Explanation: An echo box is a specialized test device used to calibrate and tune radar systems. It operates by receiving a pulse from the radar's transmitter, then delaying and re-transmitting a modified version of that pulse back to the radar's receiver. This creates an artificial, controlled "target echo" that allows technicians to test the radar's sensitivity, alignment, and ranging accuracy without needing a real target. Option A is incorrect because the wavelength is determined by the radar transmitter's design. Option C is incorrect as the echo box generates a test signal, rather than just amplifying an existing echo. Option D is incorrect; detection of echo pulses is a function of the radar receiver's processing circuitry. The echo box provides a *simulated* pulse for the radar's receiver to detect.