In
telecommunication, a
neutral direct-current telegraph system is a telegraph
system in which (a) current flows during marking intervals and no current flows during spacing intervals for the
transmission of signals over a
line, and (b) the direction of current flow is immaterial.
Synonyms single-current system, single-current transmission system, single-Morse system.
Source: from Federal Standard 1037C and from MIL-STD-188