258 N5511A Phase Noise Test System User’s GuideAM Noise Measurement FundamentalsAmplitude Noise MeasurementUsing an External AM DetectorThe following is an example of how an external detector can be utilized toconnect into the noise inputs of the phase detector module(s) of the N5511A.This is the same as how an AM noise measurement would be traditionallyperformed on the e5500 test set.Figure 11-3 AM detector schematicAM detector specificationsDetector type low barrier Schottky diodeCarrier frequency range 10 MHz to 26.5 GHzMaximum input power +23 dBmMinimum input power 0 dBmOutput bandwidth 1 Hz to 40 MHzAM detector considerations— The AM detector consists of an Keysight 33330C Low-Barrier SchottkyDiode Detector and an AM detector filter (Keysight 70429A K21).— The detector, for example, is an 33330C Low-Barrier Schottky-DiodeDetector. The Schottky detectors will handle more power than the pointcontact detectors, and are equally as sensitive and quiet.— The AM detector output blocking capacitor in the 70429A Option K21,N5500A Option 001, or N5507A prevents the DC voltage component of thedemodulated signal from saturating the system’s low noise amplifier (LNA).The value of this capacitor sets the lower frequency limit of thedemodulated output.The phase noise test set must be DC blocked when using its Noise Input or internal AM detector.The test set will not tolerate more than ± 2 mV DC Input without overloading the LNA. A DC blockmust be connected in series after the AM Detector to remove the DC component. The 70429AOption K21 is designed specifically for this purpose or the internal DC blocking filter in either theN5500A or N5507A may be used.
