HP 3048A Operating Manual page 178

Table 3-25. Numbered Error Messages (11 of 17)
1 1 DC offset too large. Waveform does not cross 0 volts. This error occurs when the
system is measuring the Phase Detector Calibration Constant and one of the following
conditions exist.
1. The dc offset is greater than the peak beatnote voltage due to a large dc offset or a
low beatnote level.
2. The beatnote frequency is much lower than expected and only the top or bottom
portion of a sine wave peak is actually measured.
Action:
1. Observe the beatnote on the time record of the HP 3561A or on an oscilloscope
connected to the AUX MONITOR port of the HP 11848A.
Verify that the beatnote amplitude is correct for the signal level at the R input port
on the HP 11848A. Figure 3-36 shows the relationship between the beatnote level
and the level at the R input port.
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- 1 5 - 5 +5 +15
R PORT SIGNAL LEVEL (dBm)
Figure 3-36. Beatnote Level Relative to the Signal Level at the R Port.
2. Verify that the phase detector DC offset is < 30 mV (< 50 mV if you are using the
1.2 to 1.8 GHz Phase Detector).
3. If the HP 3048A was not configured to measure the VCO Tuning Constant, verify
that the entered value is within a factor of 2 of the VCO's actual Tuning Constant.
A procedure for verifying the VCO's Tuning Constant is contained in Estimating the
Tuning Constant in Chapter 3 of this manual.
4. When the system measures the Phase Detector Constant, the beatnote frequency
should be set to approximately 10% of the Peak Tuning Range (PTR) set for the
measurement. If it is not, verify the VCO Tuning Constant and Voltage Tuning Range
entered for the measurement.
rev.l2JUL88
Signal Source Applications 3-131