[![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.][1]][1]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.

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    $\begingroup$ Posting a schematic would help us understand your problem. $\endgroup$
    – Gil
    Aug 2 at 23:29
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    $\begingroup$ One possibility: because the whole thing doesn't work as designed (at least in the environment you're testing it in) but it can sneak a signal through the power wiring. $\endgroup$ Aug 3 at 0:31
  • $\begingroup$ Hi I've attached schematics, let me know if you have any solution in mind. Thanks a lot $\endgroup$ Aug 5 at 21:41
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    $\begingroup$ The schematic image is missing. It looks like you may have added an image, but deleted the actual URL from the text so it doesn't exist. Please try again. $\endgroup$
    – Kevin Reid AG6YO
    Aug 5 at 21:51

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.

Rev A

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.

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    $\begingroup$ Hello Tony! Although IMHO the OQ is OT, we look forward to seeing more answers from you here. :-) $\endgroup$
    – Mike Waters
    Aug 4 at 22:25
  • $\begingroup$ Thanks for your response, I am using audio transformer, I've just put schematics in my question. I'm considering to add bandpass filter on receiver side. Probably it might fix the issue. I'm not sure though. $\endgroup$ Aug 5 at 21:40

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