power, while switching its current on and off for portions of a time interval. The percentage of time that the current is on during the time interval is referred to as the "duty cycle."
The duty cycle of the microwave oven is generally implemented by electromechanical relays in conjunction with the controls of the microwave oven. The relays provide economies of scale for a manufacturing effort but they do not adequately provide competent electrical current switching.
Magnetron power output is proportional to its cathode current. In amplitude modulation, the cathode current is adjusted to control the instantaneous magnetron output. The instantaneous magnetron current is controlled either by varying the level of high voltage to the magnetron or by changing the magnetic field intensity in the magnetron.
Attempts in the past havein the light back-scattered from the screen, as well as in rear projection, in other words when viewing the image as the transmission of an image projected on the back of the screen. The size of the image speckles and the degree of intensity modulation depend on the fineness of the surface roughness or the density of scatter centers in a volume-scattering screen and the viewing distance and viewing angle relative to the screen. Small speckles develop in coarsely structured surfaces, and large speckles develop in finely structured surfaces. In the case of reflecting surfaces with surface roughnesses far below the wavelength of the light, the speckles are so large that they are no longer resolved as such by the eye.
The image noise caused by the speckles, which