Keysight Technologies N5247B, Service Manual

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Keysight N5247B Service Guide 5-53
Theory of Operation
Receiver Group Operation
Receiver Group Operation
The receiver group measures and processes the input signals into digital
information for processing and eventual display. Figure 5-18 on page 5-57 and
Figure 5-19 on page 5-58 are simplified block diagrams of the receiver
functional group for 2-port and 4-port analyzers respectively.
In this section the following assemblies are described:
— A46–A49 50-dB Receiver Step Attenuators (Optional)
— A37 Reference Mixer Switch
— A27 and A28 Mixer Bricks
— A24 IF Multiplexer Board
— A16 SPAM Board (Analog Description)
A46–A49 50-dB Receiver Step Attenuators (Optional)
A step attenuator is placed in the signal path of each of the A, B, C, and D
receiver inputs for 4-port models and A and B receiver inputs for 2-port
models.
These 50-dB step attenuators provide power control for the input signals to the
mixer bricks. They are electro-mechanical step attenuators that provide 0 to
50 dB of attenuation in 10-dB steps. These attenuators are controlled by the
A21 CPU board.
A37 Reference Mixer Switch
The A37 reference mixer switch is placed in the R1 reference signal path
allowing this reference signal to be switched in and out of the signal path when
an external mixer is being used in test configuration.
An external mixer is placed in measurement configuration between
REFERENCE 1 SOURCE OUT and RCVR R1 IN where there would normally be a
front panel jumper. The A37 reference mixer switch can then be used to switch
this external mixer in and out of the measurement configuration without having
to manually connect/disconnect the external mixer and remove/replace the
front panel jumper.
A27 and A28 Mixer Bricks
Each of these assemblies contain four identical amplifiers, mixers, and filters
for a total of eight of each. For 2-port models, only the A27 mixer brick is
present; the A28 mixer brick is omitted since only four receivers are needed.
Refer to
the NOTE notice on page 5-1 . For frequencies at or above 53 MHz, the
test signals (receivers A, B, C, and D for 4-port models and A and B for 2-port
models) and the reference signals (receivers R1, R2, R3, and R4 for 4-port
models and R1 and R2 for 2-port models) are mixed with a synthesized LO