Keysight N9038A, Service Manual

Page: 164 / 745

164 Keysight N9038A MXE Service Guide
RF Preselector Section
RF Preselector Section Purpose
RF Preselector Section Purpose
The assemblies covered in this section are responsible for preselecting input
signals below 3.6 GHz. This is required for the accurate measurement of
electromagnetic emissions according to many of the standards prescribed for
this type of testing. Without this preselection of the input signal the presence
of broadband signals could overload the 1st mixer of the instrument making it
impossible to accurately measure low level signals.
RF Preselector Section Description
There are two different signal paths that the user can select through this
section of the instrument:
— Conducted Filter Path - 20 Hz to 30 MHz
— Radiated Filter Path - 30 MHz to 3.6 GHz
The components of the RF Preselector section discussed in this chapter are:
— A21 RF Preselector Input Assembly
— A22 Radiated Filter Assembly
— A24 Conducted Filter Assembly
RF Preselector Section Signal Paths
Conducted Filter Path - 20 Hz to 30 MHz
The input signal is routed to the SW2 Transfer switch, where it could either
be directed through the RF Preselector section of the instrument or bypass
it.
When routed through the RF Preselector section the input signal first goes
to the A21 RF Preselector Input assembly where it is sent through a low
pass filter before it is routed to the A24 Conducted Filter assembly.
Refer to Chapter 15, “Block Diagrams.” .
Refer to Chapter 15, “Block Diagrams.” .