108 E8257D/67D, E8663D PSG Signal Generators Service Guide
Troubleshooting
Troubleshooting Unlevels
Troubleshooting Unlevels
A leveled output power is obtained by 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 A8 Output Board 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 (if Option 007 is installed, you can
use ramp sweep)
— Set Start Frequency to 250 kHz
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