[Cin] OT: when you try to record dolphin, but result is mostly radio interference

[Mat]

The radio signals which are interfering could be shortwave. 

I would recommend using ferrite clamps on the cables which do not carry
digital signals, especially those in the most sensitive area, like
from the hydrophone and pre-amp. Also the pre-amp power cable, if it is
not battery powered. And screen the pre-amp, if it is not in a metal
box. The pre-amp itself ought to have provisions for preventing this,
like a low-pass filter at the input.

MatN