A Fourier transform of a segment of a pure 400 Hz tone will produce a spectrum with a sharp peak at 400 Hz. But since the segment is finite, if the tone amplitude is constant, the spectrum will have "sidelobes" that extend over a wide range of frequencies. The sidelobes can be sharply reduced by contouring the amplitude with a "window." An example of the spectrum with and without a window is shown here[50 kb
1. Any device introduced into the atmosphere for producing an appreciable radar echo, usually for tracking some airborne device or as a tracer of wind. 2. A World War II code name for a type of radar-jamming device employed to confuse the operators of enemy radars (also referred to by the code names of rope, chaff , and clutter ). One type of window consists of packages containing thousands of small strips of paperbacked tinfoil which may be dropped from aircraft and balloons, ejected from rockets, and carried within balloons. The packages burst open upon ejection, scattering the tinfoil widely, producing a radar echo which looks like a small shower or a tight formation of aircraft on plan-position-indicator scopes. 3. Any gap in a linear continuum, as atmospheric windows , ranges of wavelengths in the electromagnetic spectrum to which the atmosphere is transparent, or firing windows , intervals of time during which conditions are favorable for launching a spacecraft on a specific mission.