This circuit allows the entrance of the fan to 50% of its speed thus slowing the time Yaesu FT-840 triggers the circuit to its thermal entry at top speed. This effect reduces the noise This circuit allows the entrance of the fan to 50% of its speed thus slowing the time Yaesu FT-840 triggers the circuit to its thermal entry at top speed. This effect reduces the noise of the device since its performance at high speed is not to be so ordered.