Keysight EXG and MXG X-Series Signal Generators User’s Guide 427TroubleshootingRF OutputSignal Loss While Working with a MixerTo fix signal loss at the signal generator’s RF output during low–amplitude coupled operation witha mixer, add attenuation and increase the RF output amplitude.The figure at right shows aconfiguration in which the signalgenerator provides a lowamplitude signal to a mixer.The internally leveled signalgenerator RF output (and ALClevel) is–8 dBm. The mixer is driven withan LO of +10 dBm and has an LO–to–RF isolation of 15 dB. Theresulting–5 dBm LO feedthrough enters thesignal generator’s RF outputconnector and arrives at the internal detector.Depending on frequency, it is possible for most of this LO feedthrough energy to enter the detector.Because the detector responds to its total input power regardless of frequency, this excess energycauses the ALC to reduce the RF output. In this example, the reverse power across the detector isactually greater than the ALC level, which can result in loss of signal at the RF output.To avoid damaging or degrading the performance of the signal generator,do not exceed 33 dBm (2W) maximum of reverse power levels at the RFinput. See also Tips for Preventing Signal Generator Damage onwww.keysight.com.MixerLOALCLevel =−8 dBmRFLevelSignal GeneratorOutput ControlDetectormeasures−8 dBmALC levelDetectormeasures−5 dBmreversepowerLOFeedthru= −5 dBmRFOutput= −8LO Level= +10 dBmIFEffects of Reverse Power on
