Morse code in Cayo Largo del Sur, Cuba is coded as "UCL", and UCL in Morse code is transmitted on its radio frequency. In some countries, during periods of maintenance, the facility may radiate a T-E-S-T code () or the code may be removed which tells pilots and navigators that the station is unreliable. In Canada, the identification is removed entirely to signify the navigation aid is not to be used. In the aviation service, Morse is typically sent at a very slow speed of about 5 words per minute. In the U.S., pilots do not actually have to know Morse to
American Morse code a type of distortion called dispersion that gets progressively worse with the length of the cable. Dispersion severely limits the rate that Morse can be sent because of intersymbol interference. For instance, the first transatlantic telegraph cable of 1858 could only sustain a transmission rate of less than 1 word per minute. This interference is worse with American Morse because it has a greater proportion of closely spaced dots than the Gerke code. The Gerke code was adopted as a standard for transmission over cables by the Austro-German Telegraph Union (which included many central European states) at a conference in