| 摘要 |
PURPOSE:To reduce power consumption by extracting the deviation frequency component of FSK modulated wave by means of two narrow-band filters, and deciding on the presence of FSK modulated wave when both of the said filters extract a deviation frequency component to stop transmitting a carrier in case FSK modulated wave is absent. CONSTITUTION:The spectrum of FSK modulated wave includes, as shown by a curve (a), and deviation frequencies f1, f2 deviated from the center frequency f0 by DELTAf, however, a non-modulated wave includes only the center frequency f0. Therefore, by making the pass-band characteristics of the narrow-band filter 1, 2 as broken-line curves (c), (d), the deviation frequencies f1, f2 can be extracted. Detection parts 3, 4 respectively detects an output signal from the filters 1, 2 by means of level-detection or others, and an identification part 5 decides on the presence of FSK modulated wave at a time wave both detection parts 3, 4 supply respective detection signals. And during a time when the modulated wave is absent, the transmission of carrier is stopped, to prevent a useless consumption of power.
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