| 摘要 |
A test system is used to test a modem whose modulator is constituted by a multivibrator which during normal operation produces two frequencies f1, f2 in response to the data signal and which is connected to a transmission filter. In response to a test control signal, the multivibrator is modified to supply two test frequencies f'1=nf1, f'2=nf2, n being substantially equal to the ratio Fo/fo, Fo being the average value of the frequencies received by the modem during normal operation, fo being the average value of the frequencies f1, f2; at the same time the transmission filter is modified to transmit the two frequencies f'1, f'2 in response to the test control signal.
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