General Information - SEA 7157 Operator's Manual

GENERAL OPERATIONS

GENERAL INFORMATION

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CAUTION
Do not attempt to transmit until the radiotelephone has warmed up for at least 30
seconds. Transmitting before the 30 second warm up period may cause a
violation of the Federal Communications Commission regulations.
PROPAGATION
Very High Frequencies (VHF) in the range of 30 MHz to 300 MHz may travel
far beyond the horizon under ideal conditions. For reliable communications,
VHF transmissions should be limited to no more than 30 miles.
INSTALLATION (RF grounding & DC connections)
The SEA 7157 may be configured to operate from either 12 or 24 volts DC
(direct current). Check the rear panel of the radio to determine the proper
operating voltage required. A direct connection to the power source is
recommended. Proper wire size must be used between the radio and power
source to prevent the DC voltage at the radio from dropping below 10.8 or 21.6
volts during transmit conditions. Should this occur, the radio may produce
distorted transmissions. Connect the RED positive (+) lead from the radio to the
positive supply terminal. The BLACK negative (-) power lead should connect to
the negative supply terminal. A #10 ground stud is provided for connecting the
radio chassis to the ship's earth connection with a copper strap.
The SEA 7157 is equipped with two UHF type RF connectors for the
installation of two independent antennas. One antenna allows constant
monitoring of the DSC channel while the other antenna labeled "ANTENNA 50
OHMS" is used for normal radio operations. The nominal impedance of each
antenna is 50Ω which requires high quality RG-213/U or equivalent coax.
It is recommended that an authorized SEA dealer perform the installation of your
VHF equipment to assure proper operation. For complete installation
instructions, refer to the "SEA 7157 Installation Manual" (OPR-7157-INST)
supplied with the radio.
RADIO PROTECTION
The chassis of the SEA 7157 is not connected to either supply rail. This allows a
direct connection to the ship's earth connection for voltage and RF interference
protection. In the event that the input voltage is reversed, the line fuse (7.5 amp
for 12 volt operation or 5 amp for 24 volt operation) will blow. It is also likely
that the internal reverse polarity protection diode CR20 will be damaged in order
to protect the remaining circuitry. Overvoltage to the radio will cause similar
results. If this should occur and a replacement fuse also blows, an authorized
SEA dealer should be contacted for proper service repairs.
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