| 摘要 |
PURPOSE:To detect occurrence of overmodulation by adding an RF signal subject to digital modulation with a data signal able to detect a transmission code error as one channel, utilizing the channel, detecting the code error after transmission and raising warning when errors of a prescribed error rate or over are detected. CONSTITUTION:A mixer 4 mixes a frequency multiplex signal 1 and an output of a digital modulator 3 and a carrier frequency and the modulation degree of digital modulation are set so that an output of the digital modulator 3 does not give effect on the frequency multiplex signal 1. Then a data signal is demodulated by a digital demodulator 9 at a receiver side, and when overmodulation takes place in the stage of an optical signal, the data signal might have been effected and a code error takes place when much effect is caused. Thus, the occurrence of overmodulation is detected by detecting a code error by an error detector 10. |
