Are they looking for a 37 kHz radio signal or audio signal? Big difference. And yes u can still buy crt Cro,s. And LCD oscilloscopes, so are they listening for sound waves in which case u use a transducer or radio waves which travel under water?? To subs at 65 kHz,
As mentioned earlier, a 37kHz radio signal is in the LF range and needs a very large antennae and considerable power to radiate any significant range.
37kHz audio, is in the VHF audio range capable of being detected with a transducer and then displayed on the appropriate equipment.