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Model
8672A
Service
SERVICE SHEET
1
PRINCIPLES OF OPERATION
The HP Model
8672A
Synthesized
Signal Genera¬
tor
consists
of
the
A3 RF
Source Assembly,
A2
Controller Assembly
and the
Al
RF Output
Ass-
sembly. Figure 8-19
is
a
simplified block diagram.
The
Overall Troubleshooting
Block Diagram
shows
the interconnections between the major
assemblies.
Figure 8-20
shows
the physical location
of
these
assemblies in
the
Synthesizer.
The
Synthesizer's
RF output
signal
is
generated in
the
YTO Loop
of the
A3 RF
Source Assembly.
Through
the interconnection
of
the phase
lock
loops, the
output
signal
is
phase locked
to
the time
base.
The
power
supplies are also
part
of
the
A3
Assembly.
Digital
signals
from
the
A2 Controller Assembly
are
input to the
loop circuits to
control the
RF
output frequency.
The
frequency may be tuned
from the
front
panel or programmed through the
HP-IB Interface. The
RF
signal
from the YTO
is
passed
through
an
amplifier,
PIN modulator, YIG-
tuned-multiplier,
and stepped
attenuator
in
the
Al
RF Output
Assembly. An
ALC
loop controls the
level
and provides
amplitude modulation. The
attenuator's
output
is
connected to the
front
panel
RF Output
jack. The frequency
and
amplitude
modulation
modes are selected
by
circuits
within
the
Al
Assembly. The FM
is
added
to
the carrier in
the
A3
Assembly's
YTO Loop.
In
the local mode, the control
signals
are
input
from the front
panel. Programmed inputs come
through the HP-IB Interface to control frequency,
RF
level
functions,
and
modulation.
The front panel
annunciators indicate the
Synthe¬
sizer's
operating mode and
status.
Table 8-2
lists
the
status and
explains
the
functions monitored.
2-6.2
GHz
CONTROLLER
2-18.0
GHz
Figure 8-19.
Synthesizer's
Simplified
Block
Diagram
TOP VIEW
-Q.
+22V
ANNUNCIATOR'
POWER
SUPPLY
ANO
THERMALSHUTDOWN
ANNUNCIATORS
__
__
I
1-1
LJ
1
A3
"—J
RFSOURCE
PHASE LOCK LOOP
•STATUS
ANNUNCIATOR
RFOUTPUT
CONTROLLER
FRONT
Figure 8-20. Major Assembly
Locations
8-29
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