Chapter 8 197
Hardware Options
Overview and Verification of Option 123, Microwave and Millimeter Preselector Bypass
Overview of Option 123 in the E4446A, E4447A, or
E4448A
Functionality
During normal operation of the PSA, when operating above 3 GHz, a
preselector precedes the input mixer. This preselector is part of the
SBTX and RYTHM circuitry. It is basically a tunable bandpass filter
which prevents signals away from the frequency of interest from
combining in the mixer to generate in-band spurious signals. The
consequences of using this preselector filter are its limited bandwidth,
amplitude and phase ripple in its passband, and amplitude and phase
instability due to center frequency drift.
Option 123 adds the > 3.05 GHz to 50 GHz unpreselected highband
mixer path to the E4446A, E4447A, and E4448A millimeter wave band
instruments. The block diagram is shown in Figure 8-11. This option
adds the millimeter unpreselected mixer, the 50 GHz coax transfer
switch and the coax IF switch. The option driver board provides control
of the switches, the unpreselected bias board control, and storage for
the calibration factors that compensate the unpreselected path flatness.
Figure 8-11 Block Diagram for 50 GHz Option 123 Instruments
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