| 摘要 |
<p>A measure of the noise performance of an FDM system can be made by making measurements when the system is carrying traffic. The technique consists of creating a quiet channel in the system, and measuring the noise level in this quiet channel. The tester operates by Teeing off the broad band incoming signal, automatically attenuating the broad band signal to a predetermined level, and then measuring the power leve? in a narrow bandwidth lying within a single channel. The measurement is performed using an automatic attenuator controlled by a feedback loop containing, band pass filters, superhetrodyne detectors, a comparator controlling a counter, which in turn controls the automatic attenuator.</p> |
