DUMMY LOAD cial functions. It does not have provisions for attaching a cable. Dummy receptacles normally have no inserts or contacts present and are usually simple receptacle shells. DUMMY LOAD A device or any electronic circuit that provides a simulation of the normal input or output of a circuit or a system under test. DUNNAGE Lumber, strapping, nails, or other material used to secure and protect lading. DUPLEX CIRCUIT A circuit that permits simultaneous transmis- sion in both directions. DUPLEXER A device that permits the simultaneous use of a trans- mitter and a receiver in connection with a common element such as an antenna system. DUPLICATE ORIGINAL A replica of an engineering drawing or digital data file created to serve as the official record of the item when the original has been lost. DUTY CYCLE (1) The ratio of the sum of all pulse durations to the