Sailor RM2042, Техническое руководство, Страница: 14 / 106

1 INTRODUCTION RM2042
1.4 PRINCIPLE OF OPERATION AND BLOCK DIAGRAM
RECEIVER
The RF-signal from the antenna is feed to the input amplifier circuit. Here is the initial filtering made by
means of a fixed, double tuned filter before the signal is amplified in the front-end amplifier. This amplifier
is followed by another fixed, double tuned filter. The amplified and filtered signal is feed to the first mixer
stage.
This stage converts the received signal to the first IF frequency on 15.3 MHz. The local oscillator for
this stage is created by means of an XTAL oscillator running at 141.225MHz.
The signal is filtered by means of an XTAL-filter, amplified and then feed to the integrated IF-circuit. This
circuit includes the second XTAL-oscilllator circuit running at 14.85MHz, the second mixer stage and
following limiting amplifiers and detector circuits.
The filtering on the second IF-frequency at 450kHz, is made by means of a ceramic filter.
The detected AF-signal is led through an electrical controlled switch, which is only used for loop back
test purpose. The output from this switch is filtered in the deemphasis filter, before the AF signal selection,
where the selection between the build-in channel-70 receiver and the connected VHF radiotelephone is
performed.
The switch setting of the AF selection is determined by the actual operation of the unit and signal strength
on Channel-70, giving full priority to the Channel-70 receiver output.
From the connected VHF-radiotelephone, the detected AF-signal is feed to a deemphasis filter and a
carrier detect circuit, which provides the needed signals for the demodulator when you are using the public
call facilities.
The selected AF-signal is furthermore feed to the interface board, where it is amplified to source an
internal loudspeaker.
The FSK-modem performs the demodulation of the received FSK-signal, and the modulation of the AF-
signal for the transmitter. The circuit is controlled from the microprocessor board.
Internal power supply for the board, is generated with two regulators, one for 5V and one for 10V.
A power low condition is signaled from the 10V regulator to the microprocessor unit, to secure a controlled
power down sequence.
INTERFACE
This module provides the necessary connections between the modules and between the modules and
the externally connected equipment, such as power supply, VHF-transceiver, telephone handset, printer
etc.
This unit must be supplied with 12V DC, which can be provided either directly from batteries or from N420,
24 to 12V converter. The proper operation of the ON/OFF switch is selected by means of the 12/24V wiring
circuit.
Fuse and over/reverse-voltage protection is placed on this module as well.
The 5V power supply for internal digital boards are made on this unit.
The AF power amplifier for the loudspeaker is supplyed by its own 5V regulator and the AF comes from
the receiver module. Alarm and mute signals are generated on the microprocessor module and feed to
the amplifier chain.
Distress channel information for a connected scrambler, is buffered and level shifted, before it is feed
to the 9-pole connector.
AF output for the connected transmitter is buffered and level adjusted in different amplifiers.
When the unit is operating in an automatic system with a VHF-transceiver, is the AF output delivered
as an unbalanced signal adjusted in level to fit the microphone input sensitivity of the transceiver.
When the unit is operating as a DSC-encoder is the AF output port swiched to supply the signal on a 600
ohm balanced output port. The level can be adjusted to 0dBM 10dB by means of a trimming
potentiometer.
When the VHF port communication switch is set for an automatic system, the serial communication link
to the transceiver will be connected to the 9 pole output connector for the VHF.
The remaining circuits on this module consists of input buffers and level shifters for the i/o links to the
microprossor. These links are used for the NMEA interface, printer interface and the interface to C2149,
remote distress unit, or a PC for programming or remote control.
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