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Troubleshooting
Troubleshooting Unlevels
Troubleshooting Unlevels
A leveled output power is obtained comparing a detected voltage with a reference voltage. The
reference voltage is generated using DACs on the A10 ALC and the detected voltage is generated by
coupling off a portion of the RF output signal and converting it to dc using detector diodes. When
the reference and detected levels are the same the integrated output level remains constant. When
the detected and reference levels are not the same, the integrator output ramps either up or down to
increase or decrease the detected level. If the integrator can not get the detected voltage and the
reference voltage to match, an unleveled annunciator is displayed.
The Automatic Leveling Circuit (ALC) uses two detectors and two modulator diodes. The A23
Lowband Coupler/Detector is used for frequencies 2 GHz and below. The A25 Highband
Coupler/Detector is used for all frequencies above 2 GHz. The modulator in the A23 Lowband
Coupler/Detector is used to control the RF amplitude for frequencies 3.2 GHz and below. The
modulator in the A30 Modulation Filter is used to control the amplitude for frequencies above
3.2 GHz.
The RF path must provide a minimum power level to the ALC loop for the ALC loop to work
properly. The minimum power required is slightly higher than the maximum leveled power. The
first step to troubleshooting a leveling problem is to verify the RF path power level.
Troubleshoot and correct any unlock problems before troubleshooting
unleveled problems.
If the unleveled annunciator is on:
1. Verify the signal generator’s amplitude is not set higher than the maximum level specified on
the data sheet. Verify that the signal generator’s RF output is terminated into 50 ohms. If the
unleveled indication turns off after resetting the amplitude or terminating the RF output into 50
ohms, the signal generator is operating correctly. If the unleveled indicator remains on, proceed
to step 2.
2. Using a spectrum analyzer check the RF signal level at the RF output connector.
a. Signal generator and spectrum analyzer setup:
Signal Generator:
• Turn ALC Off
• Set Amplitude to 30 dBm
• Turn Modulation Off
• Turn RF On
• Set Sweep to Frequency
• Set Sweep Type to Step
• Set Start Frequency to 250 kHz
• Set Stop Frequency to 3.2 GHz
• Set Number of Points to 500
Spectrum Analyzer:
• Set Start Frequency to 225 kHz
• Set Stop Frequency to 3.25 GHz
• Set Reference Level to +30 dBm
• Set Display to Max Hold
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