The secondary positioning encoder is used to test the transponder, including encoding, power reading and testing. The encoding function is used to write the address into the transponder, because each transponder needs an independent address before it goes into the water, otherwise it can't be positioned properly. The transponder is powered by 12-volt dry cell batteries, and the voltage of this battery pack is more than or equal to 12V when it is fully charged, and it needs to replace the batteries when the voltage of the batteries is less than 9V. When the battery voltage is less than 9V, the battery needs to be replaced. The battery reading function of the encoder is used to read the battery voltage inside the transponder, to prevent the transponder from not working properly after being launched into the water due to insufficient voltage, and the test function of the encoder is used to check whether the function of the transponder is normal or not, and to ensure that the transponder can carry out normal ranging after being launched into the water when it tests normal.