Keysight Technologies N5224A, Руководство по обслуживанию

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Keysight N5224A/25A Service Guide 5-23
Theory of Operation
Receiver Group Operation
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.
The A27 mixer brick sends the EXT TSET DRIVE LO OUT signal to a rear-panel
connector for use with an external test set. This same output connector on the
A28 mixer brick is terminated.
A16 SPAM Board (Analog Description)
The A16 SPAM board contains digital and analog circuitry. For digital
descriptions, refer to “A16 SPAM Board (Digital Description)” on page 5-30 .
In this assembly, the IF signals (A, B, C, D, and R for 4-port models and A, B,
R1, and R2 for 2-port models) from the A24 IF multiplexer board go through a
gain stage where small signals are amplified to ensure that they can be
detected by the analog-to-digital converter (ADC).
All input signals are sampled simultaneously by the ADCs, where they are
converted to digital form. The ADC conversions are triggered by timing signals
from the digital signal processor (DSP) in response to commands from the
central processing unit (CPU). The digitized data is processed into magnitude
and phase data by the DSP and sent to the CPU random access memory (RAM)
by way of the peripheral component interconnect (PCI) bus.
The processed and formatted data is finally routed to the display, and to the
general-purpose interface bus (GPIB) for remote operation. Refer to “Digital
Processing and Digital Control Group Operation” on page 5-27 for more
information on signal processing.
A24 IF Multiplexer Board
This assembly provides pulse modulation capability and routes the IF signal out
through the rear panel connectors for external use and routes external signals
in through rear panel connectors to be included in the signal processing.
In this assembly, on 4-port models, a single reference signal is selected from
R1, R2, R3, and R4 to be sent on to the A16 SPAM. On 2-port models the R1
and R2 reference signals are sent to the A16 SPAM.
The analog IF signals (A, B, C, D, and R for 4-port models and A, B, R1, and R2
for 2-port models) are sent to the A16 SPAM board where they are converted to
digital information.