The 8445B Tracking Preselector contains a YIG filter which tracks the tuned frequency of the analyzer over the range of 1.8 to 18GHz. The preselector suppresses the image and multiple responses which result from harmonic mixing. The YIG filter is electronically tuned by sweep voltage and band code signals from the analyzer. Tracking filter 3 dB bandwidth is typically 20 to 45MHz. Tracking filter skirt roll-off is nominally 18 dB/octave. Insertion loss for the low-pass filter (DC to 1.8GHz) is <2.5 dB. Insertion loss for the tracking filter is (1.8 to 12GHz) <8 dB and (12 to 18GHz) <10 dB.