The effects of partial-band-noise jamming and additive white Gaussian noise on the bit-error rate (BER) performance of fast frequency-hopped M-ary frequency-shift-keying (FFH/MFSK) systems over frequency-selective Rician-fading channels are studied. The FFH/MFSK systems employing the linear-combining receiver and the product-combining receiver are investigated. The analytical BER expressions are derived based on characteristic function approach, which is applicable for higher diversity levels. The analytical expressions, validated by simulation results, show that the product-combining receiver is superior to the linear-combining receiver when the jamming power is relatively strong.