| 摘要 |
PURPOSE:To reduce an occupied band width of a transmitted radio wave into a specified width or below by providing an amplitude limit circuit to the pre- stage of a high frequency oscillating modulator and a filter connected to the post-stage of the said limit circuit and cutting off the highest frequency of a normal video signal frequency component. CONSTITUTION:A video input signal (a) enters an amplitude limit device 1, and the output is proportional until the input amplitude reaches a certain value and becomes constant when the input amplitude exceeds the value. The video signal of the constant amplitude enters a low pass filter 2. A cut-off frequency fc of the filter 2 is selected to the highest frequency of normal state and frequencies being the fc or over are cut off. Harmonic noise and high frequency noise are eliminated by the filter 2. An output of the filter 2 enters a video amplifier 3, whose gain is set so that a specified occupied frequency band width is obtained at a high frequency oscillating modulator 4 of the next stage. Then, a high frequency signal (e) to be modulated whose occupied frequency band width is kept within the specified value is outputted from the modulator 4 and irradiated from an antenna 5. |
