L3 comminications SERIES 5000, Руководство по эксплуатации и обслуживанию

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Theory of Operation
1-7
to allow the receive signals to enter a fixed gain low noise preamplifier stage.
The output of the preamplifier is input to a voltage controlled amplifier (VCA)
which performs the TVG function. The gain versus time relationship, TVG,
that is applied identically to all channels is digitally synthesized from a
predefined curve stored in a PROM on the Multiplexer board. Provision has
been made for the storage of alternate TVG curves but in practice it has been
found that the use of these has been limited to test procedures.
Each of the receiver channels is bandpass filtered with tightly matched filters
providing a -3dB bandwidth of 20 kHz, centered at 455 kHz. The filtered
signal is then output to the Multiplexer board for subsequent sampling.
Sensor Interface board.
The Sensor Interface board conditions sensor data
from the compass board, depth pressure sensor, altimeter, and optional devices
for subsequent multiplexing and transmission to the TPU.
Multiplexer board.
The Multiplexer board digitizes the signals from each of
the transducer sub-array channels along with the signals from the sensors,
encodes the data, and transmits a high baud rate digital data stream to the TPU
via the tow cable. The Multiplexer board also receives the trigger signal and
command messages which instruct the Transmitter board to fire the arrays and
configure aspects of towfish operation. The Multiplexer board also acts as a
motherboard for the other boards providing the connections and distributing
power.
The Multiplexer board uses a proprietary sampling scheme that preserves the
phase of the individual channel signals, but only requires a single A/D
converter, thereby reducing cost and power consumption while eliminating the
phase mismatch between converters of alternate dual converter schemes. The
output of the A/D is input to the data encoder and converted to serial data for
subsequent transmission up the tow cable.
A full duplex hybrid allows data transmission up the cable while
simultaneously receiving the FSK trigger signals and power. The downlink
signals are input to FSK demodulators, and the baseband outputs are routed to
the Transmitter board, indicating when to fire the main array, and to a micro
controller that handles towfish configuration.
Towfish connector.
The towfish connector pinouts are shown in Table 1-1,
and the connector is shown in Figure 1-4. Only two pins are used.
Table 1-1:
Towfish Connector—at Towfish
PIN NO. LABEL FUNCTION
1
Power/Data +200 VDC power and multiplexed data
2 Shield Power and data return