Receiver Group Operation; A46-A49 35-Db Receiver Step Attenuators; A37 Reference Mixer Switch; A27 And A28 Mixer Bricks - Keysight N5224A Service Manual

PNA Series Microwave Network Analyzers
N5224A and N5225A

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
receiver functional group for 2-port and 4-port models.
In this section the following assemblies are described:
• A46–A49 35-dB Receiver Step Attenuators
•

A37 Reference Mixer Switch

•

A27 and A28 Mixer Bricks

• A24 IF Multiplexer Board
• A16 SPAM Board (Analog Description)
A46–A49 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 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.
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 signal that is 7.438 MHz higher than the source incident
signal to produce a 7.438 MHz IF signal. This synthesized LO comes from the A25 HMA26.5 (via the A26
splitter for 4-port models).
At frequencies below 53 MHz, the IF is set to 0.826 MHz.
The analog IF signal is sent to the A24 IF multiplexer board where it is amplified and then sent to the A16
SPAM board.
Service Guide N5225-90001
and Figure 5-7 on page 5-25
Theory of Operation
Receiver Group Operation
are simplified block diagrams of the
5-21