL LIMIT 12 to 0500. If the antenna is between
these two AZ Limit points but the elevation is
greater than 50 degrees, the antenna will no longer
be blocked.
ZONE 2 begins (AZ LIMIT 3) at 82 degrees Relative
and ends (AZ LIMIT 4) at 106 degrees Relative.
Multiply these Relative positions by 10. Enter AZ
LIMIT 3 value of 0820 and AZ LIMIT 4 value of 1060. In this case the Inmarsat antenna height only causes
blockage up to an elevation of 12 degrees, so we set EL LIMIT 34 to 0120. If the antenna is between these
two AZ Limit points but the elevation is greater than 12 degrees, the antenna will no longer be blocked.
ZONE 3 begins (AZ LIMIT 5) at 156 degrees Relative and ends (AZ LIMIT 6) at 172 degrees Relative. Multiply
these Relative positions by 10. Enter AZ LIMIT 5 value of 1560 and AZ LIMIT 6 value of 1720. In this case
the stack antenna height only causes blockage up to an elevation of 36 degrees, so we set EL LIMIT 56 to
0360. If the antenna is between these two AZ Limit points but the elevation is greater than 36 degrees, the
antenna will no longer be blocked.
ZONE 4 is not needed. Enter AZ LIMIT 7 value of 0000 and AZ LIMIT 8 value of 0000. Set EL LIMIT 78 to
0000. If your ACU software includes 5 volt polarization you will not see these AZ & EL LIMIT parameters.
EAR Controlled - ECCN EAR99
Summary of Contents for ST94-21
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