903-0628-00 Rev. 1
Model 903-HD User's Guide – FMB-X-2.5
Focal Technologies Corp.
Page 4-23
Although the card is configured to operate with two-wire, un-amplified hydrophone inputs, the hydrophone
plugin may be factory modified to p12V to an external hydrophone pre-amplifier on a third conductor
and bypass the gain of the internal pre-amplifier.
Pin designations for the AIB-HYDRO plug-in modules are given in the table below.
Table 4-12: AIB-HYDRO Pin Designations
Pin
Designation
1
Chassis* (optional)
2
N/C (+12 VDC optional)
3
- Signal (GND on output)
4
+ Signal
*The chassis pin is normally left open on the mating connector.
Frequencies from 16 Hz to 28 kHz (-3 dB points) are passed through the system, though frequencies slightly
outside this range may be transmitted if the added loss can be compensated by additional S1 gain. If low
frequency noise pick up (typically 50 or 60 Hz) is introduced by improper shielding, the lower cutoff frequency
may be raised by adding a shunt resistor across pins 3 and 4 to attenuate the lower frequencies. The chassis
pin on the WAGO connector should be connected to the shield of the hydrophone cable.
The analog signal on the input board (remote end) is digitized at 73 kilosamples per second with a 12-bit
resolution after amplification and reconstructed at the output board (console end) with no additional gain.
(Switch bank S1 is not active when the hydrophone board is configured for output.) Output impedance is
approximately 34 ohms, which is suitable for high impedance loads and is even capable of directly driving
8-ohm speakers, although with a corresponding loss in output power. Maximum output level is limited to
2 Vpp, yielding a dynamic range of roughly 66 dB.
AIB-HYDRO cards may be modified for compatibility with different input voltage levels, such as IRIG-B or
outputs from pre-amps. For large input signals (> 45 mVpp) the on-board pre-amp is typically bypassed.
Modified AIB-HYDRO cards will have different variants in the part numbers (-XX). For example, AIB-HYDRO
with P/N 903-0244-02 is modified to p12 VDC supply at the Wago connector on pin 2, and the input
pre-amp is bypassed. (The 903-0244-02 is only used at the subsea for connection to the hydrophone; the
standard 903-0244-00 should be used at the surface.)
Summary of Contents for Focal 903
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