| 摘要 |
For measuring the group delay of amplitude modulated transmitters a variable measurement frequency is modulated by a fixed frequency so as to obtain the sum and difference frequencies which are sent to the input of the transmitter under test; the two waves corresponding to the same side-band are obtained at the transmitter output, are frequency shifted, filtered and detected to give their beat, filtered again to obtain only the beat at a frequency twice the modulation frequency; and said beat is compared with a signal of the frequency but coherent with the modulating signal, the comparison providing a direct voltage component which is a linear function of the group delay of the side-band corresponding to the measurement frequency. The invention also concerns the apparatus for realizing the method, comprising also the known units allowing to measure the amplitude of each side band. |
