HP 8340B Manual page 466

The rear panel interface signals
(e.g.
HP-IB, SWEEP OUTPUT, Z-AXIS) are
also
routed through or
generated
in
the controller functional group.
The sweep control signal from the controller stops and
starts the sweep generator. As mentioned, during bandcrossings, the
sweep must
be stopped to
phase lock the YO before the sweep can continue. The controller monitors sweep events such as
bandcrossings, end of sweep,
and markers, and executes specific instructions according
to each
sweep
event.
FRONT PANEL
-
REAR PANEL
Front Panel
The front panel contains the user-interface displays and keyboard as well as various input and output
connectors. The displays have
a
dedicated microprocessor that keeps them updated. When the
instrument processor places display data into the display interface latch,
it signals the display
pro¬
cessor that information
is
ready. The display processor immediately takes the data from the
latch and
stores
it In
internal
memory. The data is handled when the display processor has time.
The
keyboard communicates directly with the instrument processor. When
a
key is pressed, the
instrument
processor either executes
that key (if
it is
a
single
key operation),
or
waits for completion of
the key sequence. Different key sequences
not only allow you to set the instrument for normal opera¬
tion, but also allow
access
to internal registers, latches,
D
to
A
converters, and calibration constants
for troubleshooting.
Rear Panel
A
rear panel schematic shows all interconnections between the rear panel connectors and related
internal assemblies.
RF SECTION
The RF
Section contains the microcircuits and control circuits that produce the
10 MHz
to
20.0 GHz
(HP
8341
B) or 26.5 GHz (HP 8340B) RF output from
the
2.3
to
7.0 GHz YO loop output.
The
RF output from the A45 directional coupler
in
the
YO
loop
is
fed to the modulator/splitter
(mod/
splitter)
in
the RF section. Band 0
(10
MHz
to
2.3
Ghz)
is
the heterodyne band and
is
produced by
mixing
a
swept
LO drive from the mod/splitter with the
phase-locked 3.7
GHz
oscillator output. The IF
signal from
the low band
mixer
is routed through the low band power amplifier, the switched-YIG-
tuned multiplier (SYTM), the high band coupler, and
the
90 dB step attenuator before it reaches the RF
output connector.
The SYTM
and high band coupler perform no function
in this band.
Band
1
(2.3 to
7.0 GHz)
is
the same as the YO fundamental frequency.
The RF
from the high band
output on the mod/splitter is
amplified by the high band
power
amplifier and passes through the
SYTM
to the high band coupler. Part of the RF
is
coupled to the high band detector for leveling through the
ALC Loop. After the coupler, the RF passes through the 90 dB step attenuator, to
the
RF
OUTPUT.
A-6
Assembly-Level Service Overall Instrument Theory
HP 8340B/41B