Keysight Technologies N5221A, Руководство по обслуживанию, Страница: 145 / 368

Keysight N5221A/22A Service Guide 5-21
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 5-6 on page 5-24 and
Figure 5-7 on page 5-25 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:
— A42–A45 35-dB Receiver Step Attenuators
— A33 Reference Mixer Switch
— A23 and A24 Mixer Bricks
— A20 IF Multiplexer Board
— A12 SPAM Board (Analog Description)
A42–A45 35-dB Receiver Step Attenuators
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 35-dB step attenuators provide power control for the input signals to the
mixer bricks. They are electro-mechanical step attenuators that provide 0 to 35
dB of attenuation in 5-dB steps. These attenuators are controlled by the A17
CPU board.
A33 Reference Mixer Switch
The A33 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 A33 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.
A23 and A24 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 A23 mixer brick is
present; the A24 mixer brick is omitted since only four receivers are needed.
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 source signal that is 7.438 MHz higher