Tuning scale for radio receiver - has transparent plate acting as light guide allowing only light scattered from symbols to emerge from front of scale

摘要

The tuning scale has a glass front plate (1) with a transparent card (2) carrying tuning data, e.g. frequencies, behind it. The plate may be acrylic sheeting. A transparent plate (3) is located behind the card and acts as a light guide for light illuminating the scale from a source located e.g. along the top edge of the scale. The refractive index of the transparent plate is less than the refractive index of the glass plate so that total reflection occurs into the glass plate from the boundary between the two plates. Only the light scattered from the symbols emerges through the front of the scale so that the symbols are clearly visible. An opaque dark rear plate (4) is located behind the transparent plate to hide the components inside the receiver. The rear plate has a window through which the scale pointer is visible.