Agilent Technologies E8285A Manual page 31

AM, FM, or SSB Modulation Analysis
For AM, FM, or SSB signals, the 114.3 MHz signal is downconverted to
10.7 MHz and routed through a user-selected IF bandpass filter
(15 kHz or 230 kHz) that is centered around the 10.7 MHz IF. AM and
SSB signals are demodulated at this point; FM signals are
downconverted to a 700 kHz IF before demodulation. The demodulated
signal is routed to the Audio Analyzer 1 assembly for audio frequency
filtering. This assembly is also connected to the front-panel AUDIO IN
connector for direct audio measurements. Several low pass and high
pass filters can be selected, as well as a C-Message or optional CCITT
bandpass filter. Frequency and voltage measurements are then made
on this signal by the Measurement assembly. The signal is then routed
to the Audio Analyzer 2 assembly.
The Audio Analyzer 2 assembly routes the signal through a
user-selectable detector. A variable frequency notch filter may also be
selected for SINAD and distortion measurements. The detector's signal
is then sent to several other assemblies:
• The Measurement assembly measures and displays the modulation
• The Signaling Source Analyzer assembly for signaling decoding.
• The rear-panel AUD MONITOR OUTPUT connector for external use
• The front-panel VOLUME control and internal speaker to listen to
Figure 1-4 AM, FM, and SSB Signal Demodulation and Filtering
Receiver Assembly
114.3 MHz
IF 10.7 MHz
125 MHz
(centered around 10.7 MHz)
Audio Analyzer 2 Assembly
Selectable Detectors
RMS
RMS*SQRT2
Pk+
Pk-
.......
level (such as FM deviation) and provide the input to the
oscilloscope.
of the demodulated signal.
the demodulated signal.
15 kHz
230 kHz
IF Filters
10 MHz from
Reference Assembly
Variable Freq.
Notch Filter
RMS
Detector
Audio Analyzer 1 Assembly
AM Demod
SSB Demod
FM Demod
AUDIO IN
(front panel)
VOLUME
Signaling Source Analyzer
AUD MONITOR OUTPUT (Rear panel)
Measurement Assembly
Introduction
Product Description
Selectable Selectable
Low-Pass
High-Pass
Filters
Filters
DC Volts and
Audio Frequency
Measurements
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