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Hydrophone Handbook

                        Calibration

8.6 Considerations Regarding Electrical Loading Conditions

Because a hydrophone's sensitivity depends on the electrical
impedance of the detector or amplifier to which it is attached
to, modular hydrophones are sold with an open-circuit
calibration, called formally the "End-of-cable Open Circuit
Sensitivity", or EOC sensitivity for short, and designated as
Mc(f). Mc(f) is determined by measuring the sensitivity of the
hydrophone with a laboratory amplifier, and then subtracting
the effect of that amplifier's gain, as well as that of its finite
(i.e., non-infinite load).

Note that the HGL, HNP, and HNC hydrophones may be
connected directly to an amplifier without any cable, so the
EOC sensitivity is defined as the sensitivity that would be
measured at the hydrophone's connector into an infinite load.

If the hydrophone and amplifier impedances are primarily
capacitive, the loaded sensitivity,    , can be estimated as
follows:
                                                     
        ()     =        ()    +    +  

Where:

G(f) = amplifier gain (as a function of frequency)

    MC(f) = hydrophone EOC sensitivity
    CH = capacitance of hydrophone
    CA = capacitance of amplifier
    CH = capacitance of connector
Customers are advised to perform their own assessment of the
accuracy of the above equation fore their configuration. In
particular, customers should be aware that extension cables
connecting the hydrophone to the preamplifier or detector

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