rse is, thus, a first example of a variable-length code. Since the codeword length is decreased in proportion to the symbol frequency, we should expect that the entropy of Morse-code source is quite smaller than that of an ASCII code reduced to the same A-Z letters. In fact, the entropy analysis of the Morse code is not as straightforward as it may first appear. Earlier, I referred to the code as being pseudo-binary, even if it uses only two characters, which provided a hint. Indeed, the code makes use of short pauses or blanks between two codewords, without which the code would be unintelligible. For Information coding instance, the beginning message HELLO transmitted without blanks would look like which from Table 8.2 can be interpreted in several different ways (e.g., 5ELRJ or SVEFAM or EEEEEETIA2, etc.). This illustrates the property that, without such blanks, the Morse code is not uniquely decodable and is useless (say, except for mere SOS purposes). This notion of unique decodability will be further addressed in the next section. Here, we shall analyze what these information-less, but indispensable blanks represent in terms of code entropy.1 The idea to begin our analysis is to look at the blanks (/) as representing an extra symbol character in the Morse code, which is systematically present at the end of any codeword. Thus dit/ and da/ actually form digrams (two-character symbols) as opposed to monograms (single-character symbols). Two possibilities exist for introducing this extra blank symbol. The first possibility is to set the blank to a binary-code (dit/da) value, which must meet two requirements: (a) it is not already taken by any Morse code symbol, and (b) the concatenation of the blank to any Morse codeword, forming the new "digram" codeword, should be uniquely decodable. Referring to Table 8.2, the smallest binary symbol for "blank" should be With such a convention, whenever one hears six das, it is definitely a blank without ambiguity or error, and one knows for sure which other conventional Mors