| 摘要 |
PROBLEM TO BE SOLVED: To execute the loop-back of a self station, even without a signal interrupt function from an opposite station by respectively frequency-converting a loop back signal from a transmission side and a receiving signal into the receiving signals of first and second intermediate frequency bands, attenuating the receiving signal of the second intermediate frequency band, frequency- converting the loop back signal of the first intermediate frequency band to suppress unwanted waves and extracting its at a prescribed level. SOLUTION: At the time of the loop-back of a self station, a signal outputted from an RF amplifier 13 is added to the RF amplifier 13 with a transmission side branch part 14 and a reception side branch part 17 to be amplified. After that, it is mixed with a station originating signal by a second frequency converter 19, and the loop back signal IFf1 is extracted so as to be added to a selective band filter 20. The selective band filter 20 permits the loop back signal IFf1 to pass through. However, since the signal reception side IF signals (IFf2) is provided with a preventing function, the return signal IFf1 passed through the filter, amplified by an if amplifier 21, and after that, added to a third frequency converter 22. |
