Theoryof Operation- 4g4A/494ApService,Vot.1

Directional Filter

The DirectionatFitter (FL10)couptesthe 2072MHz signalto the 2nd Convertervia low-passand band-passfilters FLl1 and FL14. As mixing products iass through FL16, they induce a selected current into a one-wavelengthdistributed dng, which couples the 2072MHzlF signatout to the tow-passfitterFLl t. The remainderof the intermodulationproducts pass on through since the ring is excited only with ZiOZZl/r{z signals. The bandwidth of this DirirctionalFitter is approximately45 MHz. The unfiltered signals are passedon to the Diplexer.

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2072MHz lF Filters

The 2072MHz signal, from the Directional Fitter, passesthrougha 4.5 GHz Low-PassFilter{FL11}.The signal is then sent througha 15 MHz band-passfilter (FL14) which reiects intermodulationproducts either side of the 2072MHzlF.

Diplexer and Filter

The Diplexer (A14)passes the 829 MHz tF signal from the mixer outputthrougha low-passfilter (FL15)to the 2nd Converter.The Diplexerand DirectionalFilter provide a broadbandimpedancematch to the l st Mixer lF port. This match contributesto thE overall flatn€ss and frequencyresponseof the analyzer.

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Tektronix 494AP service manual