HP 8340b - 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