What is meant by the error message, "CAL GAIN FAIL" during the internal amplitude self-calibration on the 8590 Series Spectrum Analyzer?
This failure occurs during the amplitude self-calibration when the firmware routine tries to set the 300 MHz, -20 dBm calibrator signal to the proper level. The firmware routine changes the reference level calibration digital-to-analog converter (DAC) on the analog board until the desired power level is achieved. The DAC range is from 0-255 bits and the incremental change is ~0.14 dB per DAC count. The output of this DAC drives a variable gain amplifier on the 3rd converter. If there are losses in the analyzer, the DAC will go to the maximum of 255 and will not be able to set the calibrator level to -20 dBm. Therefore, the "CAL GAIN FAIL" message appears. Usually, the losses are caused by something in the RF section.