Interface (Module 1) Part No. 626941 - Sailor RM2042 Technical Manual

5 CIRCUIT DESCRIPTION AND SCHEMATIC DIAGRAMS

5.1 INTERFACE (MODULE 1) PART NO. 626941

All connections to external equipment and the corresponding interface circuits are located at the interface
module. The interface circuits are in this discription divided into the following blocks, which again are
divided into an analog and a digital groupe:
Analog interface
Loudspeaker amplifier
Balanced TX AF amplifier
Unbalanced TX AF amplifier
12V/24V wiring circuit
5V power supply
Power failure reset circuit
Digital interface
S.P. bus interface
Printer interface
C2149/PC interface
NMEA interface (Navigational equipment interface according to the National Marine Electronics
Association)
LOUDSPEAKER AMPLIFIER
The loudspeaker amplifier is build-up around the integrated power amplifier TDA7052 (U4), which has
a voltage gain of about 40dB and is able to deliver about 0.5 Watt into an 8 ohm loudspeaker.
In a normal operation situation, where no call signal has been detected, the received signal from the
external connected VHF or the build-in channel-70 receiver will be leaded to the internal loudspeaker. The
received signal comming from the receiver module is buffered by an operational amplifier (U3.4) and is
then led to the volume control at the front panel, where it is attenuated. The attenuated signal is buffered
at the interface module by the transistor Q8 and then finaly led to the power amplifier and loudspeaker.
If a call signal (distress or ordinary) is received, the microprocessor will generate an indication signal
(gated 600Hz tone) that will be leaded to the loudspeaker instead of the received signal. The received
signal is removed from the loudspeaker by means of the transistor Q3, which at the same time is
grounding the signal and removing the bias for the buffer transistor Q8. The controle signal to transistor
Q3 is generated by the printer interface unit U10 and is filtered by R13, R14 and C52 to avoid a suddenly
change in the bias of transistor Q8, which else would result in an irritating "DC-blop" in the loudspeaker.
BALANCED TX AF AMPLIFIER
The VHF DSC RM2042 has two seperate transmitter outputs - an unbalanced with a low generator
impedance and a balanced with a 600 ohm generator impedance. To establish a balanced connection
between RM2042 and the connected VHF radiotelephone, it will be necessary to use two wires, while an
unbalanced connection only requires one. Because the number of wires in the connection cable is limit
to nine and all are in use, it is necessary to change the function of the serial data bus and use this as the
second wire in the balanced connection. As a consequence, the balanced connection can not be used
in instalations where RM2042 is connected to the duplex VHF radiotelephone RT2047 or the simplex VHF
radiotelephone RT2048, because the serial data communication is essential in these cases. The
switching between balanced and unbalanced mode is done manualy by turning the switch S1 with a
screwdriver or equal.
The input signal to the balanced TX AF amplifier is a FSK-signal (Frequency-Shift Keying signal), which
is generated by the MODEM-IC located at the Receiver Module. This FSK-signal is led to the operational
amplifier (U3.2) and the transistor Q4 at the Interface Module. The feedback signal to the OP AMP is taken
from the emitter of Q4, which minimize the harmonic distortion. The balance is obtained by means of the
transformer TR1, which is placed between the battery voltage and the collector of Q4. The output level
is adjustable from -10dBm to +10dBm (600 ohm) and is controlled by the trimming potentiometer R17.
9716
RM2042
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