| 摘要 |
A dual locked loop is disclosed comparing preferably a GPS signal with an E1 signal and the E1 signal with the output of the loop. The GPS signal is low pass filtered to provide a low pass filtered GPS versus E1 signal that is us ed as a calibration for a closed loop having a second low pass filter for filtering the comparisons of the E1 and the output signal. By appropriately selecting the filter parameters, the output stability can track the stabilit y of the local oscillator driving the NCO for short term stability, the medium term stability of the E1 signal and the long term stability of the GPS signa l.
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