DECOLLIMATION DECARBURIZATION The loss of carbon from the surface of a ferrous alloy as a result of heating in a medium that reacts with the carbon. DECAY TIME The time taken by a quantity to decay to a stated fraction of its initial value. The fraction is commonly 1/e, where e is the base of natural logarithms (1/e = 0.37) DECAY TIME, PULSE The time required for the instantaneous amplitude of a pulse to go from 90 to 10% of a peak value. DECEPTION, DEVICE A device that works to confuse unfriendly signals so as to make them either unusable or misleading. DECEPTION, ELECTRONIC The deliberate radiation, reradia- tion, reflection, or absorption of electromagnetic waves in a manner intended to mislead an enemy in the interpretation of data received by an electronic control system. DECIBEL (dB) Dimensionless unit for expressing the ratio of two values, the number of decibels being 10 times the logarithm to the base 10 of a power ratio, or 20 times the logarithm to the base 10 of a voltage or current ratio.