HP 3048A Operating Manual page 176

Table 3-25. Numbered Error Messages (9 of 17)
Measured beatnotes depict non-linear VCO Tuning Constant. (Error 7 only occurs
when the HP 3048A has been configured to Measure the VCO Tuning Constant.)
The values shown on the display represent the measured beatnote frequencies for four
tune voltage settings. The tune voltage settings are each derived as a percentage of the
entered Voltage Tuning Range of the VCO (-45%, -15%, +15%, +45%) relative to the
entered Center Voltage of the VCO Tuning Curve. For Example:
Voltage Tuning Range of VCO = ±10V
Center Voltage of VCO Tuning Curve = OV
Tune Voltage Settings = -4.5V, -1.5V, +1.5V, +4.5V.
Refer to the HP 3048A Reference Manual Instrument Parameters in Chapter 2,
Measurement Definitions for system requirements for VCO linearity.
Note that between the four measured frequency values shown on the display, three
frequency range intervals are created. (For example, the measured values 95 Hz, 98.2 Hz,
101.2 Hz, 105 Hz produce the following intervals: Interval 1 = 3.2 Hz, Interval 2 = 3 Hz
and Interval 3 = 3.8 Hz.)
Action:
1. This error will occur if a Tuning Voltage Range of ±10 volts has been defined for a
source with calibrated DC FM, and the HP 3048A is configured to Measure the VCO
Tuning Constant rather than to Compute it. Refer to the HP 3048A Reference Manual
"Enhanced Tuning" in the Instrument Parameters section of Chapter 2, Measurement
Definitions for details on extending the Tuning Voltage Range of calibrated DC FM.
2. If Interval 2 (described above) > > 1, and Interval 2 > > 3, then:
Reduce the value entered for the Voltage Tuning Range of the VCO and then initiate
a New Measurement.
3. If there appears to be too little or no change between the measured frequency val­
ues (Intervals 1, 2, and 3ss0) then :
• Check the Tune Voltage cable connections.
• Verify that the VCO's tuning is enabled.
• Perform the Estimating the Tuning Constant procedure provided in Chapter 3
of this manual to verify the tuning response of the VCO and check that the
entered VCO Tuning Constant is within a factor of 2 of the actual value.
• Refer to the HP 3048A Reference Manual Instrument Parameters in Chapter 2,
Measurement Definitions for Tuning Constant linearity requirements.
• Verify that the beatnote is tuned to within the Capture Range for the
measurement.
rev.l2JUL88
Signal Source Applications 3-129