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Assembly Descriptions and Block Diagrams
IF Section
IF Section
This section applies to all 8590 E-Series and L-Series spectrum
analyzers, 8591C cable TV analyzers, and 8594Q QAM analyzers, and
describes the operation of the IF section assemblies and the A16
processor/video assembly. The related operation of the A7 analog
interface assembly and the A8 Power Supply are also described.
Figure
9-1
illustrates the assembly descriptions in this section.
The A15 motherboard pin designation of related assemblies along the
IF signal path are detailed on
Figure
9-1. Refer to
Chapter 5
for more
information about the connection of analyzer assemblies to the
motherboard.
A11 Bandwidth Filter
The A11 bandwidth filter assembly contains two synchronously tuned
LC filter poles and two synchronously tuned crystal filter poles. Buffer
amplifiers provide isolation for each filter pole.
Eight IF bandwidths, from 1 kHz to 3 MHz, can be selected in a 1, 3, 10
sequence. The desired IF passband, or resolution bandwidth, is
produced by either a four-pole LC bandpass filter or a four-pole crystal
bandpass filter. The A13 bandwidth filter assembly is identical to the
A11 assembly and provides two of the four filter poles. The LC
bandpass filters provide the 100 kHz to 3 MHz bandwidths, and the
crystal bandpass filters provide the 1 kHz to 30 kHz bandwidths.
When a bandwidth is selected, the A7 analog interface assembly
interprets the A16 processor/video assembly commands and produces
the corresponding bandwidth control currents. The A7 assembly
produces a bias voltage (BW5) to select LC or crystal mode, and a
bandwidth control current for either the LC filters (BW7) or the crystal
filters (BW6).
Bandwidth errors are corrected by the
self-calibration
CAL AMPTD
routine. Refer to
Chapter 13
for a description of
.
CAL AMPTD
The resolution bandwidths are normally coupled to the frequency span
of the analyzer for an optimum ratio of span to resolution bandwidth.
Sweep time is also coupled to both resolution bandwidth and span for
optimum amplitude response. The resolution bandwidth, sweep time,
and span can be set independently.
Chapter 9
373
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