RDF is probably radio direction finding (without looking at the exact question).
Duty cycle-"Operating parameters of a cell or battery including factors such as charge and discharge rates, depth of discharge, cycle length, and length of time in the standby mode."
"The ratio of "on" time to "off" time for an electronic component or signal. In a power system duty cycle is typically used in reference to the semiconductor switch (in PWM controlled systems) or clock signal."
Haven't looked at the exact question but I hope those are helpful.
Virginia Fone Net #72