A novel partially coherent detector for joint data detection and carrier phase estimation of continuous-phase-modulated (CPM) signal is presented. The algorithm differs from coherent Viterbi algorithm only in the metric which it maximizes over the possible transmitted data sequences. This metric is influenced both by the correlation of the hypothesized signal with the received one and the current carrier phase estimate. The system has been simulated and comparisons made with existing detection techniques on channels with additive white Gaussian noise and carrier phase jitter. Simulations of the detector are used to assess the relative susceptibility of different CPM (continuous phase modulation) schemes to phase jitter. The trend is that narrower band schemes are more sensitive to carrier phase inaccuracy than the less spectrally efficient ones. >