Agilent Technologies 8590 Series Service Manual page 379

Assembly Descriptions and Block Diagrams
IF Section
Refer to the "A130 Narrow Bandwidth Assembly" section of Foldout
11-1. The narrow bandwidth assembly is inserted into one of the four
card-cage slots. The narrow bandwidth assembly receives the 21.4 MHz
AUX_IF from the A15 motherboard. The AUX_IF signal is available to
all the card-cage assemblies. The 21.4 MHz signal is downconverted to
a 8.56 kHz IF. This low IF frequency was chosen to facilitate the
necessary Q for the bandwidth filters and to eliminate the need for
bulky crystal circuits.
The 8.56 kHz IF is buffered, put through two poles of active filtering,
then the signal goes through 0 to 40 dB of step gain. After the step gain,
there are two more active filter poles before the signal is put through a
detector. If the analyzer is in log mode the signal is amplified
logarithmically. Otherwise, the signal is amplified with linear circuits.
The detected video signal is then routed back to the A15 motherboard
as VIDEO_IF. This signal then goes to the A16 processor video
assembly and converted to digital.
Refer to the "A14 Log Amplifier/Detector" section of the IF/Control
block diagram. Note that jumper W1 must be removed when Option 130
is installed in the analyzer. The video signal takes a different path
when Option 130 is installed and bandwidths greater than 300 Hz
(wide bandwidths) are selected. After the signal is detected on the A14
log amplifier assembly, the video is routed to A14J2, DAISY CHAIN
VIDEO OUTPUT, then W130 sends the video signal to the A130 narrow
bandwidth assembly at A130J3. This video signal goes to the output
multiplexer located on the A130 narrow bandwidth assembly. In the
wide bandwidths, this signal is selected and is then routed to back to
the A15 motherboard as VIDEO_IF.
The A130 narrow bandwidth assembly also has a DAISY CHAIN
VIDEO OUTPUT (A130 J2). However, this output is not currently in
use.
Chapter 9 379