Chapter 8 187
Hardware Options
Overview and Verification of Option 123, Microwave and Millimeter Preselector Bypass
Overview and Verification of Option 123,
Microwave and Millimeter Preselector Bypass
Overview of Option 123 in the E4440A, E4443A, or
E4445A
Option 123 provides an unpreselected input mixer path for the E4440A,
E4443A and E4445A spectrum analyzers in the 3.05 to 26.5 GHz
frequency range. This allows a signal path with a wider bandwidth and
less amplitude variability, which is an advantage when doing
modulation analysis and broadband signal analysis. The disadvantage
is that, without the preselector, image signals will appear.
Functionality
In normal instrument operation, when operating above 3.05 GHz, a
preselector precedes the input mixer (see Figure 8-9 below). This
preselector is part of the RYTHM circuitry, and 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. With Option 123,
the RF path can be routed via RF switches to an alternate highband
(3.05 - 26.5 GHz) mixer that does not incorporate the tunable bandpass
filter.
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