Table of Contents
Advertisement
5
Absolute Measurement Fundamentals
Tracking Frequency Drift
The system's frequency drift tracking capability for the phase lock loop
measurement is directly related to the tuning range of the VCO source being
used. The system's drift tracking range is approximately 24% of the peak
tuning range (PTR) of the VCO.
This is the frequency range within which the beatnote signal created by the
test set's phase detector must remain throughout the measurement period. In
addition, the beatnote signal must remain within the system's Capture Range
(5% of the PTR) during the time it takes the system to calibrate and lock the
phase lock loop.
The stability of the beatnote is a function of the combined frequency stability
of the sources being used for the measurement. If beatnote drift prevents the
beatnote from remaining within the Capture Range long enough for the system
to attain phase lock, the computer informs you by displaying a message. If the
beatnote drifts beyond the drift tracking range during the measurement, the
computer stops the measurement and inform you that the system has lost lock.
Evaluating beatnote drift
The Checking the Beatnote section included in each phase lock loop
measurement example in this chapter provides a procedure for adjusting the
beatnote to within the Capture Range set for the measurement. If you have not
done so already, verify that the beatnote signal can be tuned to within the
Capture Range and that it will remain within the range.
Continue to observe the beatnote and verify that it will not drift beyond the
drift tracking range (24% of the PTR) during the measurement period. The
length of the measurement period is primarily a function of the frequency
offset range specified for the measurement (Start to Stop Frequency).
116
PTR= VCO Tuning Constant X Voltage Tuning Range
Agilent E5505A User's Guide
Advertisement
Table of Contents
