Agilent Technologies HP 8642A/B Specifiche Scaricare il pdf (Pagina 422)

Table 8-3. Reference Messages (6 of 7)

(cont'd)

Action:

The key factor for having a good match between the measured loop suppression

and the theoretical is the accuracy of the Phase Detector Constant and the

VCO Tuning Constant. Abort the measurement and verify that these calibration

constants are accurate.

a. Verify that the VCO Tuning Constant entered for the measurement is within a factor

of 2 of the VCO's actual tuning constant. (A procedure for evaluating the sensitivity

of your VCO is provided in Estimating the Tuning Constant in Chapter 3 of the

Operating Manual.)

b. Verify the Phase Detector Constant by connecting an oscilloscope to the AUX

MONITOR port on the HP 11848A. The peak voltage at the AUX MONITOR port

should equal the Phase Detector Constant measured by the system.

If the calibration constants are accurate, begin a New Measurement and proceed to

the hardware Connect Diagram. Observe the beatnote signal on the HP 3561A using

the Checking the Beatnote procedure provided in each PLL measurement example in

Chapter 3 of the Operating Manual.

a. Verify that the beatnote signal is sinusoidal (or triangular if the input signals are

square waves or if the levels of both input signals are > +15 dBm).

b. Verify that all even harmonics are < —30 dBc on the beatnote and < —20 dBc on

the input signals.

c. Check for injection locking.

Check for noise that exceeds the small angle line. (Refer to Evaluating Noise Above

the Small Angle Line in Chapter 3 of this manual for a procedure.)

3. If the beatnote signal meets the preceding tests, proceed with a New Measurement. If

this same message is displayed again, press the Suppr. Plot key to access a plot of the

PLL suppression curve.

a. If the measured curve does not match the theoretical because it is noisy, press

to proceed with the measurement using the theoretical PLL

Proceed Theor

suppression data. The accuracy of the measurement results will be unverified but

the results may help you to identify the source of the problem.

b. If the measured curve does not match the theoretical because it has high peaks

and the Accuracy Spec. Degradation is < 2 dB, press Proceed w/Adj to proceed

with the measurement using an adjusted PLL suppression. The accuracy of the

results will be degraded by 2 dB within a decade of the PLL bandwidth for the

measurement. Figure 8-8 shows PLL bandwidth relative to the Peak Tuning Range

(PTR) set by the VCO source. (Refer to Chapter 2, Measurement Definitions for

further information about the PTR.)

8-26 Reference Messages

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Agilent Technologies HP 8642A/B Specifiche Pagina 422