[![I've attached schematic, I am connecting transducer directly to that header pins on receiver side. On transmitter side I am connecting op-Amp to boost voltage to +10v -10v.]]I am working on Acoustic underwater communication system at 60 kHz. I am using Op-Amp on transmitter side which amplifies signal to -10v to +10v. I observed a weird thing about this system that it only works when it is grounded to my home's common ground. For example if I supply power through separate battery it wont work. But if I supply it through adapter on both transmitter and receiver side it works fine with reasonable range. Anyone has any idea why it behaves like this and how to fix it? I really appreciate your help.
The most likely answer without measurements or schematics is that you transponders are connected to earth by the coupling Capacitance of water , while the common mode of a floating battery to an unbalanced electronic circuit has more antenna effects pickup up one side of the battery terminal circuit (0V gnd plane) than the other from high E-field line signals.
Thus shunting the battery to PE earth reduces these ambient line CM signals. Also using a cap should work as well.
An alternative solution could be to use a CM choke or 1:1 audio transformer with good accurate 1:1 ratios to act as BALUN or CM choke to convert UNbalanced circuit into a BALanced circuit.
Although the circuit is not posted yet , an audio transformer just isolates this from ground making unbalanced inputs sensitive to common mode line noise interference. A CAP or earth ground is necessary to shunt the CM interference or a BALUN transformer in series to balance the interface and attenuate the common mode noise.