Agilent Technologies 8360 L Series, Service Manual

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20. FMBandwidth
(F or B-Series Only)
Description and Procedure
Use this pro cedure to v erify that the RF output p o w er do es not v ary more than a sp ecied
amoun t o v er the sp ecied frequency mo dulation rate frequency range. A low frequency
sp ectrum analyzer with a tracking generator op erates as a net w ork analyzer to measure the
FM atness. Flatness errors asso ciated with the tracking generator and sp ectrum analyzer are
calibrated out of the measuremen t. Flatness errors due to the p o w er splitter and microw a v e
amplier are minimized b y external lev eling at the amplier. The dela y line discriminator is
used to demo dulate the FM from the RF carrier. It also pro vides an input to the sp ectrum
analyzer that is equiv alen t to the tracking generator frequency and prop ortional in p o w er to
the syn thesizer RF output.
The dela y line discriminator is formed b y driving a mixer with a mo dulated carrier in to
the LO p ort, and a dela y ed carrier in to the RF p ort. The dela y is pro duced with a cable of
appro ximately 3 feet in length. With this setup, the mixer resp onds to phase dierences
b et w een the t w o inputs. The cable has a constan t time dela y and, as the carrier frequency is
frequency-mo dulated, a linear phase shift o ccurs b et w een the mixer inputs. Since the mixer
inputs are in quadrature, the mixer op erates as a phase detector that amplitude tracks the
RF input (syn thesizer p o w er) and has an output frequency corresp onding to the FM rate
(tracking generator frequency).
Agilent 8360 P erformance T ests
FM Bandwidth
2-95