134 Keysight CXG, EXG, and MXG X-Series Signal Generators Service Guide
Troubleshooting
Unleveled Issues
Unleveled Issues
An Automatic Leveling Control (ALC) loop in the instrument provides leveled
output power. The ALC loop is a feedback control system that monitors the RF
power and maintains it at the user-selected level. The RF path must provide a
minimum power level to the ALC loop for the ALC loop to work correctly. The
minimum required power is slightly higher than the instrument maximum
output power level.
A leveled output power is obtained by comparing a detected voltage with a
reference voltage. The detected voltage is generated by coupling off a portion
of the RF output signal and converting it to a DC voltage using detector
diodes. The reference voltage is generated using calibrated DAC’s. When the
reference and detected levels are not the same, the ALC integrator output
ramps up or down, to increase or decrease the detected level. If the integrator
cannot achieve a match between the detected and reference voltages an
unleveled indicator is displayed.
The assemblies inside of the ALC loop vary by model number as shown in
Table 6-2.
The more assemblies within the ALC loop, the more complicated it becomes to
determine what might be causing an unleveled condition. Refer to Chapter 13,
“Block Diagrams” for information on where the ALC detectors and modulators
are located in the A3 RF and A7 Micro-Deck assemblies.
Before troubleshooting any unleveled condition verify that there are no
unlocked errors or Self Test failures. If there are any unlocked errors or Self
Test failures resolve them before proceeding with any unleveled condition
troubleshooting.
To start troubleshooting an unlevel condition determine under what conditions
the unleveled is occurring. Is it only:
1. When tuned to certain frequencies.
2. When the power level is set to certain levels.
3. When I/Q modulation is turned on (N5166B, N5172B, N5182B).
Table 6-2 Assemblies Within the ALC Loop
Model Numbers Assemblies within ALC Loop
N5171B, N5181B A3 RF Assembly
N5166B, N5172B
N5182B
A2 Vector BBG Assembly
A3 RF Assembly
N5173B, N5183B A3 RF Assembly
A7 Micro-Deck Assembly
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