DC-free error-correcting convolutional codes [comment and reply]

In a recent Letter, Deng et. al. (see ibid., vol.29, no.22, pp.1910-1911, 1993) reported a new class of convolutional codes which have both DC-free and error-correcting properties. The presented codes have a null at DC. However, there are some flaws in these codes. When encoding the information sequence with controlling the polarity of disparity d(t) of the codeword, the decoded sequence is different from the information sequence despite the error free condition. We show this by an example. A reply by Deng and Li is included