The commenter points out that the recursive algorithm described by K. Metzger in the above-titled letter (ibid., vol.76, no.5, p.634-5, May 1988) was published by him in the September 1980 issue of the IEEE Circuits and Systems Magaz (vol.2, no.3, p.3-5). He notes that the recursive technique is very useful not only for the low-pass to bandpass transformation, but also for performing the bilinear transformation used in digital filter design. The author replies that he was unaware of the earlier paper and thanks the commenter for calling it to his attention.>

A maximum a posteriori (MAP) symbol synchronizer is implemented using commercially available charge-coupled devices (CCD's). The use of the CCD permits a direct realization of the closed loop form of the MAP synchronizer and has the added advantage of adaptive tuning of the matched filter with symbol rate.

A tunable matched filter for the major PCM codes has been synthesized utilizing a developmental bucket-brigade delay (BBD) line. The variable delay feature of the BBD allows continuous tuning of the matched filter over a wide range of bit rates. By combining and weighting the outputs of two BBD lines, matched filters for nonreturn-to-zero (NRZ), return-to-zero (RZ), and biphase codes are realized with a signal-to-noise performance within 0.8 dB of theoretical.