Agilent Technologies N5242A, Service Manual

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Service Guide N5242-90001 5-21
PNA Series Microwave Network Analyzers Theory of Operation
N5242A 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 5-25 and Figure 5-7 on page 5-26 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 (Optional)
• 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 (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 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 channels are needed.
For frequencies at or above 53 MHz, the test signals (channels A, B, C, and D for 4-port
models and A and B for 2-port models) and the reference signals (channels 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 7.606 MHz higher than the source incident signal to produce a 7.606 MHz IF
signal. This synthesized source comes from the A21 HMA26.5 (via the A22 splitter for
4-port models).
At frequencies below 53 MHz, the IF is set to 2.535 MHz.