The BER of a 16QAM signal in an AM/16QAM hybrid optical transmission system is tested. A floor is observed in the measured BER. Such a BER floor is due to ‘impulsive distortion’ caused by clipping. The BER is calculated based on the Middleton class A model, under the supposition that a statistical-physical model of ‘impulsive distortion’ is similar to that of impulse noise. The calculated and experimental results are in good agreement.