Sure. An echo box is a tuneable resonant cavity. it hooks into the radar antenna/ feedline which is waveguide. You tune it to resonance as indicated by a huge overload condition on the radar scope, or by a huge blip on a test oscilloscope. it is a 'quick' indicator, relatively speaking of transmitter power and receiver sensitivity. You log the readings you get, and over time, deterioration indicates 'something has changed.' It can be something wrong in the waveguide, something wrong (moisture?) in the echo box, or trouble in either the receiver or transmitter.
Tuned cavities are analogous to blowing across a bottle. The size of the cavity, which is changed by a moveable plunger, determines the frequency at which the cavity is resonant.
