Page 57 - HydrophoneHandbook_eReader_Ed2_20151208
P. 57

Frequently Asked Questions

Can I extend the cable length to my hydrophone without
affecting my measurements?
Yes, so long as the cable is connected after the preamplifier and
the detector input impedance matches the cable characteristic
impedance (should be 50 Ω).
If a cable is inserted between the hydrophone and preamplifier,
the cable contributes to the capacitance of the device and
consequently the sensitivity will change.
Additionally, there is a risk that the acoustic signal can excite
cable resonances.
Section 5.1.10 of IEC 62127-1 provides a guideline for picking an
appropriate length of cable:
To minimize the effect of resonance in the connecting cable, the
length of the hydrophone cable (in meters) shall be much less
than 50/(fawf + BW-20) where fawf is the acoustic working
frequency in MHz and BW-20 is the -20 dB bandwidth in MHz of
the hydrophone signal. In most cases a cable length of 15 cm
should be adequate.

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