The compact and flexible Apsu instrument has been developed to deliver 105 A and up to 150 kW of instantaneous power during the transmission. The Apsu transmitter unit (ApsuTx) control and regulate this high current where some amount of transmission power is dissipated as thermal energy. Therefore, thermal management of this unused power becomes an impotent concern for reliable operation of the ApsuTx, especially for new steady-state sequences. We briefly introduce the ApsuTx circuit and provide a mathematical formulation for electrical power dissipation. This formulation is used to design the thermal model of ApsuTx and it is evaluated using different input sequences. The comparison results showed that 33.93 W is dissipated by steady-state sequences, which is approximately ten times more than with conventional pulses. This power can only be dissipated safely by a heatsink with a maximum thermal resistance of 1.832 oC/W. A small size heat sink (300 mm × 200 mm × 8 mm) has been designed and installed with a lower thermal resistance than the calculated value. This provides a compact and lightweight solution for remote
field measurements.