Keysight Technologies N5221A, Service Manual, Page: 146 / 368

5-22 Keysight N5221A/22A Service Guide
Theory of Operation
Receiver Group Operation
5-
than the source incident signal to produce a 7.438 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 0.826 MHz.
The analog IF signal is sent to the A20 IF multiplexer board where it is
processed and then sent to the A12 SPAM board.
The A23 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
A24 mixer brick is terminated.
A20 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, the R1, R2, R3, and R4 reference signals
are combined to create one reference signal, R. On 2-port models the R1 and
R2 reference signals are not combined.
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 A12 SPAM board where they are converted to
digital information.
Rear Panel Interconnects
The A20 IF multiplexer board includes the following rear panel interconnects.
PULSE I/O
A DB-15 female connector. Pin assignments are listed in
Table 5-4
.
Table 5-4 PULSE I/O Connector Pin Assignments
DB-15 Female Connector
Pin Name Description
1 IFGateAin IF pulse gate input A (TTL)
2 IFGateBin IF pulse gate input B (TTL)
3 IFGateCin IF pulse gate input C (TTL)
4 IFGateDin IF pulse gate input D (TTL)
5 IFGateRin IF pulse gate input R (TTL)