Many makes of depth displays use a standard transducer such as those made by NASA, Airmar, B&G, Raymarine and other manufacturers worldwide. These work by transmitting and receiving a signal of around 150kHz, but some are lower frequency at 50-100kHz, and some are designed for deeper water at around 200kHz.
Having said that, you may find that ‘legacy’ (ie elderly) instruments are not too fussy about the frequency, so a sounder designed for 100kHz may work with a 150kHz transducer. As well as that the display heads and electronics
