108 E8257D/67D, E8663D PSG Signal Generators Service GuideTroubleshootingTroubleshooting UnlevelsTroubleshooting UnlevelsA leveled output power is obtained by comparing a detected voltage with areference voltage. The reference voltage is generated using DACs on the A10ALC and the detected voltage is generated by coupling off a portion of the RFoutput signal and converting it to dc using detector diodes. When thereference and detected levels are the same the integrated output level remainsconstant. When the detected and reference levels are not the same, theintegrator output ramps either up or down to increase or decrease thedetected level. If the integrator can not get the detected voltage and thereference voltage to match, an unleveled annunciator is displayed.The Automatic Leveling Circuit (ALC) uses two detectors and two modulatordiodes. The A23 Lowband Coupler/Detector is used for frequencies 2 GHz andbelow. The A25 Highband Coupler/Detector is used for all frequencies above2 GHz. The modulator in the A8 Output Board is used to control the RFamplitude for frequencies 3.2 GHz and below. The modulator in the A30Modulation Filter is used to control the amplitude for frequencies above3.2 GHz.The RF path must provide a minimum power level to the ALC loop for the ALCloop to work properly. The minimum power required is slightly higher than themaximum leveled power. The first step to troubleshooting a leveling problem isto verify the RF path power level.Troubleshoot and correct any unlock problems before troubleshootingunleveled problems.If the unleveled annunciator is on:1. Verify the signal generator’s amplitude is not set higher than the maximumlevel specified on the data sheet. Verify that the signal generator’s RFoutput is terminated into 50 ohms. If the unleveled indication turns offafter resetting the amplitude or terminating the RF output into 50 ohms,the signal generator is operating correctly. If the unleveled indicatorremains on, proceed to step 2.2. Using a spectrum analyzer check the RF signal level at the RF outputconnector.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 canuse ramp sweep)— Set Start Frequency to 250 kHz
