Chapter 9 359
Assembly Descriptions and Block Diagrams
RF and LO Section for 8590L, 8591E, and 8591C Spectrum Analyzers
RF and LO Section for 8590L, 8591E, and
8591C Spectrum Analyzers
This section describes the operation of the A3 front-end assembly and
the A25 counterlock assembly for the 8590L and 8591E spectrum
analyzers and 8591C cable TV analyzers. The related operation of the
A7 analog interface assembly and the A9 Third Converter are also
described. Each block of text describes an analyzer assembly designated
by its reference designator. For details about the operation of the
8590L, 8591C, and 8591E RF section, refer to Figure 9-2, located at the
end of this chapter.
The RF front-end section uses triple conversion to convert RF signals to
the final 21.4 MHz IF frequency.
J1 Input Connector
The analyzer RF section receives input signals via a 50 Ω input, or 75 Ω
input. To protect the attenuator and input mixer from damage, refer to
“Analyzer Input Protection” in Chapter 1 for maximum input level
requirements.
A3 Input Attenuator
The A3 input attenuator has a 0 to 60 dB range that provides input
attenuation in 10 dB steps. Pressing
PRESET or analyzer power-on
selects 10 dB attenuation. If POWERON LAST is selected, the analyzer is
reset to the settings in use when the analyzer was turned off.
A4 First Converter
The A4 first converter assembly converts incoming signals to a
2.1214 GHz first IF by mixing the 2.1214 GHz to 3.9214 GHz LO signal
from the A6 YTO assembly with the input signal. The first IF signal is
the summed signal from the mixing process. For analyzers that are not
equipped with a tracking generator, Option 010 or Option 011, the J4
output for the tracking generator is terminated.
FL1 Low-Pass Filter and AT1 Isolator
The first IF signal is routed through FL1, a 4.9 GHz low-pass filter, and
the AT1 isolator. The devices limit unwanted mixing products and
isolate the A4 first converter from the A5 second converter.
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